ISO/IEC 9899:201x Committee Draft April 12, 2011 N1570


FOREWORD. [Foreword]


1   ISO (the International Organization for Standardization) and IEC (the International
    Electrotechnical Commission) form the specialized system for worldwide
    standardization. National bodies that are member of ISO or IEC participate in the
    development of International Standards through technical committees established by the
    respective organization to deal with particular fields of technical activity. ISO and IEC
    technical committees collaborate in fields of mutual interest. Other international
    organizations, governmental and non-governmental, in liaison with ISO and IEC, also
    take part in the work.
2   International Standards are drafted in accordance with the rules given in the ISO/IEC
    Directives, Part 2. This International Standard was drafted in accordance with the fifth
    edition (2004).
3   In the field of information technology, ISO and IEC have established a joint technical
    committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
    committee are circulated to national bodies for voting. Publication as an International
    Standard requires approval by at least 75% of the national bodies casting a vote.
4   Attention is drawn to the possibility that some of the elements of this document may be
    the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
    or all such patent rights.
5   This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
    Information technology , Subcommittee SC 22, Programming languages, their
    environments and system software interfaces. The Working Group responsible for this
    standard (WG 14) maintains a site on the World Wide Web at http://www.open-
    std.org/JTC1/SC22/WG14/ containing additional information relevant to this
    standard such as a Rationale for many of the decisions made during its preparation and a
    log of Defect Reports and Responses.
6   This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
    corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
    ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
    -- conditional (optional) features (including some that were previously mandatory)
    -- support for multiple threads of execution including an improved memory sequencing
       model, atomic objects, and thread-local storage (<stdatomic.h> and
       <threads.h>)
    -- additional floating-point characteristic macros (<float.h>)
    -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
    -- Unicode characters and          strings   (<uchar.h>)       (originally   specified    in
       ISO/IEC TR 19769:2004)
    -- type-generic expressions
    -- static assertions
    -- anonymous structures and unions
    -- no-return functions
    -- macros to create complex numbers (<complex.h>)
    -- support for opening files for exclusive access
    -- removed the gets function (<stdio.h>)
    -- added the aligned_alloc, at_quick_exit, and quick_exit functions
       (<stdlib.h>)
    -- (conditional) support for bounds-checking interfaces (originally specified in
       ISO/IEC TR 24731-1:2007)
    -- (conditional) support for analyzability
7   Major changes in the second edition included:
    -- restricted character set support via digraphs and <iso646.h> (originally specified
       in AMD1)
    -- wide character library support in <wchar.h> and <wctype.h> (originally
       specified in AMD1)
    -- more precise aliasing rules via effective type
    -- restricted pointers
    -- variable length arrays
    -- flexible array members
    -- static and type qualifiers in parameter array declarators
    -- complex (and imaginary) support in <complex.h>
    -- type-generic math macros in <tgmath.h>
    -- the long long int type and library functions
    -- increased minimum translation limits
    -- additional floating-point characteristics in <float.h>
    -- remove implicit int
    -- reliable integer division
    -- universal character names (\u and \U)
    -- extended identifiers
    -- hexadecimal floating-point constants and %a and %A printf/scanf conversion
       specifiers
    -- compound literals
    -- designated initializers
    -- // comments
    -- extended integer types and library functions in <inttypes.h> and <stdint.h>
    -- remove implicit function declaration
    -- preprocessor arithmetic done in intmax_t/uintmax_t
    -- mixed declarations and code
    -- new block scopes for selection and iteration statements
    -- integer constant type rules
    -- integer promotion rules
    -- macros with a variable number of arguments
    -- the vscanf family of functions in <stdio.h> and <wchar.h>
    -- additional math library functions in <math.h>
    -- treatment of error conditions by math library functions (math_errhandling)
    -- floating-point environment access in <fenv.h>
    -- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
    -- trailing comma allowed in enum declaration
    -- %lf conversion specifier allowed in printf
    -- inline functions
    -- the snprintf family of functions in <stdio.h>
    -- boolean type in <stdbool.h>
    -- idempotent type qualifiers
    -- empty macro arguments
    -- new structure type compatibility rules (tag compatibility)
    -- additional predefined macro names
    -- _Pragma preprocessing operator
    -- standard pragmas
    -- _ _func_ _ predefined identifier
    -- va_copy macro
    -- additional strftime conversion specifiers
    -- LIA compatibility annex
    -- deprecate ungetc at the beginning of a binary file
    -- remove deprecation of aliased array parameters
    -- conversion of array to pointer not limited to lvalues
    -- relaxed constraints on aggregate and union initialization
    -- relaxed restrictions on portable header names
    -- return without expression not permitted in function that returns a value (and vice
       versa)
8   Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H,
    I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
    the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
    are also for information only.

INTRODUCTION. [Introduction]


1   With the introduction of new devices and extended character sets, new features may be
    added to this International Standard. Subclauses in the language and library clauses warn
    implementors and programmers of usages which, though valid in themselves, may
    conflict with future additions.
2   Certain features are obsolescent , which means that they may be considered for
    withdrawal in future revisions of this International Standard. They are retained because
    of their widespread use, but their use in new implementations (for implementation
    features) or new programs (for language [6.11] or library features [7.31]) is discouraged.
3   This International Standard is divided into four major subdivisions:
    -- preliminary elements (clauses 1-4);
    -- the characteristics of environments that translate and execute C programs (clause 5);
    -- the language syntax, constraints, and semantics (clause 6);
    -- the library facilities (clause 7).
4   Examples are provided to illustrate possible forms of the constructions described.
    Footnotes are provided to emphasize consequences of the rules described in that
    subclause or elsewhere in this International Standard. References are used to refer to
    other related subclauses. Recommendations are provided to give advice or guidance to
    implementors. Annexes provide additional information and summarize the information
    contained in this International Standard. A bibliography lists documents that were
    referred to during the preparation of the standard.
5   The language clause (clause 6) is derived from ``The C Reference Manual''.
6   The library clause (clause 7) is based on the 1984 /usr/group Standard .
xviii                         Introduction
    INTERNATIONAL STANDARD                                ©ISO/IEC                 ISO/IEC 9899:201x
    Programming languages -- C


1. [Scope]


1   This International Standard specifies the form and establishes the interpretation of
    programs written in the C programming language.1) It specifies
    -- the representation of C programs;
    -- the syntax and constraints of the C language;
    -- the semantic rules for interpreting C programs;
    -- the representation of input data to be processed by C programs;
    -- the representation of output data produced by C programs;
    -- the restrictions and limits imposed by a conforming implementation of C.
Footnote 1) This International Standard is designed to promote the portability of C programs among a variety of
         data-processing systems. It is intended for use by implementors and programmers.
2   This International Standard does not specify
    -- the mechanism by which C programs are transformed for use by a data-processing
       system;
    -- the mechanism by which C programs are invoked for use by a data-processing
       system;
    -- the mechanism by which input data are transformed for use by a C program;
    -- the mechanism by which output data are transformed after being produced by a C
       program;
    -- the size or complexity of a program and its data that will exceed the capacity of any
       specific data-processing system or the capacity of a particular processor;
    -- all minimal requirements of a data-processing system that is capable of supporting a
       conforming implementation.

2. [Normative references]


1   The following referenced documents are indispensable for the application of this
    document. For dated references, only the edition cited applies. For undated references,
    the latest edition of the referenced document (including any amendments) applies.
2   ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for
    use in the physical sciences and technology .
3   ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information
    interchange.
4   ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental
    terms.
5   ISO 4217, Codes for the representation of currencies and funds.
6   ISO 8601, Data elements and interchange formats -- Information interchange --
    Representation of dates and times.
7   ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded
    Character Set (UCS).
8   IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
    designated IEC 559:1989).


3. [Terms, definitions, and symbols]


1   For the purposes of this International Standard, the following definitions apply. Other
    terms are defined where they appear in italic type or on the left side of a syntax rule.
    Terms explicitly defined in this International Standard are not to be presumed to refer
    implicitly to similar terms defined elsewhere. Terms not defined in this International
    Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not
    defined in this International Standard are to be interpreted according to ISO 31-11.

3.1 [Terms, definitions, and symbols]


1   access
    execution-time action to read or modify the value of an object
2   NOTE 1   Where only one of these two actions is meant, ``read'' or ``modify'' is used.

3   NOTE 2   ``Modify'' includes the case where the new value being stored is the same as the previous value.

4   NOTE 3   Expressions that are not evaluated do not access objects.


3.2 [Terms, definitions, and symbols]


1   alignment
    requirement that objects of a particular type be located on storage boundaries with
    addresses that are particular multiples of a byte address

3.3 [Terms, definitions, and symbols]


1   argument
    actual argument
    actual parameter (deprecated)
    expression in the comma-separated list bounded by the parentheses in a function call
    expression, or a sequence of preprocessing tokens in the comma-separated list bounded
    by the parentheses in a function-like macro invocation

3.4 [Terms, definitions, and symbols]


1   behavior
    external appearance or action

3.4.1 [Terms, definitions, and symbols]


1   implementation-defined behavior
    unspecified behavior where each implementation documents how the choice is made
2   EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
    when a signed integer is shifted right.


3.4.2 [Terms, definitions, and symbols]


1   locale-specific behavior
    behavior that depends on local conventions of nationality, culture, and language that each
    implementation documents
2   EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
    characters other than the 26 lowercase Latin letters.


3.4.3 [Terms, definitions, and symbols]


1   undefined behavior
    behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
    for which this International Standard imposes no requirements
2   NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
    results, to behaving during translation or program execution in a documented manner characteristic of the
    environment (with or without the issuance of a diagnostic message), to terminating a translation or
    execution (with the issuance of a diagnostic message).

3   EXAMPLE        An example of undefined behavior is the behavior on integer overflow.


3.4.4 [Terms, definitions, and symbols]


1   unspecified behavior
    use of an unspecified value, or other behavior where this International Standard provides
    two or more possibilities and imposes no further requirements on which is chosen in any
    instance
2   EXAMPLE        An example of unspecified behavior is the order in which the arguments to a function are
    evaluated.


3.5 [Terms, definitions, and symbols]


1   bit
    unit of data storage in the execution environment large enough to hold an object that may
    have one of two values
2   NOTE      It need not be possible to express the address of each individual bit of an object.


3.6 [Terms, definitions, and symbols]


1   byte
    addressable unit of data storage large enough to hold any member of the basic character
    set of the execution environment
2   NOTE 1     It is possible to express the address of each individual byte of an object uniquely.

3   NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
    defined. The least significant bit is called the low-order bit ; the most significant bit is called the high-order
    bit .


3.7 [Terms, definitions, and symbols]


1   character
    abstract member of a set of elements used for the organization, control, or
    representation of data

3.7.1 [Terms, definitions, and symbols]


1   character
    single-byte character
    C bit representation that fits in a byte

3.7.2 [Terms, definitions, and symbols]


1   multibyte character
    sequence of one or more bytes representing a member of the extended character set of
    either the source or the execution environment
2   NOTE    The extended character set is a superset of the basic character set.


3.7.3 [Terms, definitions, and symbols]


1   wide character
    value representable by an object of type wchar_t, capable of representing any character
    in the current locale

3.8 [Terms, definitions, and symbols]


1   constraint
    restriction, either syntactic or semantic, by which the exposition of language elements is
    to be interpreted

3.9 [Terms, definitions, and symbols]


1   correctly rounded result
    representation in the result format that is nearest in value, subject to the current rounding
    mode, to what the result would be given unlimited range and precision

3.10 [Terms, definitions, and symbols]


1   diagnostic message
    message belonging to an implementation-defined subset of the implementation's message
    output

3.11 [Terms, definitions, and symbols]


1   forward reference
    reference to a later subclause of this International Standard that contains additional
    information relevant to this subclause

3.12 [Terms, definitions, and symbols]


1   implementation
    particular set of software, running in a particular translation environment under particular
    control options, that performs translation of programs for, and supports execution of
    functions in, a particular execution environment

3.13 [Terms, definitions, and symbols]


1   implementation limit
    restriction imposed upon programs by the implementation

3.14 [Terms, definitions, and symbols]


1   memory location
    either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
    nonzero width

2   NOTE 1 Two threads of execution can update and access separate memory locations without interfering
    with each other.

3   NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
    applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
    two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
    declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
    members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
    intervening bit-fields happen to be.

4   EXAMPLE        A structure declared as
             struct {
                   char a;
                   int b:5, c:11, :0, d:8;
                   struct { int ee:8; } e;
             }
    contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
    memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
    and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
    modified, but b and a, for example, can be.


3.15 [Terms, definitions, and symbols]


1   object
    region of data storage in the execution environment, the contents of which can represent
    values
2   NOTE      When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.


3.16 [Terms, definitions, and symbols]


1   parameter
    formal parameter
    formal argument (deprecated)
    object declared as part of a function declaration or definition that acquires a value on
    entry to the function, or an identifier from the comma-separated list bounded by the
    parentheses immediately following the macro name in a function-like macro definition

3.17 [Terms, definitions, and symbols]


1   recommended practice
    specification that is strongly recommended as being in keeping with the intent of the
    standard, but that may be impractical for some implementations

3.18 [Terms, definitions, and symbols]


1   runtime-constraint
    requirement on a program when calling a library function
2   NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
    need not be diagnosed at translation time.

3   NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
    constraints for a library function are not violated by the program; see K.3.1.4.


3.19 [Terms, definitions, and symbols]


1   value
    precise meaning of the contents of an object when interpreted as having a specific type

3.19.1 [Terms, definitions, and symbols]


1   implementation-defined value
    unspecified value where each implementation documents how the choice is made

3.19.2 [Terms, definitions, and symbols]


1   indeterminate value
    either an unspecified value or a trap representation

3.19.3 [Terms, definitions, and symbols]


1   unspecified value
    valid value of the relevant type where this International Standard imposes no
    requirements on which value is chosen in any instance
2   NOTE     An unspecified value cannot be a trap representation.


3.19.4 [Terms, definitions, and symbols]


1   trap representation
    an object representation that need not represent a value of the object type

3.19.5 [Terms, definitions, and symbols]


1   perform a trap
    interrupt execution of the program such that no further operations are performed
2   NOTE In this International Standard, when the word ``trap'' is not immediately followed by
    ``representation'', this is the intended usage.2)

Footnote 2) For example, ``Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap
         representation might perform a trap but is not required to (see 6.2.6.1).

3.20 [Terms, definitions, and symbols]


1    x
    ceiling of x : the least integer greater than or equal to x
2   EXAMPLE       2. 4 is 3, -2. 4 is -2.


3.21 [Terms, definitions, and symbols]


1    x
    floor of x : the greatest integer less than or equal to x
2   EXAMPLE       2. 4 is 2, -2. 4 is -3.

4. [Conformance]


1   In this International Standard, ``shall'' is to be interpreted as a requirement on an
    implementation or on a program; conversely, ``shall not'' is to be interpreted as a
    prohibition.
2   If a ``shall'' or ``shall not'' requirement that appears outside of a constraint or runtime-
    constraint is violated, the behavior is undefined. Undefined behavior is otherwise
    indicated in this International Standard by the words ``undefined behavior'' or by the
    omission of any explicit definition of behavior. There is no difference in emphasis among
    these three; they all describe ``behavior that is undefined''.
3   A program that is correct in all other aspects, operating on correct data, containing
    unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
4   The implementation shall not successfully translate a preprocessing translation unit
    containing a #error preprocessing directive unless it is part of a group skipped by
    conditional inclusion.
5   A strictly conforming program shall use only those features of the language and library
    specified in this International Standard.3) It shall not produce output dependent on any
    unspecified, undefined, or implementation-defined behavior, and shall not exceed any
    minimum implementation limit.
Footnote 3) A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
         by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
                 #ifdef _ _STDC_IEC_559_ _ /* FE_UPWARD defined */
                    /* ... */
                    fesetround(FE_UPWARD);
                    /* ... */
                 #endif
6   The two forms of conforming implementation are hosted and freestanding. A conforming
    hosted implementation shall accept any strictly conforming program. A conforming
    freestanding implementation shall accept any strictly conforming program in which the 
    use of the features specified in the library clause (clause 7) is confined to the contents of
    the standard headers <float.h>, <iso646.h>, <limits.h>, <stdalign.h>,
    <stdarg.h>,           <stdbool.h>,            <stddef.h>,           <stdint.h>,          and
    <stdnoreturn.h>. A conforming implementation may have extensions (including
    additional library functions), provided they do not alter the behavior of any strictly
    conforming program.4)

Footnote 4) This implies that a conforming implementation reserves no identifiers other than those explicitly
         reserved in this International Standard.
7   A conforming program is one that is acceptable to a conforming implementation.5)
Footnote 5) Strictly conforming programs are intended to be maximally portable among conforming
         implementations. Conforming programs may depend upon nonportable features of a conforming
         implementation.
8   An implementation shall be accompanied by a document that defines all implementation-
    defined and locale-specific characteristics and all extensions.
    Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
    characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
    (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15),
    variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h>
    (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20),
    <stdnoreturn.h> (7.23).

5. [Environment]


1   An implementation translates C source files and executes C programs in two data-
    processing-system environments, which will be called the translation environment and
    the execution environment in this International Standard. Their characteristics define and
    constrain the results of executing conforming C programs constructed according to the
    syntactic and semantic rules for conforming implementations.
    Forward references: In this clause, only a few of many possible forward references
    have been noted.

5.1 [Conceptual models]

 Conceptual models

5.1.1 [Translation environment]

 Translation environment

5.1.1.1 [Program structure]


1   A C program need not all be translated at the same time. The text of the program is kept
    in units called source files, (or preprocessing files) in this International Standard. A
    source file together with all the headers and source files included via the preprocessing
    directive #include is known as a preprocessing translation unit . After preprocessing, a
    preprocessing translation unit is called a translation unit . Previously translated translation
    units may be preserved individually or in libraries. The separate translation units of a
    program communicate by (for example) calls to functions whose identifiers have external
    linkage, manipulation of objects whose identifiers have external linkage, or manipulation
    of data files. Translation units may be separately translated and then later linked to
    produce an executable program.
    Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
    preprocessing directives (6.10).

5.1.1.2 [Translation phases]


1   The precedence among the syntax rules of translation is specified by the following
    phases.6)
         1.   Physical source file multibyte characters are mapped, in an implementation-
              defined manner, to the source character set (introducing new-line characters for
              end-of-line indicators) if necessary. Trigraph sequences are replaced by
              corresponding single-character internal representations.

     2.   Each instance of a backslash character (\) immediately followed by a new-line
          character is deleted, splicing physical source lines to form logical source lines.
          Only the last backslash on any physical source line shall be eligible for being part
          of such a splice. A source file that is not empty shall end in a new-line character,
          which shall not be immediately preceded by a backslash character before any such
          splicing takes place.
     3.   The source file is decomposed into preprocessing tokens7) and sequences of
          white-space characters (including comments). A source file shall not end in a
          partial preprocessing token or in a partial comment. Each comment is replaced by
          one space character. New-line characters are retained. Whether each nonempty
          sequence of white-space characters other than new-line is retained or replaced by
          one space character is implementation-defined.
     4. Preprocessing directives are executed, macro invocations are expanded, and
        _Pragma unary operator expressions are executed. If a character sequence that
        matches the syntax of a universal character name is produced by token
        concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
        directive causes the named header or source file to be processed from phase 1
        through phase 4, recursively. All preprocessing directives are then deleted.
     5. Each source character set member and escape sequence in character constants and
        string literals is converted to the corresponding member of the execution character
        set; if there is no corresponding member, it is converted to an implementation-
        defined member other than the null (wide) character.8)
     6.   Adjacent string literal tokens are concatenated.
     7. White-space characters separating tokens are no longer significant. Each
        preprocessing token is converted into a token. The resulting tokens are
        syntactically and semantically analyzed and translated as a translation unit.
     8.   All external object and function references are resolved. Library components are
          linked to satisfy external references to functions and objects not defined in the
          current translation. All such translator output is collected into a program image
          which contains information needed for execution in its execution environment.
    Forward references: universal character names (6.4.3), lexical elements (6.4),
    preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).

Footnote 6) Implementations shall behave as if these separate phases occur, even though many are typically folded
          together in practice. Source files, translation units, and translated translation units need not
          necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
          and any external representation. The description is conceptual only, and does not specify any
          particular implementation.
Footnote 7) As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is
          context-dependent. For example, see the handling of < within a #include preprocessing directive.
Footnote 8) An implementation need not convert all non-corresponding source characters to the same execution
          character.

5.1.1.3 [Diagnostics]


1   A conforming implementation shall produce at least one diagnostic message (identified in
    an implementation-defined manner) if a preprocessing translation unit or translation unit
    contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
    specified as undefined or implementation-defined. Diagnostic messages need not be
    produced in other circumstances.9)
Footnote 9) The intent is that an implementation should identify the nature of, and where possible localize, each
         violation. Of course, an implementation is free to produce any number of diagnostics as long as a
         valid program is still correctly translated. It may also successfully translate an invalid program.
2   EXAMPLE        An implementation shall issue a diagnostic for the translation unit:
             char i;
             int i;
    because in those cases where wording in this International Standard describes the behavior for a construct
    as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.


5.1.2 [Execution environments]


1   Two execution environments are defined: freestanding and hosted . In both cases,
    program startup occurs when a designated C function is called by the execution
    environment. All objects with static storage duration shall be initialized (set to their
    initial values) before program startup. The manner and timing of such initialization are
    otherwise unspecified. Program termination returns control to the execution
    environment.
    Forward references: storage durations of objects (6.2.4), initialization (6.7.9).

5.1.2.1 [Freestanding environment]


1   In a freestanding environment (in which C program execution may take place without any
    benefit of an operating system), the name and type of the function called at program
    startup are implementation-defined. Any library facilities available to a freestanding
    program, other than the minimal set required by clause 4, are implementation-defined.
2   The effect of program termination in a freestanding environment is implementation-
    defined.

5.1.2.2 [Hosted environment]


1   A hosted environment need not be provided, but shall conform to the following
    specifications if present.


5.1.2.2.1 [Program startup]


1   The function called at program startup is named main. The implementation declares no
    prototype for this function. It shall be defined with a return type of int and with no
    parameters:
            int main(void) { /* ... */ }
    or with two parameters (referred to here as argc and argv, though any names may be
    used, as they are local to the function in which they are declared):
            int main(int argc, char *argv[]) { /* ... */ }
    or equivalent;10) or in some other implementation-defined manner.
Footnote 10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
        char ** argv, and so on.
2   If they are declared, the parameters to the main function shall obey the following
    constraints:
    -- The value of argc shall be nonnegative.
    -- argv[argc] shall be a null pointer.
    -- If the value of argc is greater than zero, the array members argv[0] through
       argv[argc-1] inclusive shall contain pointers to strings, which are given
       implementation-defined values by the host environment prior to program startup. The
       intent is to supply to the program information determined prior to program startup
       from elsewhere in the hosted environment. If the host environment is not capable of
       supplying strings with letters in both uppercase and lowercase, the implementation
       shall ensure that the strings are received in lowercase.
    -- If the value of argc is greater than zero, the string pointed to by argv[0]
       represents the program name; argv[0][0] shall be the null character if the
       program name is not available from the host environment. If the value of argc is
       greater than one, the strings pointed to by argv[1] through argv[argc-1]
       represent the program parameters.
    -- The parameters argc and argv and the strings pointed to by the argv array shall
       be modifiable by the program, and retain their last-stored values between program
       startup and program termination.

5.1.2.2.2 [Program execution]


1   In a hosted environment, a program may use all the functions, macros, type definitions,
    and objects described in the library clause (clause 7).


5.1.2.2.3 [Program termination]


1   If the return type of the main function is a type compatible with int, a return from the
    initial call to the main function is equivalent to calling the exit function with the value
    returned by the main function as its argument;11) reaching the } that terminates the
    main function returns a value of 0. If the return type is not compatible with int, the
    termination status returned to the host environment is unspecified.
    Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).
Footnote 11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
        will have ended in the former case, even where they would not have in the latter.

5.1.2.3 [Program execution]


1   The semantic descriptions in this International Standard describe the behavior of an
    abstract machine in which issues of optimization are irrelevant.
2   Accessing a volatile object, modifying an object, modifying a file, or calling a function
    that does any of those operations are all side effects,12) which are changes in the state of
    the execution environment. Evaluation of an expression in general includes both value
    computations and initiation of side effects. Value computation for an lvalue expression
    includes determining the identity of the designated object.
Footnote 12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
        flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
        values of floating-point operations. Implementations that support such floating-point state are
        required to regard changes to it as side effects -- see annex F for details. The floating-point
        environment library <fenv.h> provides a programming facility for indicating when these side
        effects matter, freeing the implementations in other cases.
3   Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
    executed by a single thread, which induces a partial order among those evaluations.
    Given any two evaluations A and B, if A is sequenced before B, then the execution of A
    shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
    sequenced after A.) If A is not sequenced before or after B, then A and B are
    unsequenced . Evaluations A and B are indeterminately sequenced when A is sequenced
    either before or after B, but it is unspecified which.13) The presence of a sequence point
    between the evaluation of expressions A and B implies that every value computation and
    side effect associated with A is sequenced before every value computation and side effect
    associated with B. (A summary of the sequence points is given in annex C.)
Footnote 13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations
        cannot interleave, but can be executed in any order.
4   In the abstract machine, all expressions are evaluated as specified by the semantics. An
    actual implementation need not evaluate part of an expression if it can deduce that its
    value is not used and that no needed side effects are produced (including any caused by

     calling a function or accessing a volatile object).
5    When the processing of the abstract machine is interrupted by receipt of a signal, the
     values of objects that are neither lock-free atomic objects nor of type volatile
     sig_atomic_t are unspecified, as is the state of the floating-point environment. The
     value of any object modified by the handler that is neither a lock-free atomic object nor of
     type volatile sig_atomic_t becomes indeterminate when the handler exits, as
     does the state of the floating-point environment if it is modified by the handler and not
     restored to its original state.
6    The least requirements on a conforming implementation are:
     -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract
        machine.
     -- At program termination, all data written into files shall be identical to the result that
        execution of the program according to the abstract semantics would have produced.
     -- The input and output dynamics of interactive devices shall take place as specified in
        7.21.3. The intent of these requirements is that unbuffered or line-buffered output
        appear as soon as possible, to ensure that prompting messages actually appear prior to
        a program waiting for input.
     This is the observable behavior of the program.
7    What constitutes an interactive device is implementation-defined.
8    More stringent correspondences between abstract and actual semantics may be defined by
     each implementation.
9    EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
     semantics: at every sequence point, the values of the actual objects would agree with those specified by the
     abstract semantics. The keyword volatile would then be redundant.
10   Alternatively, an implementation might perform various optimizations within each translation unit, such
     that the actual semantics would agree with the abstract semantics only when making function calls across
     translation unit boundaries. In such an implementation, at the time of each function entry and function
     return where the calling function and the called function are in different translation units, the values of all
     externally linked objects and of all objects accessible via pointers therein would agree with the abstract
     semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
     function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
     type of implementation, objects referred to by interrupt service routines activated by the signal function
     would require explicit specification of volatile storage, as well as other implementation-defined
     restrictions.

11   EXAMPLE 2       In executing the fragment
              char c1, c2;
              /* ... */
              c1 = c1 + c2;
     the ``integer promotions'' require that the abstract machine promote the value of each variable to int size
     and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
     overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
     produce the same result, possibly omitting the promotions.

12   EXAMPLE 3       Similarly, in the fragment
              float f1, f2;
              double d;
              /* ... */
              f1 = f2 * d;
     the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
     that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
     were replaced by the constant 2.0, which has type double).

13   EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
     semantics. Values are independent of whether they are represented in a register or in memory. For
     example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
     is required to round to the precision of the storage type. In particular, casts and assignments are required to
     perform their specified conversion. For the fragment
              double d1, d2;
              float f;
              d1 = f = expression;
              d2 = (float) expression;
     the values assigned to d1 and d2 are required to have been converted to float.

14   EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
     precision as well as range. The implementation cannot generally apply the mathematical associative rules
     for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
     overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
     rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
     numbers are often not valid (see F.9).
              double x, y, z;
              /* ... */
              x = (x * y) * z;            //   not equivalent to x   *= y * z;
              z = (x - y) + y ;           //   not equivalent to z   = x;
              z = x + x * y;              //   not equivalent to z   = x * (1.0 + y);
              y = x / 5.0;                //   not equivalent to y   = x * 0.2;

15   EXAMPLE 6       To illustrate the grouping behavior of expressions, in the following fragment
              int a, b;
              /* ... */
              a = a + 32760 + b + 5;
     the expression statement behaves exactly the same as
              a = (((a + 32760) + b) + 5);
     due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
     next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
     which overflows produce an explicit trap and in which the range of values representable by an int is
     [-32768, +32767], the implementation cannot rewrite this expression as
              a = ((a + b) + 32765);
     since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap

     while the original expression would not; nor can the expression be rewritten either as
              a = ((a + 32765) + b);
     or
              a = (a + (b + 32765));
     since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine
     in which overflow silently generates some value and where positive and negative overflows cancel, the
     above expression statement can be rewritten by the implementation in any of the above ways because the
     same result will occur.

16   EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the
     following fragment
              #include <stdio.h>
              int sum;
              char *p;
              /* ... */
              sum = sum * 10 - '0' + (*p++ = getchar());
     the expression statement is grouped as if it were written as
              sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
     but the actual increment of p can occur at any time between the previous sequence point and the next
     sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
     value.

     Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), floating-
     point environment <fenv.h> (7.6), the signal function (7.14), files (7.21.3).

5.1.2.4 [Multi-threaded executions and data races]


1    Under a hosted implementation, a program can have more than one thread of execution
     (or thread ) running concurrently. The execution of each thread proceeds as defined by
     the remainder of this standard. The execution of the entire program consists of an
     execution of all of its threads.14) Under a freestanding implementation, it is
     implementation-defined whether a program can have more than one thread of execution.
Footnote 14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
         atomic operations, for example, allow executions inconsistent with a simple interleaving as described
         below.
2    The value of an object visible to a thread T at a particular point is the initial value of the
     object, a value stored in the object by T , or a value stored in the object by another thread,
     according to the rules below.
3    NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
     the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
     implicitly supports a simpler view for more restricted programs.

4    Two expression evaluations conflict if one of them modifies a memory location and the
     other one reads or modifies the same memory location.

5    The library defines a number of atomic operations (7.17) and operations on mutexes
     (7.26.4) that are specially identified as synchronization operations. These operations play
     a special role in making assignments in one thread visible to another. A synchronization
     operation on one or more memory locations is either an acquire operation, a release
     operation, both an acquire and release operation, or a consume operation. A
     synchronization operation without an associated memory location is a fence and can be
     either an acquire fence, a release fence, or both an acquire and release fence. In addition,
     there are relaxed atomic operations, which are not synchronization operations, and
     atomic read-modify-write operations, which have special characteristics.
6    NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
     composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
     operation on those same locations. Informally, performing a release operation on A forces prior side effects
     on other memory locations to become visible to other threads that later perform an acquire or consume
     operation on A. We do not include relaxed atomic operations as synchronization operations although, like
     synchronization operations, they cannot contribute to data races.

7    All modifications to a particular atomic object M occur in some particular total order,
     called the modification order of M . If A and B are modifications of an atomic object M ,
     and A happens before B, then A shall precede B in the modification order of M , which is
     defined below.
8    NOTE 3     This states that the modification orders must respect the ``happens before'' relation.

9    NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
     combined into a single total order for all objects. In general this will be impossible since different threads
     may observe modifications to different variables in inconsistent orders.

10   A release sequence headed by a release operation A on an atomic object M is a maximal
     contiguous sub-sequence of side effects in the modification order of M , where the first
     operation is A and every subsequent operation either is performed by the same thread that
     performed the release or is an atomic read-modify-write operation.
11   Certain library calls synchronize with other library calls performed by another thread. In
     particular, an atomic operation A that performs a release operation on an object M
     synchronizes with an atomic operation B that performs an acquire operation on M and
     reads a value written by any side effect in the release sequence headed by A.
12   NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
     described below. Such a requirement would sometimes interfere with efficient implementation.

13   NOTE 6 The specifications of the synchronization operations define when one reads the value written by
     another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
     order. Each mutex acquisition ``reads the value written'' by the last mutex release.

14   An evaluation A carries a dependency 15) to an evaluation B if:

     -- the value of A is used as an operand of B, unless:
           ·   B is an invocation of the kill_dependency macro,
           ·   A is the left operand of a && or || operator,
           ·   A is the left operand of a ? : operator, or
           ·   A is the left operand of a , operator;
         or
     -- A writes a scalar object or bit-field M , B reads from M the value written by A, and A
        is sequenced before B, or
     -- for some evaluation X , A carries a dependency to X and X carries a dependency to B.
Footnote 15) The ``carries a dependency'' relation is a subset of the ``sequenced before'' relation, and is similarly
         strictly intra-thread.
15   An evaluation A is dependency-ordered before16) an evaluation B if:
     -- A performs a release operation on an atomic object M , and, in another thread, B
        performs a consume operation on M and reads a value written by any side effect in
        the release sequence headed by A, or
     -- for some evaluation X , A is dependency-ordered before X and X carries a
        dependency to B.
Footnote 16) The ``dependency-ordered before'' relation is analogous to the ``synchronizes with'' relation, but uses
         release/consume in place of release/acquire.
16   An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
     is dependency-ordered before B, or, for some evaluation X :
     -- A synchronizes with X and X is sequenced before B,
     -- A is sequenced before X and X inter-thread happens before B, or
     -- A inter-thread happens before X and X inter-thread happens before B.
17   NOTE 7 The ``inter-thread happens before'' relation describes arbitrary concatenations of ``sequenced
     before'', ``synchronizes with'', and ``dependency-ordered before'' relationships, with two exceptions. The
     first exception is that a concatenation is not permitted to end with ``dependency-ordered before'' followed
     by ``sequenced before''. The reason for this limitation is that a consume operation participating in a
     ``dependency-ordered before'' relationship provides ordering only with respect to operations to which this
     consume operation actually carries a dependency. The reason that this limitation applies only to the end of
     such a concatenation is that any subsequent release operation will provide the required ordering for a prior
     consume operation. The second exception is that a concatenation is not permitted to consist entirely of
     ``sequenced before''. The reasons for this limitation are (1) to permit ``inter-thread happens before'' to be
     transitively closed and (2) the ``happens before'' relation, defined below, provides for relationships
     consisting entirely of ``sequenced before''.

18   An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
     thread happens before B.

19   A visible side effect A on an object M with respect to a value computation B of M
     satisfies the conditions:
     -- A happens before B, and
     -- there is no other side effect X to M such that A happens before X and X happens
         before B.
     The value of a non-atomic scalar object M , as determined by evaluation B, shall be the
     value stored by the visible side effect A.
20   NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
     race and the behavior is undefined.

21   NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
     detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
     restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
     execution.

22   The visible sequence of side effects on an atomic object M , with respect to a value
     computation B of M , is a maximal contiguous sub-sequence of side effects in the
     modification order of M , where the first side effect is visible with respect to B, and for
     every subsequent side effect, it is not the case that B happens before it. The value of an
     atomic object M , as determined by evaluation B, shall be the value stored by some
     operation in the visible sequence of M with respect to B. Furthermore, if a value
     computation A of an atomic object M happens before a value computation B of M , and
     the value computed by A corresponds to the value stored by side effect X , then the value
     computed by B shall either equal the value computed by A, or be the value stored by side
     effect Y , where Y follows X in the modification order of M .
23   NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
     both operations are ``relaxed'' loads. By doing so, we effectively make the ``cache coherence'' guarantee
     provided by most hardware available to C atomic operations.

24   NOTE 11 The visible sequence depends on the ``happens before'' relation, which in turn depends on the
     values observed by loads of atomics, which we are restricting here. The intended reading is that there must
     exist an association of atomic loads with modifications they observe that, together with suitably chosen
     modification orders and the ``happens before'' relation derived as described above, satisfy the resulting
     constraints as imposed here.

25   The execution of a program contains a data race if it contains two conflicting actions in
     different threads, at least one of which is not atomic, and neither happens before the
     other. Any such data race results in undefined behavior.
26   NOTE 12 It can be shown that programs that correctly use simple mutexes and
     memory_order_seq_cst operations to prevent all data races, and use no other synchronization
     operations, behave as though the operations executed by their constituent threads were simply interleaved,
     with each value computation of an object being the last value stored in that interleaving. This is normally
     referred to as ``sequential consistency''. However, this applies only to data-race-free programs, and data-
     race-free programs cannot observe most program transformations that do not change single-threaded
     program semantics. In fact, most single-threaded program transformations continue to be allowed, since
     any program that behaves differently as a result must contain undefined behavior.

27   NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
     that would not be modified by the abstract machine are generally precluded by this standard, since such an
     assignment might overwrite another assignment by a different thread in cases in which an abstract machine
     execution would not have encountered a data race. This includes implementations of data member
     assignment that overwrite adjacent members in separate memory locations. We also generally preclude
     reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
     "visible sequence" rules.

28   NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
     not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
     race. However, they are typically valid in the context of an optimizing compiler that targets a specific
     machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
     is not tolerant of races or provides hardware race detection.

5.2 [Environmental considerations]

 Environmental considerations

5.2.1 [Character sets]


1   Two sets of characters and their associated collating sequences shall be defined: the set in
    which source files are written (the source character set ), and the set interpreted in the
    execution environment (the execution character set ). Each set is further divided into a
    basic character set , whose contents are given by this subclause, and a set of zero or more
    locale-specific members (which are not members of the basic character set) called
    extended characters. The combined set is also called the extended character set . The
    values of the members of the execution character set are implementation-defined.
2   In a character constant or string literal, members of the execution character set shall be
    represented by corresponding members of the source character set or by escape
    sequences consisting of the backslash \ followed by one or more characters. A byte with
    all bits set to 0, called the null character , shall exist in the basic execution character set; it
    is used to terminate a character string.
3   Both the basic source and basic execution character sets shall have the following
    members: the 26 uppercase letters of the Latin alphabet
            A    B    C     D   E     F   G   H    I    J    K    L    M
            N    O    P     Q   R     S   T   U    V    W    X    Y    Z
    the 26 lowercase letters of the Latin alphabet
            a    b    c     d   e     f   g   h    i    j    k    l    m
            n    o    p     q   r     s   t   u    v    w    x    y    z
    the 10 decimal digits
            0    1    2     3   4     5   6   7    8    9
    the following 29 graphic characters
            !    "    #     %   &     '   (   )    *    +    ,    -    .    /    :
            ;    <    =     >   ?     [   \   ]    ^    _    {    |    }    ~
    the space character, and control characters representing horizontal tab, vertical tab, and
    form feed. The representation of each member of the source and execution basic
    character sets shall fit in a byte. In both the source and execution basic character sets, the
    value of each character after 0 in the above list of decimal digits shall be one greater than
    the value of the previous. In source files, there shall be some way of indicating the end of
    each line of text; this International Standard treats such an end-of-line indicator as if it
    were a single new-line character. In the basic execution character set, there shall be
    control characters representing alert, backspace, carriage return, and new line. If any
    other characters are encountered in a source file (except in an identifier, a character
    constant, a string literal, a header name, a comment, or a preprocessing token that is never

    converted to a token), the behavior is undefined.
4   A letter is an uppercase letter or a lowercase letter as defined above; in this International
    Standard the term does not include other characters that are letters in other alphabets.
5   The universal character name construct provides a way to name other characters.
    Forward references: universal character names (6.4.3), character constants (6.4.4.4),
    preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).

5.2.1.1 [Trigraph sequences]


1   Before any other processing takes place, each occurrence of one of the following
    sequences of three characters (called trigraph sequences17)) is replaced with the
    corresponding single character.
           ??=      #                       ??)      ]                       ??!      |
           ??(      [                       ??'      ^                       ??>      }
           ??/      \                       ??<      {                       ??-      ~
    No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
    above is not changed.
Footnote 17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
        described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.
2   EXAMPLE 1
              ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
    becomes
              #define arraycheck(a, b) a[b] || b[a]

3   EXAMPLE 2       The following source line
              printf("Eh???/n");
    becomes (after replacement of the trigraph sequence ??/)
              printf("Eh?\n");


5.2.1.2 [Multibyte characters]


1   The source character set may contain multibyte characters, used to represent members of
    the extended character set. The execution character set may also contain multibyte
    characters, which need not have the same encoding as for the source character set. For
    both character sets, the following shall hold:
    -- The basic character set shall be present and each character shall be encoded as a
       single byte.
    -- The presence, meaning, and representation of any additional members is locale-
       specific.

    -- A multibyte character set may have a state-dependent encoding, wherein each
       sequence of multibyte characters begins in an initial shift state and enters other
       locale-specific shift states when specific multibyte characters are encountered in the
       sequence. While in the initial shift state, all single-byte characters retain their usual
       interpretation and do not alter the shift state. The interpretation for subsequent bytes
       in the sequence is a function of the current shift state.
    -- A byte with all bits zero shall be interpreted as a null character independent of shift
       state. Such a byte shall not occur as part of any other multibyte character.
2   For source files, the following shall hold:
    -- An identifier, comment, string literal, character constant, or header name shall begin
       and end in the initial shift state.
    -- An identifier, comment, string literal, character constant, or header name shall consist
       of a sequence of valid multibyte characters.

5.2.2 [Character display semantics]


1   The active position is that location on a display device where the next character output by
    the fputc function would appear. The intent of writing a printing character (as defined
    by the isprint function) to a display device is to display a graphic representation of
    that character at the active position and then advance the active position to the next
    position on the current line. The direction of writing is locale-specific. If the active
    position is at the final position of a line (if there is one), the behavior of the display device
    is unspecified.
2   Alphabetic escape sequences representing nongraphic characters in the execution
    character set are intended to produce actions on display devices as follows:
    \a ( alert ) Produces an audible or visible alert without changing the active position.
    \b (backspace) Moves the active position to the previous position on the current line. If
       the active position is at the initial position of a line, the behavior of the display
       device is unspecified.
    \f ( form feed ) Moves the active position to the initial position at the start of the next
       logical page.
    \n ( new line) Moves the active position to the initial position of the next line.
    \r (carriage return) Moves the active position to the initial position of the current line.
    \t ( horizontal tab) Moves the active position to the next horizontal tabulation position
       on the current line. If the active position is at or past the last defined horizontal
       tabulation position, the behavior of the display device is unspecified.
    \v (vertical tab) Moves the active position to the initial position of the next vertical
       tabulation position. If the active position is at or past the last defined vertical
         tabulation position, the behavior of the display device is unspecified.
3   Each of these escape sequences shall produce a unique implementation-defined value
    which can be stored in a single char object. The external representations in a text file
    need not be identical to the internal representations, and are outside the scope of this
    International Standard.
    Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).

5.2.3 [Signals and interrupts]


1   Functions shall be implemented such that they may be interrupted at any time by a signal,
    or may be called by a signal handler, or both, with no alteration to earlier, but still active,
    invocations' control flow (after the interruption), function return values, or objects with
    automatic storage duration. All such objects shall be maintained outside the function
    image (the instructions that compose the executable representation of a function) on a
    per-invocation basis.

5.2.4 [Environmental limits]


1   Both the translation and execution environments constrain the implementation of
    language translators and libraries. The following summarizes the language-related
    environmental limits on a conforming implementation; the library-related limits are
    discussed in clause 7.

5.2.4.1 [Translation limits]


1   The implementation shall be able to translate and execute at least one program that
    contains at least one instance of every one of the following limits:18)
    -- 127 nesting levels of blocks
    -- 63 nesting levels of conditional inclusion
    -- 12 pointer, array, and function declarators (in any combinations) modifying an
       arithmetic, structure, union, or void type in a declaration
    -- 63 nesting levels of parenthesized declarators within a full declarator
    -- 63 nesting levels of parenthesized expressions within a full expression
    -- 63 significant initial characters in an internal identifier or a macro name (each
       universal character name or extended source character is considered a single
       character)
    -- 31 significant initial characters in an external identifier (each universal character name
       specifying a short identifier of 0000FFFF or less is considered 6 characters, each

         universal character name specifying a short identifier of 00010000 or more is
         considered 10 characters, and each extended source character is considered the same
         number of characters as the corresponding universal character name, if any)19)
    -- 4095 external identifiers in one translation unit
    -- 511 identifiers with block scope declared in one block
    -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
    -- 127 parameters in one function definition
    -- 127 arguments in one function call
    -- 127 parameters in one macro definition
    -- 127 arguments in one macro invocation
    -- 4095 characters in a logical source line
    -- 4095 characters in a string literal (after concatenation)
    -- 65535 bytes in an object (in a hosted environment only)
    -- 15 nesting levels for #included files
    -- 1023 case labels for a switch statement (excluding those for any nested switch
       statements)
    -- 1023 members in a single structure or union
    -- 1023 enumeration constants in a single enumeration
    -- 63 levels of nested structure or union definitions in a single struct-declaration-list
Footnote 19) See ``future language directions'' (6.11.3).

5.2.4.2 [Numerical limits]


1   An implementation is required to document all the limits specified in this subclause,
    which are specified in the headers <limits.h> and <float.h>. Additional limits are
    specified in <stdint.h>.
    Forward references: integer types <stdint.h> (7.20).

5.2.4.2.1 [Sizes of integer types ]


1   The values given below shall be replaced by constant expressions suitable for use in #if
    preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
    following shall be replaced by expressions that have the same type as would an
    expression that is an object of the corresponding type converted according to the integer
    promotions. Their implementation-defined values shall be equal or greater in magnitude

    (absolute value) to those shown, with the same sign.
    -- number of bits for smallest object that is not a bit-field (byte)
       CHAR_BIT                                            8
    -- minimum value for an object of type signed char
       SCHAR_MIN                                -127 // -(27 - 1)
    -- maximum value for an object of type signed char
       SCHAR_MAX                                +127 // 27 - 1
    -- maximum value for an object of type unsigned char
       UCHAR_MAX                                 255 // 28 - 1
    -- minimum value for an object of type char
       CHAR_MIN                               see below
    -- maximum value for an object of type char
       CHAR_MAX                              see below
    -- maximum number of bytes in a multibyte character, for any supported locale
       MB_LEN_MAX                                    1
    -- minimum value for an object of type short int
       SHRT_MIN                               -32767 // -(215 - 1)
    -- maximum value for an object of type short int
       SHRT_MAX                               +32767 // 215 - 1
    -- maximum value for an object of type unsigned short int
       USHRT_MAX                               65535 // 216 - 1
    -- minimum value for an object of type int
       INT_MIN                                 -32767 // -(215 - 1)
    -- maximum value for an object of type int
       INT_MAX                                +32767 // 215 - 1
    -- maximum value for an object of type unsigned int
       UINT_MAX                                65535 // 216 - 1
    -- minimum value for an object of type long int
       LONG_MIN                         -2147483647 // -(231 - 1)
    -- maximum value for an object of type long int
       LONG_MAX                         +2147483647 // 231 - 1
    -- maximum value for an object of type unsigned long int
       ULONG_MAX                         4294967295 // 232 - 1
    -- minimum value for an object of type long long int
       LLONG_MIN          -9223372036854775807 // -(263 - 1)
    -- maximum value for an object of type long long int
       LLONG_MAX          +9223372036854775807 // 263 - 1
    -- maximum value for an object of type unsigned long long int
       ULLONG_MAX         18446744073709551615 // 264 - 1
2   If the value of an object of type char is treated as a signed integer when used in an
    expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
    value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
    CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
    UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1.
    Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).
Footnote 20) See 6.2.5.

5.2.4.2.2 [Characteristics of floating types ]


1   The characteristics of floating types are defined in terms of a model that describes a
    representation of floating-point numbers and values that provide information about an
    implementation's floating-point arithmetic.21) The following parameters are used to
    define the model for each floating-point type:
           s          sign (±1)
           b          base or radix of exponent representation (an integer > 1)
           e          exponent (an integer between a minimum emin and a maximum emax )
           p          precision (the number of base-b digits in the significand)
            fk        nonnegative integers less than b (the significand digits)
Footnote 21) The floating-point model is intended to clarify the description of each floating-point characteristic and
        does not require the floating-point arithmetic of the implementation to be identical.
2   A floating-point number ( x ) is defined by the following model:
                       p
           x = sb e
                      k =1
                           f k b-k ,   emin  e  emax

3   In addition to normalized floating-point numbers ( f 1 > 0 if x  0), floating types may be
    able to contain other kinds of floating-point numbers, such as subnormal floating-point
    numbers ( x  0, e = emin , f 1 = 0) and unnormalized floating-point numbers ( x  0,
    e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
    NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
    through almost every arithmetic operation without raising a floating-point exception; a
    signaling NaN generally raises a floating-point exception when occurring as an

    arithmetic operand.22)
Footnote 22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
        IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
        similar behavior.
4   An implementation may give zero and values that are not floating-point numbers (such as
    infinities and NaNs) a sign or may leave them unsigned. Wherever such values are
    unsigned, any requirement in this International Standard to retrieve the sign shall produce
    an unspecified sign, and any requirement to set the sign shall be ignored.
5   The minimum range of representable values for a floating type is the most negative finite
    floating-point number representable in that type through the most positive finite floating-
    point number representable in that type. In addition, if negative infinity is representable
    in a type, the range of that type is extended to all negative real numbers; likewise, if
    positive infinity is representable in a type, the range of that type is extended to all positive
    real numbers.
6   The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
    <math.h> and <complex.h> that return floating-point results is implementation-
    defined, as is the accuracy of the conversion between floating-point internal
    representations and string representations performed by the library functions in
    <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
    accuracy is unknown.
7   All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
    expressions suitable for use in #if preprocessing directives; all floating values shall be
    constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
    and FLT_ROUNDS have separate names for all three floating-point types. The floating-
    point model representation is provided for all values except FLT_EVAL_METHOD and
    FLT_ROUNDS.
8   The rounding mode for floating-point addition is characterized by the implementation-
    defined value of FLT_ROUNDS:23)
          -1      indeterminable
           0      toward zero
           1      to nearest
           2      toward positive infinity
           3      toward negative infinity
    All other values for FLT_ROUNDS characterize implementation-defined rounding
    behavior.

Footnote 23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
        the function fesetround in <fenv.h>.
9    Except for assignment and cast (which remove all extra range and precision), the values
     yielded by operators with floating operands and values subject to the usual arithmetic
     conversions and of floating constants are evaluated to a format whose range and precision
     may be greater than required by the type. The use of evaluation formats is characterized
     by the implementation-defined value of FLT_EVAL_METHOD:24)
            -1         indeterminable;
              0        evaluate all operations and constants just to the range and precision of the
                       type;
              1        evaluate operations and constants of type float and double to the
                       range and precision of the double type, evaluate long double
                       operations and constants to the range and precision of the long double
                       type;
              2        evaluate all operations and constants to the range and precision of the
                       long double type.
     All other negative values for FLT_EVAL_METHOD characterize implementation-defined
     behavior.
Footnote 24) The evaluation method determines evaluation formats of expressions involving all floating types, not
         just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
         _Complex operands is represented in the double _Complex format, and its parts are evaluated to
         double.
10   The presence or absence of subnormal numbers is characterized by the implementation-
     defined    values     of    FLT_HAS_SUBNORM,          DBL_HAS_SUBNORM,           and
     LDBL_HAS_SUBNORM:
            -1       indeterminable25)
             0       absent26) (type does not support subnormal numbers)
             1       present (type does support subnormal numbers)
Footnote 25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
         subnormal representations as zero, nor as nonzero.
Footnote 26) Characterization as absent is intended if no floating-point operations produce subnormal results from
         non-subnormal inputs, even if the type format includes representations of subnormal numbers.
11   The values given in the following list shall be replaced by constant expressions with
     implementation-defined values that are greater or equal in magnitude (absolute value) to
     those shown, with the same sign:
     -- radix of exponent representation, b
        FLT_RADIX                                                    2

      -- number of base-FLT_RADIX digits in the floating-point significand, p
         FLT_MANT_DIG
         DBL_MANT_DIG
         LDBL_MANT_DIG
      -- number of decimal digits, n, such that any floating-point number with p radix b digits
         can be rounded to a floating-point number with n decimal digits and back again
         without change to the value,
               p log10 b         if b is a power of 10
              
               1 + p log10 b otherwise
         FLT_DECIMAL_DIG                                    6
         DBL_DECIMAL_DIG                                   10
         LDBL_DECIMAL_DIG                                  10
      -- number of decimal digits, n, such that any floating-point number in the widest
         supported floating type with pmax radix b digits can be rounded to a floating-point
         number with n decimal digits and back again without change to the value,
               pmax log10 b        if b is a power of 10
              
               1 + pmax log10 b otherwise
         DECIMAL_DIG                                      10
      -- number of decimal digits, q , such that any floating-point number with q decimal digits
         can be rounded into a floating-point number with p radix b digits and back again
         without change to the q decimal digits,
               p log10 b          if b is a power of 10
              
               ( p - 1) log10 b otherwise
         FLT_DIG                                           6
         DBL_DIG                                          10
         LDBL_DIG                                         10
      -- minimum negative integer such that FLT_RADIX raised to one less than that power is
         a normalized floating-point number, emin
         FLT_MIN_EXP
         DBL_MIN_EXP
         LDBL_MIN_EXP
           -- minimum negative integer such that 10 raised to that power is in the range of
              normalized floating-point numbers, log10 b emin -1 
                                                                 
              FLT_MIN_10_EXP                                 -37
              DBL_MIN_10_EXP                                 -37
              LDBL_MIN_10_EXP                                -37
     -- maximum integer such that FLT_RADIX raised to one less than that power is a
        representable finite floating-point number, emax
          FLT_MAX_EXP
          DBL_MAX_EXP
          LDBL_MAX_EXP
     -- maximum integer such that 10 raised to that power is in the range of representable
        finite floating-point numbers, log10 ((1 - b- p )b emax )
          FLT_MAX_10_EXP                                +37
          DBL_MAX_10_EXP                                +37
          LDBL_MAX_10_EXP                               +37
12   The values given in the following list shall be replaced by constant expressions with
     implementation-defined values that are greater than or equal to those shown:
     -- maximum representable finite floating-point number, (1 - b- p )b emax
          FLT_MAX                                    1E+37
          DBL_MAX                                    1E+37
          LDBL_MAX                                   1E+37
13   The values given in the following list shall be replaced by constant expressions with
     implementation-defined (positive) values that are less than or equal to those shown:
     -- the difference between 1 and the least value greater than 1 that is representable in the
        given floating point type, b1- p
          FLT_EPSILON                                 1E-5
          DBL_EPSILON                                 1E-9
          LDBL_EPSILON                                1E-9
     -- minimum normalized positive floating-point number, b emin -1
          FLT_MIN                                    1E-37
          DBL_MIN                                    1E-37
          LDBL_MIN                                   1E-37
     -- minimum positive floating-point number27)
         FLT_TRUE_MIN                                        1E-37
         DBL_TRUE_MIN                                        1E-37
         LDBL_TRUE_MIN                                       1E-37
     Recommended practice
Footnote 27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
         positive number no greater than the minimum normalized positive number for the type.
14   Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
     should be the identity function.
15   EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
     requirements of this International Standard, and the appropriate values in a <float.h> header for type
     float:
                         6
           x = s16e
                        k =1
                             f k 16-k ,    -31  e  +32

             FLT_RADIX                                        16
             FLT_MANT_DIG                                      6
             FLT_EPSILON                         9.53674316E-07F
             FLT_DECIMAL_DIG                                   9
             FLT_DIG                                           6
             FLT_MIN_EXP                                     -31
             FLT_MIN                             2.93873588E-39F
             FLT_MIN_10_EXP                                  -38
             FLT_MAX_EXP                                     +32
             FLT_MAX                             3.40282347E+38F
             FLT_MAX_10_EXP                                  +38

16   EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
     single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a
     <float.h> header for types float and double:
                        24
           x f = s 2e
                        k =1
                             f k 2-k ,    -125  e  +128

                        53
           x d = s 2e
                        k =1
                             f k 2-k ,    -1021  e  +1024

             FLT_RADIX                                         2
             DECIMAL_DIG                                      17
             FLT_MANT_DIG                                     24
             FLT_EPSILON                         1.19209290E-07F // decimal constant
             FLT_EPSILON                                0X1P-23F // hex constant
             FLT_DECIMAL_DIG                                   9

        FLT_DIG                             6
        FLT_MIN_EXP                      -125
        FLT_MIN               1.17549435E-38F               //   decimal constant
        FLT_MIN                     0X1P-126F               //   hex constant
        FLT_TRUE_MIN          1.40129846E-45F               //   decimal constant
        FLT_TRUE_MIN                0X1P-149F               //   hex constant
        FLT_HAS_SUBNORM                     1
        FLT_MIN_10_EXP                    -37
        FLT_MAX_EXP                      +128
        FLT_MAX               3.40282347E+38F               // decimal constant
        FLT_MAX               0X1.fffffeP127F               // hex constant
        FLT_MAX_10_EXP                    +38
        DBL_MANT_DIG                       53
        DBL_EPSILON    2.2204460492503131E-16               // decimal constant
        DBL_EPSILON                   0X1P-52               // hex constant
        DBL_DECIMAL_DIG                    17
        DBL_DIG                            15
        DBL_MIN_EXP                     -1021
        DBL_MIN      2.2250738585072014E-308                //   decimal constant
        DBL_MIN                     0X1P-1022               //   hex constant
        DBL_TRUE_MIN 4.9406564584124654E-324                //   decimal constant
        DBL_TRUE_MIN                0X1P-1074               //   hex constant
        DBL_HAS_SUBNORM                     1
        DBL_MIN_10_EXP                   -307
        DBL_MAX_EXP                     +1024
        DBL_MAX      1.7976931348623157E+308                // decimal constant
        DBL_MAX        0X1.fffffffffffffP1023               // hex constant
        DBL_MAX_10_EXP                   +308
If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
precision), then DECIMAL_DIG would be 21.

Forward references:         conditional inclusion (6.10.1), complex arithmetic
<complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
(7.29), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
(7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).

Footnote 28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
         limits are one less than shown here.

6. [Language]

 Language

6.1 [Notation]


1   In the syntax notation used in this clause, syntactic categories (nonterminals) are
    indicated by italic type, and literal words and character set members (terminals) by bold
    type. A colon (:) following a nonterminal introduces its definition. Alternative
    definitions are listed on separate lines, except when prefaced by the words ``one of''. An
    optional symbol is indicated by the subscript ``opt'', so that
             { expressionopt }
    indicates an optional expression enclosed in braces.
2   When syntactic categories are referred to in the main text, they are not italicized and
    words are separated by spaces instead of hyphens.
3   A summary of the language syntax is given in annex A.

6.2 [Concepts]

 Concepts

6.2.1 [Scopes of identifiers]


1   An identifier can denote an object; a function; a tag or a member of a structure, union, or
    enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
    same identifier can denote different entities at different points in the program. A member
    of an enumeration is called an enumeration constant . Macro names and macro
    parameters are not considered further here, because prior to the semantic phase of
    program translation any occurrences of macro names in the source file are replaced by the
    preprocessing token sequences that constitute their macro definitions.
2   For each different entity that an identifier designates, the identifier is visible (i.e., can be
    used) only within a region of program text called its scope. Different entities designated
    by the same identifier either have different scopes, or are in different name spaces. There
    are four kinds of scopes: function, file, block, and function prototype. (A function
    prototype is a declaration of a function that declares the types of its parameters.)
3   A label name is the only kind of identifier that has function scope. It can be used (in a
    goto statement) anywhere in the function in which it appears, and is declared implicitly
    by its syntactic appearance (followed by a : and a statement).
4   Every other identifier has scope determined by the placement of its declaration (in a
    declarator or type specifier). If the declarator or type specifier that declares the identifier
    appears outside of any block or list of parameters, the identifier has file scope, which
    terminates at the end of the translation unit. If the declarator or type specifier that
    declares the identifier appears inside a block or within the list of parameter declarations in
    a function definition, the identifier has block scope, which terminates at the end of the
    associated block. If the declarator or type specifier that declares the identifier appears

    within the list of parameter declarations in a function prototype (not part of a function
    definition), the identifier has function prototype scope, which terminates at the end of the
    function declarator. If an identifier designates two different entities in the same name
    space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
    strictly before the scope of the other entity (the outer scope). Within the inner scope, the
    identifier designates the entity declared in the inner scope; the entity declared in the outer
    scope is hidden (and not visible) within the inner scope.
5   Unless explicitly stated otherwise, where this International Standard uses the term
    ``identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the
    entity in the relevant name space whose declaration is visible at the point the identifier
    occurs.
6   Two identifiers have the same scope if and only if their scopes terminate at the same
    point.
7   Structure, union, and enumeration tags have scope that begins just after the appearance of
    the tag in a type specifier that declares the tag. Each enumeration constant has scope that
    begins just after the appearance of its defining enumerator in an enumerator list. Any
    other identifier has scope that begins just after the completion of its declarator.
8   As a special case, a type name (which is not a declaration of an identifier) is considered to
    have a scope that begins just after the place within the type name where the omitted
    identifier would appear were it not omitted.
    Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
    (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
    source file inclusion (6.10.2), statements (6.8).

6.2.2 [Linkages of identifiers]


1   An identifier declared in different scopes or in the same scope more than once can be
    made to refer to the same object or function by a process called linkage.29) There are
    three kinds of linkage: external, internal, and none.
Footnote 29) There is no linkage between different identifiers.
2   In the set of translation units and libraries that constitutes an entire program, each
    declaration of a particular identifier with external linkage denotes the same object or
    function. Within one translation unit, each declaration of an identifier with internal
    linkage denotes the same object or function. Each declaration of an identifier with no
    linkage denotes a unique entity.
3   If the declaration of a file scope identifier for an object or a function contains the storage-
    class specifier static, the identifier has internal linkage.30)

Footnote 30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
        6.7.1.
4   For an identifier declared with the storage-class specifier extern in a scope in which a
    prior declaration of that identifier is visible,31) if the prior declaration specifies internal or
    external linkage, the linkage of the identifier at the later declaration is the same as the
    linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
    declaration specifies no linkage, then the identifier has external linkage.
Footnote 31) As specified in 6.2.1, the later declaration might hide the prior declaration.
5   If the declaration of an identifier for a function has no storage-class specifier, its linkage
    is determined exactly as if it were declared with the storage-class specifier extern. If
    the declaration of an identifier for an object has file scope and no storage-class specifier,
    its linkage is external.
6   The following identifiers have no linkage: an identifier declared to be anything other than
    an object or a function; an identifier declared to be a function parameter; a block scope
    identifier for an object declared without the storage-class specifier extern.
7   If, within a translation unit, the same identifier appears with both internal and external
    linkage, the behavior is undefined.
    Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
    statements (6.8).

6.2.3 [Name spaces of identifiers]


1   If more than one declaration of a particular identifier is visible at any point in a
    translation unit, the syntactic context disambiguates uses that refer to different entities.
    Thus, there are separate name spaces for various categories of identifiers, as follows:
    -- label names (disambiguated by the syntax of the label declaration and use);
    -- the tags of structures, unions, and enumerations (disambiguated by following any32)
       of the keywords struct, union, or enum);
    -- the members of structures or unions; each structure or union has a separate name
       space for its members (disambiguated by the type of the expression used to access the
       member via the . or -> operator);
    -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
       enumeration constants).
    Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
    structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
    (6.7.2.3), the goto statement (6.8.6.1).


6.2.4 [Storage durations of objects]


1   An object has a storage duration that determines its lifetime. There are four storage
    durations: static, thread, automatic, and allocated. Allocated storage is described in 7.22.3.
2   The lifetime of an object is the portion of program execution during which storage is
    guaranteed to be reserved for it. An object exists, has a constant address,33) and retains
    its last-stored value throughout its lifetime.34) If an object is referred to outside of its
    lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
    the object it points to (or just past) reaches the end of its lifetime.
Footnote 33) The term ``constant address'' means that two pointers to the object constructed at possibly different
        times will compare equal. The address may be different during two different executions of the same
        program.
Footnote 34) In the case of a volatile object, the last store need not be explicit in the program.
3   An object whose identifier is declared without the storage-class specifier
    _Thread_local, and either with external or internal linkage or with the storage-class
    specifier static, has static storage duration. Its lifetime is the entire execution of the
    program and its stored value is initialized only once, prior to program startup.
4   An object whose identifier is declared with the storage-class specifier _Thread_local
    has thread storage duration. Its lifetime is the entire execution of the thread for which it
    is created, and its stored value is initialized when the thread is started. There is a distinct
    object per thread, and use of the declared name in an expression refers to the object
    associated with the thread evaluating the expression. The result of attempting to
    indirectly access an object with thread storage duration from a thread other than the one
    with which the object is associated is implementation-defined.
5   An object whose identifier is declared with no linkage and without the storage-class
    specifier static has automatic storage duration, as do some compound literals. The
    result of attempting to indirectly access an object with automatic storage duration from a
    thread other than the one with which the object is associated is implementation-defined.
6   For such an object that does not have a variable length array type, its lifetime extends
    from entry into the block with which it is associated until execution of that block ends in
    any way. (Entering an enclosed block or calling a function suspends, but does not end,
    execution of the current block.) If the block is entered recursively, a new instance of the
    object is created each time. The initial value of the object is indeterminate. If an
    initialization is specified for the object, it is performed each time the declaration or
    compound literal is reached in the execution of the block; otherwise, the value becomes
    indeterminate each time the declaration is reached.

7   For such an object that does have a variable length array type, its lifetime extends from
    the declaration of the object until execution of the program leaves the scope of the
    declaration.35) If the scope is entered recursively, a new instance of the object is created
    each time. The initial value of the object is indeterminate.
Footnote 35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
        embedded block prior to the declaration, leaves the scope of the declaration.
8   A non-lvalue expression with structure or union type, where the structure or union
    contains a member with array type (including, recursively, members of all contained
    structures and unions) refers to an object with automatic storage duration and temporary
    lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the
    value of the expression. Its lifetime ends when the evaluation of the containing full
    expression or full declarator ends. Any attempt to modify an object with temporary
    lifetime results in undefined behavior.
    Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
    (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).
Footnote 36) The address of such an object is taken implicitly when an array member is accessed.

6.2.5 [Types]


1   The meaning of a value stored in an object or returned by a function is determined by the
    type of the expression used to access it. (An identifier declared to be an object is the
    simplest such expression; the type is specified in the declaration of the identifier.) Types
    are partitioned into object types (types that describe objects) and function types (types
    that describe functions). At various points within a translation unit an object type may be
    incomplete (lacking sufficient information to determine the size of objects of that type) or
    complete (having sufficient information).37)
Footnote 37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
        different points within a translation unit.
2   An object declared as type _Bool is large enough to store the values 0 and 1.
3   An object declared as type char is large enough to store any member of the basic
    execution character set. If a member of the basic execution character set is stored in a
    char object, its value is guaranteed to be nonnegative. If any other character is stored in
    a char object, the resulting value is implementation-defined but shall be within the range
    of values that can be represented in that type.
4   There are five standard signed integer types, designated as signed char, short
    int, int, long int, and long long int. (These and other types may be
    designated in several additional ways, as described in 6.7.2.) There may also be
    implementation-defined extended signed integer types.38) The standard and extended
    signed integer types are collectively called signed integer types.39)

Footnote 38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
         described in 7.1.3.
Footnote 39) Therefore, any statement in this Standard about signed integer types also applies to the extended
         signed integer types.
5    An object declared as type signed char occupies the same amount of storage as a
     ``plain'' char object. A ``plain'' int object has the natural size suggested by the
     architecture of the execution environment (large enough to contain any value in the range
     INT_MIN to INT_MAX as defined in the header <limits.h>).
6    For each of the signed integer types, there is a corresponding (but different) unsigned
     integer type (designated with the keyword unsigned) that uses the same amount of
     storage (including sign information) and has the same alignment requirements. The type
     _Bool and the unsigned integer types that correspond to the standard signed integer
     types are the standard unsigned integer types. The unsigned integer types that
     correspond to the extended signed integer types are the extended unsigned integer types.
     The standard and extended unsigned integer types are collectively called unsigned integer
     types.40)
Footnote 40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
         unsigned integer types.
7    The standard signed integer types and standard unsigned integer types are collectively
     called the standard integer types, the extended signed integer types and extended
     unsigned integer types are collectively called the extended integer types.
8    For any two integer types with the same signedness and different integer conversion rank
     (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
     subrange of the values of the other type.
9    The range of nonnegative values of a signed integer type is a subrange of the
     corresponding unsigned integer type, and the representation of the same value in each
     type is the same.41) A computation involving unsigned operands can never overflow,
     because a result that cannot be represented by the resulting unsigned integer type is
     reduced modulo the number that is one greater than the largest value that can be
     represented by the resulting type.
Footnote 41) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.
10   There are three real floating types, designated as float, double, and long
     double.42) The set of values of the type float is a subset of the set of values of the
     type double; the set of values of the type double is a subset of the set of values of the
     type long double.

Footnote 42) See ``future language directions'' (6.11.1).
11   There are three complex types, designated as float _Complex, double
     _Complex, and long double _Complex.43) (Complex types are a conditional
     feature that implementations need not support; see 6.10.8.3.) The real floating and
     complex types are collectively called the floating types.
Footnote 43) A specification for imaginary types is in annex G.
12   For each floating type there is a corresponding real type, which is always a real floating
     type. For real floating types, it is the same type. For complex types, it is the type given
     by deleting the keyword _Complex from the type name.
13   Each complex type has the same representation and alignment requirements as an array
     type containing exactly two elements of the corresponding real type; the first element is
     equal to the real part, and the second element to the imaginary part, of the complex
     number.
14   The type char, the signed and unsigned integer types, and the floating types are
     collectively called the basic types. The basic types are complete object types. Even if the
     implementation defines two or more basic types to have the same representation, they are
     nevertheless different types.44)
Footnote 44) An implementation may define new keywords that provide alternative ways to designate a basic (or
         any other) type; this does not violate the requirement that all basic types be different.
         Implementation-defined keywords shall have the form of an identifier reserved for any use as
         described in 7.1.3.
15   The three types char, signed char, and unsigned char are collectively called
     the character types. The implementation shall define char to have the same range,
     representation, and behavior as either signed char or unsigned char.45)
Footnote 45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be
         used to distinguish the two options. Irrespective of the choice made, char is a separate type from the
         other two and is not compatible with either.
16   An enumeration comprises a set of named integer constant values. Each distinct
     enumeration constitutes a different enumerated type.
17   The type char, the signed and unsigned integer types, and the enumerated types are
     collectively called integer types. The integer and real floating types are collectively called
     real types.
18   Integer and floating types are collectively called arithmetic types. Each arithmetic type
     belongs to one type domain: the real type domain comprises the real types, the complex
     type domain comprises the complex types.
19   The void type comprises an empty set of values; it is an incomplete object type that
     cannot be completed.

20   Any number of derived types can be constructed from the object and function types, as
     follows:
     -- An array type describes a contiguously allocated nonempty set of objects with a
        particular member object type, called the element type. The element type shall be
        complete whenever the array type is specified. Array types are characterized by their
        element type and by the number of elements in the array. An array type is said to be
        derived from its element type, and if its element type is T , the array type is sometimes
        called ``array of T ''. The construction of an array type from an element type is called
        ``array type derivation''.
     -- A structure type describes a sequentially allocated nonempty set of member objects
        (and, in certain circumstances, an incomplete array), each of which has an optionally
        specified name and possibly distinct type.
     -- A union type describes an overlapping nonempty set of member objects, each of
        which has an optionally specified name and possibly distinct type.
     -- A function type describes a function with specified return type. A function type is
        characterized by its return type and the number and types of its parameters. A
        function type is said to be derived from its return type, and if its return type is T , the
        function type is sometimes called ``function returning T ''. The construction of a
        function type from a return type is called ``function type derivation''.
     -- A pointer type may be derived from a function type or an object type, called the
        referenced type. A pointer type describes an object whose value provides a reference
        to an entity of the referenced type. A pointer type derived from the referenced type T
        is sometimes called ``pointer to T ''. The construction of a pointer type from a
        referenced type is called ``pointer type derivation''. A pointer type is a complete
        object type.
     -- An atomic type describes the type designated by the construct _Atomic ( type-
        name ). (Atomic types are a conditional feature that implementations need not
        support; see 6.10.8.3.)
     These methods of constructing derived types can be applied recursively.
21   Arithmetic types and pointer types are collectively called scalar types. Array and
     structure types are collectively called aggregate types.46)
Footnote 46) Note that aggregate type does not include union type because an object with union type can only
         contain one member at a time.
22   An array type of unknown size is an incomplete type. It is completed, for an identifier of
     that type, by specifying the size in a later declaration (with internal or external linkage).
     A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete

     type. It is completed, for all declarations of that type, by declaring the same structure or
     union tag with its defining content later in the same scope.
23   A type has known constant size if the type is not incomplete and is not a variable length
     array type.
24   Array, function, and pointer types are collectively called derived declarator types. A
     declarator type derivation from a type T is the construction of a derived declarator type
     from T by the application of an array-type, a function-type, or a pointer-type derivation to
     T.
25   A type is characterized by its type category , which is either the outermost derivation of a
     derived type (as noted above in the construction of derived types), or the type itself if the
     type consists of no derived types.
26   Any type so far mentioned is an unqualified type. Each unqualified type has several
     qualified versions of its type,47) corresponding to the combinations of one, two, or all
     three of the const, volatile, and restrict qualifiers. The qualified or unqualified
     versions of a type are distinct types that belong to the same type category and have the
     same representation and alignment requirements.48) A derived type is not qualified by the
     qualifiers (if any) of the type from which it is derived.
Footnote 47) See 6.7.3 regarding qualified array and function types.
Footnote 48) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.
27   Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier
     designates an atomic type. The size, representation, and alignment of an atomic type
     need not be the same as those of the corresponding unqualified type. Therefore, this
     Standard explicitly uses the phrase ``atomic, qualified or unqualified type'' whenever the
     atomic version of a type is permitted along with the other qualified versions of a type.
     The phrase ``qualified or unqualified type'', without specific mention of atomic, does not
     include the atomic types.
28   A pointer to void shall have the same representation and alignment requirements as a
     pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of
     compatible types shall have the same representation and alignment requirements. All
     pointers to structure types shall have the same representation and alignment requirements
     as each other. All pointers to union types shall have the same representation and
     alignment requirements as each other. Pointers to other types need not have the same
     representation or alignment requirements.
Footnote 48) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.
29   EXAMPLE 1 The type designated as ``float *'' has type ``pointer to float''. Its type category is
     pointer, not a floating type. The const-qualified version of this type is designated as ``float * const''
     whereas the type designated as ``const float *'' is not a qualified type -- its type is ``pointer to const-

     qualified float'' and is a pointer to a qualified type.

30   EXAMPLE 2 The type designated as ``struct tag (*[5])(float)'' has type ``array of pointer to
     function returning struct tag''. The array has length five and the function has a single parameter of type
     float. Its type category is array.

     Forward references: compatible type and composite type (6.2.7), declarations (6.7).

6.2.6 [Representations of types]

 Representations of types

6.2.6.1 [General]


1    The representations of all types are unspecified except as stated in this subclause.
2    Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
     the number, order, and encoding of which are either explicitly specified or
     implementation-defined.
3    Values stored in unsigned bit-fields and objects of type unsigned char shall be
     represented using a pure binary notation.49)
Footnote 49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
         represented by successive bits are additive, begin with 1, and are multiplied by successive integral
         powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
         Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
         type unsigned char range from 0 to 2
                                                   CHAR_BIT
                                                             - 1.
4    Values stored in non-bit-field objects of any other object type consist of n × CHAR_BIT
     bits, where n is the size of an object of that type, in bytes. The value may be copied into
     an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
     called the object representation of the value. Values stored in bit-fields consist of m bits,
     where m is the size specified for the bit-field. The object representation is the set of m
     bits the bit-field comprises in the addressable storage unit holding it. Two values (other
     than NaNs) with the same object representation compare equal, but values that compare
     equal may have different object representations.
5    Certain object representations need not represent a value of the object type. If the stored
     value of an object has such a representation and is read by an lvalue expression that does
     not have character type, the behavior is undefined. If such a representation is produced
     by a side effect that modifies all or any part of the object by an lvalue expression that
     does not have character type, the behavior is undefined.50) Such a representation is called
     a trap representation.
Footnote 50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
         behavior, but the value of the variable cannot be used until a proper value is stored in it.
6    When a value is stored in an object of structure or union type, including in a member
     object, the bytes of the object representation that correspond to any padding bytes take
     unspecified values.51) The value of a structure or union object is never a trap

    representation, even though the value of a member of the structure or union object may be
    a trap representation.
Footnote 51) Thus, for example, structure assignment need not copy any padding bits.
7   When a value is stored in a member of an object of union type, the bytes of the object
    representation that do not correspond to that member but do correspond to other members
    take unspecified values.
8   Where an operator is applied to a value that has more than one object representation,
    which object representation is used shall not affect the value of the result.52) Where a
    value is stored in an object using a type that has more than one object representation for
    that value, it is unspecified which representation is used, but a trap representation shall
    not be generated.
Footnote 52) It is possible for objects x and y with the same effective type T to have the same value when they are
        accessed as objects of type T, but to have different values in other contexts. In particular, if == is
        defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
        Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
        on values of type T may distinguish between them.
9   Loads and stores of objects with                             atomic      types      are     done      with
    memory_order_seq_cst semantics.
    Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
    designators (6.3.2.1), order and consistency (7.17.3).

6.2.6.2 [Integer types]


1   For unsigned integer types other than unsigned char, the bits of the object
    representation shall be divided into two groups: value bits and padding bits (there need
    not be any of the latter). If there are N value bits, each bit shall represent a different
    power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of
    representing values from 0 to 2 N - 1 using a pure binary representation; this shall be
    known as the value representation. The values of any padding bits are unspecified.53)
Footnote 53) Some combinations of padding bits might generate trap representations, for example, if one padding
        bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
        representation other than as part of an exceptional condition such as an overflow, and this cannot occur
        with unsigned types. All other combinations of padding bits are alternative object representations of
        the value specified by the value bits.
2   For signed integer types, the bits of the object representation shall be divided into three
    groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
    signed char shall not have any padding bits. There shall be exactly one sign bit.
    Each bit that is a value bit shall have the same value as the same bit in the object
    representation of the corresponding unsigned type (if there are M value bits in the signed
    type and N in the unsigned type, then M  N ). If the sign bit is zero, it shall not affect

    the resulting value. If the sign bit is one, the value shall be modified in one of the
    following ways:
    -- the corresponding value with sign bit 0 is negated (sign and magnitude);
    -- the sign bit has the value -(2 M ) (two's complement );
    -- the sign bit has the value -(2 M - 1) (ones' complement ).
    Which of these applies is implementation-defined, as is whether the value with sign bit 1
    and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones'
    complement), is a trap representation or a normal value. In the case of sign and
    magnitude and ones' complement, if this representation is a normal value it is called a
    negative zero.
3   If the implementation supports negative zeros, they shall be generated only by:
    -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
    -- the +, -, *, /, and % operators where one operand is a negative zero and the result is
       zero;
    -- compound assignment operators based on the above cases.
    It is unspecified whether these cases actually generate a negative zero or a normal zero,
    and whether a negative zero becomes a normal zero when stored in an object.
4   If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
    and >> operators with operands that would produce such a value is undefined.
5   The values of any padding bits are unspecified.54) A valid (non-trap) object representation
    of a signed integer type where the sign bit is zero is a valid object representation of the
    corresponding unsigned type, and shall represent the same value. For any integer type,
    the object representation where all the bits are zero shall be a representation of the value
    zero in that type.
Footnote 54) Some combinations of padding bits might generate trap representations, for example, if one padding
        bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
        representation other than as part of an exceptional condition such as an overflow. All other
        combinations of padding bits are alternative object representations of the value specified by the value
        bits.
6   The precision of an integer type is the number of bits it uses to represent values,
    excluding any sign and padding bits. The width of an integer type is the same but
    including any sign bit; thus for unsigned integer types the two values are the same, while
    for signed integer types the width is one greater than the precision.


6.2.7 [Compatible type and composite type]


1   Two types have compatible type if their types are the same. Additional rules for
    determining whether two types are compatible are described in 6.7.2 for type specifiers,
    in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure,
    union, or enumerated types declared in separate translation units are compatible if their
    tags and members satisfy the following requirements: If one is declared with a tag, the
    other shall be declared with the same tag. If both are completed anywhere within their
    respective translation units, then the following additional requirements apply: there shall
    be a one-to-one correspondence between their members such that each pair of
    corresponding members are declared with compatible types; if one member of the pair is
    declared with an alignment specifier, the other is declared with an equivalent alignment
    specifier; and if one member of the pair is declared with a name, the other is declared
    with the same name. For two structures, corresponding members shall be declared in the
    same order. For two structures or unions, corresponding bit-fields shall have the same
    widths. For two enumerations, corresponding members shall have the same values.
Footnote 55) Two types need not be identical to be compatible.
2   All declarations that refer to the same object or function shall have compatible type;
    otherwise, the behavior is undefined.
3   A composite type can be constructed from two types that are compatible; it is a type that
    is compatible with both of the two types and satisfies the following conditions:
    -- If both types are array types, the following rules are applied:
          ·   If one type is an array of known constant size, the composite type is an array of
              that size.
          ·   Otherwise, if one type is a variable length array whose size is specified by an
              expression that is not evaluated, the behavior is undefined.
          ·   Otherwise, if one type is a variable length array whose size is specified, the
              composite type is a variable length array of that size.
          ·   Otherwise, if one type is a variable length array of unspecified size, the composite
              type is a variable length array of unspecified size.
          ·   Otherwise, both types are arrays of unknown size and the composite type is an
              array of unknown size.
        The element type of the composite type is the composite type of the two element
        types.
    -- If only one type is a function type with a parameter type list (a function prototype),
       the composite type is a function prototype with the parameter type list.

    -- If both types are function types with parameter type lists, the type of each parameter
       in the composite parameter type list is the composite type of the corresponding
       parameters.
    These rules apply recursively to the types from which the two types are derived.
4   For an identifier with internal or external linkage declared in a scope in which a prior
    declaration of that identifier is visible,56) if the prior declaration specifies internal or
    external linkage, the type of the identifier at the later declaration becomes the composite
    type.
    Forward references: array declarators (6.7.6.2).
Footnote 56) As specified in 6.2.1, the later declaration might hide the prior declaration.
5   EXAMPLE        Given the following two file scope declarations:
             int f(int (*)(), double (*)[3]);
             int f(int (*)(char *), double (*)[]);
    The resulting composite type for the function is:
             int f(int (*)(char *), double (*)[3]);


6.2.8 [Alignment of objects]


1   Complete object types have alignment requirements which place restrictions on the
    addresses at which objects of that type may be allocated. An alignment is an
    implementation-defined integer value representing the number of bytes between
    successive addresses at which a given object can be allocated. An object type imposes an
    alignment requirement on every object of that type: stricter alignment can be requested
    using the _Alignas keyword.
2   A fundamental alignment is represented by an alignment less than or equal to the greatest
    alignment supported by the implementation in all contexts, which is equal to
    _Alignof (max_align_t).
3   An extended alignment is represented by an alignment greater than
    _Alignof (max_align_t). It is implementation-defined whether any extended
    alignments are supported and the contexts in which they are supported. A type having an
    extended alignment requirement is an over-aligned type.57)
Footnote 57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
        alignment has been applied.
4   Alignments are represented as values of the type size_t. Valid alignments include only
    those values returned by an _Alignof expression for fundamental types, plus an
    additional implementation-defined set of values, which may be empty. Every valid
    alignment value shall be a nonnegative integral power of two.

5   Alignments have an order from weaker to stronger or stricter alignments. Stricter
    alignments have larger alignment values. An address that satisfies an alignment
    requirement also satisfies any weaker valid alignment requirement.
6   The alignment requirement of a complete type can be queried using an _Alignof
    expression. The types char, signed char, and unsigned char shall have the
    weakest alignment requirement.
7   Comparing alignments is meaningful and provides the obvious results:
    -- Two alignments are equal when their numeric values are equal.
    -- Two alignments are different when their numeric values are not equal.
    -- When an alignment is larger than another it represents a stricter alignment.

6.3 [Conversions]


1   Several operators convert operand values from one type to another automatically. This
    subclause specifies the result required from such an implicit conversion, as well as those
    that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
    the conversions performed by most ordinary operators; it is supplemented as required by
    the discussion of each operator in 6.5.
2   Conversion of an operand value to a compatible type causes no change to the value or the
    representation.
    Forward references: cast operators (6.5.4).

6.3.1 [Arithmetic operands]

 Arithmetic operands

6.3.1.1 [Boolean, characters, and integers]


1   Every integer type has an integer conversion rank defined as follows:
    -- No two signed integer types shall have the same rank, even if they have the same
       representation.
    -- The rank of a signed integer type shall be greater than the rank of any signed integer
       type with less precision.
    -- The rank of long long int shall be greater than the rank of long int, which
       shall be greater than the rank of int, which shall be greater than the rank of short
       int, which shall be greater than the rank of signed char.
    -- The rank of any unsigned integer type shall equal the rank of the corresponding
       signed integer type, if any.
    -- The rank of any standard integer type shall be greater than the rank of any extended
       integer type with the same width.
    -- The rank of char shall equal the rank of signed char and unsigned char.
    -- The rank of _Bool shall be less than the rank of all other standard integer types.
    -- The rank of any enumerated type shall equal the rank of the compatible integer type
       (see 6.7.2.2).
    -- The rank of any extended signed integer type relative to another extended signed
       integer type with the same precision is implementation-defined, but still subject to the
       other rules for determining the integer conversion rank.
    -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
       greater rank than T3, then T1 has greater rank than T3.
2   The following may be used in an expression wherever an int or unsigned int may
    be used:

    -- An object or expression with an integer type (other than int or unsigned int)
       whose integer conversion rank is less than or equal to the rank of int and
       unsigned int.
    -- A bit-field of type _Bool, int, signed int, or unsigned int.
    If an int can represent all values of the original type (as restricted by the width, for a
    bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
    int. These are called the integer promotions.58) All other types are unchanged by the
    integer promotions.
Footnote 58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
        argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
        shift operators, as specified by their respective subclauses.
3   The integer promotions preserve value including sign. As discussed earlier, whether a
    ``plain'' char is treated as signed is implementation-defined.
    Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
    (6.7.2.1).

6.3.1.2 [Boolean type]


1   When any scalar value is converted to _Bool, the result is 0 if the value compares equal
    to 0; otherwise, the result is 1.59)
Footnote 59) NaNs do not compare equal to 0 and thus convert to 1.

6.3.1.3 [Signed and unsigned integers]


1   When a value with integer type is converted to another integer type other than _Bool, if
    the value can be represented by the new type, it is unchanged.
2   Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
    subtracting one more than the maximum value that can be represented in the new type
    until the value is in the range of the new type.60)
Footnote 60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
3   Otherwise, the new type is signed and the value cannot be represented in it; either the
    result is implementation-defined or an implementation-defined signal is raised.

6.3.1.4 [Real floating and integer]


1   When a finite value of real floating type is converted to an integer type other than _Bool,
    the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
    the integral part cannot be represented by the integer type, the behavior is undefined.61)

Footnote 61) The remaindering operation performed when a value of integer type is converted to unsigned type
        need not be performed when a value of real floating type is converted to unsigned type. Thus, the
        range of portable real floating values is (-1, Utype_MAX+1).
2   When a value of integer type is converted to a real floating type, if the value being
    converted can be represented exactly in the new type, it is unchanged. If the value being
    converted is in the range of values that can be represented but cannot be represented
    exactly, the result is either the nearest higher or nearest lower representable value, chosen
    in an implementation-defined manner. If the value being converted is outside the range of
    values that can be represented, the behavior is undefined. Results of some implicit
    conversions may be represented in greater range and precision than that required by the
    new type (see 6.3.1.8 and 6.8.6.4).

6.3.1.5 [Real floating types]


1   When a value of real floating type is converted to a real floating type, if the value being
    converted can be represented exactly in the new type, it is unchanged. If the value being
    converted is in the range of values that can be represented but cannot be represented
    exactly, the result is either the nearest higher or nearest lower representable value, chosen
    in an implementation-defined manner. If the value being converted is outside the range of
    values that can be represented, the behavior is undefined. Results of some implicit
    conversions may be represented in greater range and precision than that required by the
    new type (see 6.3.1.8 and 6.8.6.4).

6.3.1.6 [Complex types]


1   When a value of complex type is converted to another complex type, both the real and
    imaginary parts follow the conversion rules for the corresponding real types.

6.3.1.7 [Real and complex]


1   When a value of real type is converted to a complex type, the real part of the complex
    result value is determined by the rules of conversion to the corresponding real type and
    the imaginary part of the complex result value is a positive zero or an unsigned zero.
2   When a value of complex type is converted to a real type, the imaginary part of the
    complex value is discarded and the value of the real part is converted according to the
    conversion rules for the corresponding real type.

6.3.1.8 [Usual arithmetic conversions]


1   Many operators that expect operands of arithmetic type cause conversions and yield result
    types in a similar way. The purpose is to determine a common real type for the operands
    and result. For the specified operands, each operand is converted, without change of type
    domain, to a type whose corresponding real type is the common real type. Unless
    explicitly stated otherwise, the common real type is also the corresponding real type of
    the result, whose type domain is the type domain of the operands if they are the same,
    and complex otherwise. This pattern is called the usual arithmetic conversions:
          First, if the corresponding real type of either operand is long double, the other
          operand is converted, without change of type domain, to a type whose

           corresponding real type is long double.
           Otherwise, if the corresponding real type of either operand is double, the other
           operand is converted, without change of type domain, to a type whose
           corresponding real type is double.
           Otherwise, if the corresponding real type of either operand is float, the other
           operand is converted, without change of type domain, to a type whose
           corresponding real type is float.62)
           Otherwise, the integer promotions are performed on both operands. Then the
           following rules are applied to the promoted operands:
                  If both operands have the same type, then no further conversion is needed.
                  Otherwise, if both operands have signed integer types or both have unsigned
                  integer types, the operand with the type of lesser integer conversion rank is
                  converted to the type of the operand with greater rank.
                  Otherwise, if the operand that has unsigned integer type has rank greater or
                  equal to the rank of the type of the other operand, then the operand with
                  signed integer type is converted to the type of the operand with unsigned
                  integer type.
                  Otherwise, if the type of the operand with signed integer type can represent
                  all of the values of the type of the operand with unsigned integer type, then
                  the operand with unsigned integer type is converted to the type of the
                  operand with signed integer type.
                  Otherwise, both operands are converted to the unsigned integer type
                  corresponding to the type of the operand with signed integer type.
Footnote 62) For example, addition of a double _Complex and a float entails just the conversion of the
        float operand to double (and yields a double _Complex result).
2   The values of floating operands and of the results of floating expressions may be
    represented in greater range and precision than that required by the type; the types are not
    changed thereby.63)

Footnote 63) The cast and assignment operators are still required to remove extra range and precision.

6.3.2 [Other operands]

 Other operands

6.3.2.1 [Lvalues, arrays, and function designators]


1   An lvalue is an expression (with an object type other than void) that potentially
    designates an object;64) if an lvalue does not designate an object when it is evaluated, the
    behavior is undefined. When an object is said to have a particular type, the type is
    specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
    does not have array type, does not have an incomplete type, does not have a const-
    qualified type, and if it is a structure or union, does not have any member (including,
    recursively, any member or element of all contained aggregates or unions) with a const-
    qualified type.
Footnote 64) The name ``lvalue'' comes originally from the assignment expression E1 = E2, in which the left
        operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
        object ``locator value''. What is sometimes called ``rvalue'' is in this International Standard described
        as the ``value of an expression''.
         An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
         expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
2   Except when it is the operand of the sizeof operator, the _Alignof operator, the
    unary & operator, the ++ operator, the -- operator, or the left operand of the . operator
    or an assignment operator, an lvalue that does not have array type is converted to the
    value stored in the designated object (and is no longer an lvalue); this is called lvalue
    conversion. If the lvalue has qualified type, the value has the unqualified version of the
    type of the lvalue; additionally, if the lvalue has atomic type, the value has the non-atomic
    version of the type of the lvalue; otherwise, the value has the type of the lvalue. If the
    lvalue has an incomplete type and does not have array type, the behavior is undefined. If
    the lvalue designates an object of automatic storage duration that could have been
    declared with the register storage class (never had its address taken), and that object
    is uninitialized (not declared with an initializer and no assignment to it has been
    performed prior to use), the behavior is undefined.
3   Except when it is the operand of the sizeof operator, the _Alignof operator, or the
    unary & operator, or is a string literal used to initialize an array, an expression that has
    type ``array of type'' is converted to an expression with type ``pointer to type'' that points
    to the initial element of the array object and is not an lvalue. If the array object has
    register storage class, the behavior is undefined.
4   A function designator is an expression that has function type. Except when it is the
    operand of the sizeof operator, the _Alignof operator,65) or the unary & operator, a
    function designator with type ``function returning type'' is converted to an expression that

    has type ``pointer to function returning type''.
    Forward references: address and indirection operators (6.5.3.2), assignment operators
    (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix
    increment and decrement operators (6.5.2.4), prefix increment and decrement operators
    (6.5.3.1), the sizeof and _Alignof operators (6.5.3.4), structure and union members
    (6.5.2.3).
Footnote 65) Because this conversion does not occur, the operand of the sizeof or _Alignof operator remains
        a function designator and violates the constraints in 6.5.3.4.

6.3.2.2 [void]


1   The (nonexistent) value of a void expression (an expression that has type void) shall not
    be used in any way, and implicit or explicit conversions (except to void) shall not be
    applied to such an expression. If an expression of any other type is evaluated as a void
    expression, its value or designator is discarded. (A void expression is evaluated for its
    side effects.)

6.3.2.3 [Pointers]


1   A pointer to void may be converted to or from a pointer to any object type. A pointer to
    any object type may be converted to a pointer to void and back again; the result shall
    compare equal to the original pointer.
2   For any qualifier q , a pointer to a non-q -qualified type may be converted to a pointer to
    the q -qualified version of the type; the values stored in the original and converted pointers
    shall compare equal.
3   An integer constant expression with the value 0, or such an expression cast to type
    void *, is called a null pointer constant .66) If a null pointer constant is converted to a
    pointer type, the resulting pointer, called a null pointer , is guaranteed to compare unequal
    to a pointer to any object or function.
Footnote 66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19.
4   Conversion of a null pointer to another pointer type yields a null pointer of that type.
    Any two null pointers shall compare equal.
5   An integer may be converted to any pointer type. Except as previously specified, the
    result is implementation-defined, might not be correctly aligned, might not point to an
    entity of the referenced type, and might be a trap representation.67)
Footnote 67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to
        be consistent with the addressing structure of the execution environment.
6   Any pointer type may be converted to an integer type. Except as previously specified, the
    result is implementation-defined. If the result cannot be represented in the integer type,
    the behavior is undefined. The result need not be in the range of values of any integer
    type.

7   A pointer to an object type may be converted to a pointer to a different object type. If the
    resulting pointer is not correctly aligned68) for the referenced type, the behavior is
    undefined. Otherwise, when converted back again, the result shall compare equal to the
    original pointer. When a pointer to an object is converted to a pointer to a character type,
    the result points to the lowest addressed byte of the object. Successive increments of the
    result, up to the size of the object, yield pointers to the remaining bytes of the object.
Footnote 68) In general, the concept ``correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a
        pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
        correctly aligned for a pointer to type C.
8   A pointer to a function of one type may be converted to a pointer to a function of another
    type and back again; the result shall compare equal to the original pointer. If a converted
    pointer is used to call a function whose type is not compatible with the referenced type,
    the behavior is undefined.
    Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
    capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).


6.4 [Lexical elements]


1            token:
                      keyword
                      identifier
                      constant
                      string-literal
                      punctuator
             preprocessing-token:
                    header-name
                    identifier
                    pp-number
                    character-constant
                    string-literal
                    punctuator
                    each non-white-space character that cannot be one of the above
    Constraints
2   Each preprocessing token that is converted to a token shall have the lexical form of a
    keyword, an identifier, a constant, a string literal, or a punctuator.
    Semantics
3   A token is the minimal lexical element of the language in translation phases 7 and 8. The
    categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
    A preprocessing token is the minimal lexical element of the language in translation
    phases 3 through 6. The categories of preprocessing tokens are: header names,
    identifiers, preprocessing numbers, character constants, string literals, punctuators, and
    single non-white-space characters that do not lexically match the other preprocessing
    token categories.69) If a ' or a " character matches the last category, the behavior is
    undefined. Preprocessing tokens can be separated by white space; this consists of
    comments (described later), or white-space characters (space, horizontal tab, new-line,
    vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
    during translation phase 4, white space (or the absence thereof) serves as more than
    preprocessing token separation. White space may appear within a preprocessing token
    only as part of a header name or between the quotation characters in a character constant
    or string literal.

Footnote 69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
        occur in source files.
4   If the input stream has been parsed into preprocessing tokens up to a given character, the
    next preprocessing token is the longest sequence of characters that could constitute a
    preprocessing token. There is one exception to this rule: header name preprocessing
    tokens are recognized only within #include preprocessing directives and in
    implementation-defined locations within #pragma directives. In such contexts, a
    sequence of characters that could be either a header name or a string literal is recognized
    as the former.
5   EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
    valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
    might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
    fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
    not E is a macro name.

6   EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
    increment operators, even though the parse x ++ + ++ y might yield a correct expression.

    Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
    floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
    increment and decrement operators (6.5.2.4), prefix increment and decrement operators
    (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
    (6.4.5).

6.4.1 [Keywords]


1            keyword: one of
                   auto                          if                              unsigned
                   break                         inline                          void
                   case                          int                             volatile
                   char                          long                            while
                   const                         register                        _Alignas
                   continue                      restrict                        _Alignof
                   default                       return                          _Atomic
                   do                            short                           _Bool
                   double                        signed                          _Complex
                   else                          sizeof                          _Generic
                   enum                          static                          _Imaginary
                   extern                        struct                          _Noreturn
                   float                         switch                          _Static_assert
                   for                           typedef                         _Thread_local
                   goto                          union
    Semantics
2   The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
    keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for
    specifying imaginary types.70)
Footnote 70) One possible specification for imaginary types appears in annex G.

6.4.2 [Identifiers]

 Identifiers

6.4.2.1 [General]


1            identifier:
                     identifier-nondigit
                     identifier identifier-nondigit
                     identifier digit
             identifier-nondigit:
                     nondigit
                     universal-character-name
                     other implementation-defined characters
             nondigit: one of
                    _ a b            c    d    e    f     g    h    i    j     k    l    m
                        n o          p    q    r    s     t    u    v    w     x    y    z
                        A B          C    D    E    F     G    H    I    J     K    L    M
                        N O          P    Q    R    S     T    U    V    W     X    Y    Z
             digit: one of
                    0 1        2     3    4    5    6     7    8    9
    Semantics
2   An identifier is a sequence of nondigit characters (including the underscore _, the
    lowercase and uppercase Latin letters, and other characters) and digits, which designates
    one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
    There is no specific limit on the maximum length of an identifier.
3   Each universal character name in an identifier shall designate a character whose encoding
    in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character
    shall not be a universal character name designating a character whose encoding falls into
    one of the ranges specified in D.2. An implementation may allow multibyte characters
    that are not part of the basic source character set to appear in identifiers; which characters
    and their correspondence to universal character names is implementation-defined.

Footnote 71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
        name may be used in forming valid external identifiers. For example, some otherwise unused
        character or sequence of characters may be used to encode the \u in a universal character name.
        Extended characters may produce a long external identifier.
4   When preprocessing tokens are converted to tokens during translation phase 7, if a
    preprocessing token could be converted to either a keyword or an identifier, it is converted
    to a keyword.
    Implementation limits
5   As discussed in 5.2.4.1, an implementation may limit the number of significant initial
    characters in an identifier; the limit for an external name (an identifier that has external
    linkage) may be more restrictive than that for an internal name (a macro name or an
    identifier that does not have external linkage). The number of significant characters in an
    identifier is implementation-defined.
6   Any identifiers that differ in a significant character are different identifiers. If two
    identifiers differ only in nonsignificant characters, the behavior is undefined.
    Forward references: universal character names (6.4.3), macro replacement (6.10.3).

6.4.2.2 [Predefined identifiers]


1   The identifier _ _func_ _ shall be implicitly declared by the translator as if,
    immediately following the opening brace of each function definition, the declaration
             static const char _ _func_ _[] = "function-name";
    appeared, where function-name is the name of the lexically-enclosing function.72)
Footnote 72) Since the name _ _func_ _ is reserved for any use by the implementation (7.1.3), if any other
        identifier is explicitly declared using the name _ _func_ _, the behavior is undefined.
2   This name is encoded as if the implicit declaration had been written in the source
    character set and then translated into the execution character set as indicated in translation
    phase 5.
3   EXAMPLE        Consider the code fragment:
             #include <stdio.h>
             void myfunc(void)
             {
                   printf("%s\n", _ _func_ _);
                   /* ... */
             }
    Each time the function is called, it will print to the standard output stream:
             myfunc

    Forward references: function definitions (6.9.1).


6.4.3 [Universal character names]


1            universal-character-name:
                    \u hex-quad
                    \U hex-quad hex-quad
             hex-quad:
                    hexadecimal-digit hexadecimal-digit
                                 hexadecimal-digit hexadecimal-digit
    Constraints
2   A universal character name shall not specify a character whose short identifier is less than
    00A0 other than 0024 ($), 0040 (@), or 0060 (`), nor one in the range D800 through
    DFFF inclusive.73)
    Description
Footnote 73) The disallowed characters are the characters in the basic character set and the code positions reserved
        by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
        UTF-16).
3   Universal character names may be used in identifiers, character constants, and string
    literals to designate characters that are not in the basic character set.
    Semantics
4   The universal character name \Unnnnnnnn designates the character whose eight-digit
    short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal
    character name \unnnn designates the character whose four-digit short identifier is nnnn
    (and whose eight-digit short identifier is 0000 nnnn).

Footnote 74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997.

6.4.4 [Constants]


1            constant:
                    integer-constant
                    floating-constant
                    enumeration-constant
                    character-constant
    Constraints
2   Each constant shall have a type and the value of a constant shall be in the range of
    representable values for its type.
    Semantics
3   Each constant has a type, determined by its form and value, as detailed later.

6.4.4.1 [Integer constants]


1            integer-constant:
                     decimal-constant integer-suffixopt
                     octal-constant integer-suffixopt
                     hexadecimal-constant integer-suffixopt
             decimal-constant:
                   nonzero-digit
                   decimal-constant digit
             octal-constant:
                    0
                    octal-constant octal-digit
             hexadecimal-constant:
                   hexadecimal-prefix hexadecimal-digit
                   hexadecimal-constant hexadecimal-digit
             hexadecimal-prefix: one of
                   0x 0X
             nonzero-digit: one of
                    1 2 3 4           5    6     7   8    9
             octal-digit: one of
                     0 1 2 3          4    5     6   7
            hexadecimal-digit:    one of
                  0 1 2            3 4     5    6   7     8   9
                  a b c            d e     f
                  A B C            D E     F
            integer-suffix:
                    unsigned-suffix long-suffixopt
                    unsigned-suffix long-long-suffix
                    long-suffix unsigned-suffixopt
                    long-long-suffix unsigned-suffixopt
            unsigned-suffix: one of
                   u U
            long-suffix: one of
                   l L
            long-long-suffix: one of
                   ll LL
    Description
2   An integer constant begins with a digit, but has no period or exponent part. It may have a
    prefix that specifies its base and a suffix that specifies its type.
3   A decimal constant begins with a nonzero digit and consists of a sequence of decimal
    digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
    digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
    by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
    10 through 15 respectively.
    Semantics
4   The value of a decimal constant is computed base 10; that of an octal constant, base 8;
    that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
5   The type of an integer constant is the first of the corresponding list in which its value can
    be represented.
                                                                     Octal or Hexadecimal
    Suffix                      Decimal Constant                           Constant

    none                int                                    int
                        long int                               unsigned int
                        long long int                          long int
                                                               unsigned long int
                                                               long long int
                                                               unsigned long long int

    u or U              unsigned int                           unsigned int
                        unsigned long int                      unsigned long int
                        unsigned long long int                 unsigned long long int

    l or L              long int                               long int
                        long long int                          unsigned long int
                                                               long long int
                                                               unsigned long long int

    Both u or U         unsigned long int                      unsigned long int
    and l or L          unsigned long long int                 unsigned long long int

    ll or LL            long long int                          long long int
                                                               unsigned long long int

    Both u or U         unsigned long long int                 unsigned long long int
    and ll or LL
6   If an integer constant cannot be represented by any type in its list, it may have an
    extended integer type, if the extended integer type can represent its value. If all of the
    types in the list for the constant are signed, the extended integer type shall be signed. If
    all of the types in the list for the constant are unsigned, the extended integer type shall be
    unsigned. If the list contains both signed and unsigned types, the extended integer type
    may be signed or unsigned. If an integer constant cannot be represented by any type in
    its list and has no extended integer type, then the integer constant has no type.

6.4.4.2 [Floating constants]


1            floating-constant:
                     decimal-floating-constant
                     hexadecimal-floating-constant
             decimal-floating-constant:
                   fractional-constant exponent-partopt floating-suffixopt
                   digit-sequence exponent-part floating-suffixopt
             hexadecimal-floating-constant:
                   hexadecimal-prefix hexadecimal-fractional-constant
                                   binary-exponent-part floating-suffixopt
                   hexadecimal-prefix hexadecimal-digit-sequence
                                   binary-exponent-part floating-suffixopt
             fractional-constant:
                     digit-sequenceopt . digit-sequence
                     digit-sequence .
             exponent-part:
                   e signopt digit-sequence
                   E signopt digit-sequence
             sign: one of
                    + -
             digit-sequence:
                     digit
                     digit-sequence digit
             hexadecimal-fractional-constant:
                   hexadecimal-digit-sequenceopt .
                                  hexadecimal-digit-sequence
                   hexadecimal-digit-sequence .
             binary-exponent-part:
                    p signopt digit-sequence
                    P signopt digit-sequence
             hexadecimal-digit-sequence:
                   hexadecimal-digit
                   hexadecimal-digit-sequence hexadecimal-digit
             floating-suffix: one of
                     f l F L

    Description
2   A floating constant has a significand part that may be followed by an exponent part and a
    suffix that specifies its type. The components of the significand part may include a digit
    sequence representing the whole-number part, followed by a period (.), followed by a
    digit sequence representing the fraction part. The components of the exponent part are an
    e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
    Either the whole-number part or the fraction part has to be present; for decimal floating
    constants, either the period or the exponent part has to be present.
    Semantics
3   The significand part is interpreted as a (decimal or hexadecimal) rational number; the
    digit sequence in the exponent part is interpreted as a decimal integer. For decimal
    floating constants, the exponent indicates the power of 10 by which the significand part is
    to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
    by which the significand part is to be scaled. For decimal floating constants, and also for
    hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
    the nearest representable value, or the larger or smaller representable value immediately
    adjacent to the nearest representable value, chosen in an implementation-defined manner.
    For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
    correctly rounded.
4   An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
    type float. If suffixed by the letter l or L, it has type long double.
5   Floating constants are converted to internal format as if at translation-time. The
    conversion of a floating constant shall not raise an exceptional condition or a floating-
    point exception at execution time. All floating constants of the same source form75) shall
    convert to the same internal format with the same value.
    Recommended practice
Footnote 75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not
        convert to the same internal format and value.
6   The implementation should produce a diagnostic message if a hexadecimal constant
    cannot be represented exactly in its evaluation format; the implementation should then
    proceed with the translation of the program.
7   The translation-time conversion of floating constants should match the execution-time
    conversion of character strings by library functions, such as strtod, given matching
    inputs suitable for both conversions, the same result format, and default execution-time
    rounding.76)

Footnote 76) The specification for the library functions recommends more accurate conversion than required for
        floating constants (see 7.22.1.3).

6.4.4.3 [Enumeration constants]


1            enumeration-constant:
                   identifier
    Semantics
2   An identifier declared as an enumeration constant has type int.
    Forward references: enumeration specifiers (6.7.2.2).

6.4.4.4 [Character constants]


1            character-constant:
                    ' c-char-sequence '
                    L' c-char-sequence '
                    u' c-char-sequence '
                    U' c-char-sequence '
             c-char-sequence:
                    c-char
                    c-char-sequence c-char
             c-char:
                       any member of the source character set except
                                    the single-quote ', backslash \, or new-line character
                       escape-sequence
             escape-sequence:
                    simple-escape-sequence
                    octal-escape-sequence
                    hexadecimal-escape-sequence
                    universal-character-name
             simple-escape-sequence: one of
                    \' \" \? \\
                    \a \b \f \n \r                  \t    \v
             octal-escape-sequence:
                     \ octal-digit
                     \ octal-digit octal-digit
                     \ octal-digit octal-digit octal-digit
           hexadecimal-escape-sequence:
                 \x hexadecimal-digit
                 hexadecimal-escape-sequence hexadecimal-digit
    Description
2   An integer character constant is a sequence of one or more multibyte characters enclosed
    in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
    letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
    any members of the source character set; they are mapped in an implementation-defined
    manner to members of the execution character set.
3   The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
    arbitrary integer values are representable according to the following table of escape
    sequences:
          single quote '            \'
          double quote "            \"
          question mark ?           \?
          backslash \               \\
          octal character           \octal digits
          hexadecimal character     \x hexadecimal digits
4   The double-quote " and question-mark ? are representable either by themselves or by the
    escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
    shall be represented, respectively, by the escape sequences \' and \\.
5   The octal digits that follow the backslash in an octal escape sequence are taken to be part
    of the construction of a single character for an integer character constant or of a single
    wide character for a wide character constant. The numerical value of the octal integer so
    formed specifies the value of the desired character or wide character.
6   The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
    sequence are taken to be part of the construction of a single character for an integer
    character constant or of a single wide character for a wide character constant. The
    numerical value of the hexadecimal integer so formed specifies the value of the desired
    character or wide character.
7   Each octal or hexadecimal escape sequence is the longest sequence of characters that can
    constitute the escape sequence.
8   In addition, characters not in the basic character set are representable by universal
    character names and certain nongraphic characters are representable by escape sequences
    consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
    and \v.77)

     Constraints
Footnote 77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
         the result is not a token and a diagnostic is required. See ``future language directions'' (6.11.4).
9    The value of an octal or hexadecimal escape sequence shall be in the range of
     representable values for the corresponding type:
            Prefix     Corresponding Type
            none       unsigned char
            L          the unsigned type corresponding to wchar_t
            u          char16_t
            U          char32_t
     Semantics
10   An integer character constant has type int. The value of an integer character constant
     containing a single character that maps to a single-byte execution character is the
     numerical value of the representation of the mapped character interpreted as an integer.
     The value of an integer character constant containing more than one character (e.g.,
     'ab'), or containing a character or escape sequence that does not map to a single-byte
     execution character, is implementation-defined. If an integer character constant contains
     a single character or escape sequence, its value is the one that results when an object with
     type char whose value is that of the single character or escape sequence is converted to
     type int.
11   A wide character constant prefixed by the letter L has type wchar_t, an integer type
     defined in the <stddef.h> header; a wide character constant prefixed by the letter u or
     U has type char16_t or char32_t, respectively, unsigned integer types defined in the
     <uchar.h> header. The value of a wide character constant containing a single
     multibyte character that maps to a single member of the extended execution character set
     is the wide character corresponding to that multibyte character, as defined by the
     mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an
     implementation-defined current locale. The value of a wide character constant containing
     more than one multibyte character or a single multibyte character that maps to multiple
     members of the extended execution character set, or containing a multibyte character or
     escape sequence not represented in the extended execution character set, is
     implementation-defined.
12   EXAMPLE 1       The construction '\0' is commonly used to represent the null character.

13   EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight
     bits for objects that have type char. In an implementation in which type char has the same range of
     values as signed char, the integer character constant '\xFF' has the value -1; if type char has the
     same range of values as unsigned char, the character constant '\xFF' has the value +255.

14   EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
     specifies an integer character constant containing only one character, since a hexadecimal escape sequence
     is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
     two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
     escape sequence is terminated after three octal digits. (The value of this two-character integer character
     constant is implementation-defined.)

15   EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
     L'\1234' specifies the implementation-defined value that results from the combination of the values
     0123 and '4'.

     Forward references: common definitions <stddef.h> (7.19), the mbtowc function
     (7.22.7.2), Unicode utilities <uchar.h> (7.28).

6.4.5 [String literals]


1             string-literal:
                      encoding-prefixopt " s-char-sequenceopt "
              encoding-prefix:
                     u8
                     u
                     U
                     L
              s-char-sequence:
                     s-char
                     s-char-sequence s-char
              s-char:
                        any member of the source character set except
                                     the double-quote ", backslash \, or new-line character
                        escape-sequence
     Constraints
2    A sequence of adjacent string literal tokens shall not include both a wide string literal and
     a UTF-8 string literal.
     Description
3    A character string literal is a sequence of zero or more multibyte characters enclosed in
     double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8.
     A wide string literal is the same, except prefixed by the letter L, u, or U.
4    The same considerations apply to each element of the sequence in a string literal as if it
     were in an integer character constant (for a character or UTF-8 string literal) or a wide
     character constant (for a wide string literal), except that the single-quote ' is
     representable either by itself or by the escape sequence \', but the double-quote " shall
    be represented by the escape sequence \".
    Semantics
5   In translation phase 6, the multibyte character sequences specified by any sequence of
    adjacent character and identically-prefixed string literal tokens are concatenated into a
    single multibyte character sequence. If any of the tokens has an encoding prefix, the
    resulting multibyte character sequence is treated as having the same prefix; otherwise, it
    is treated as a character string literal. Whether differently-prefixed wide string literal
    tokens can be concatenated and, if so, the treatment of the resulting multibyte character
    sequence are implementation-defined.
6   In translation phase 7, a byte or code of value zero is appended to each multibyte
    character sequence that results from a string literal or literals.78) The multibyte character
    sequence is then used to initialize an array of static storage duration and length just
    sufficient to contain the sequence. For character string literals, the array elements have
    type char, and are initialized with the individual bytes of the multibyte character
    sequence. For UTF-8 string literals, the array elements have type char, and are
    initialized with the characters of the multibyte character sequence, as encoded in UTF-8.
    For wide string literals prefixed by the letter L, the array elements have type wchar_t
    and are initialized with the sequence of wide characters corresponding to the multibyte
    character sequence, as defined by the mbstowcs function with an implementation-
    defined current locale. For wide string literals prefixed by the letter u or U, the array
    elements have type char16_t or char32_t, respectively, and are initialized with the
    sequence of wide characters corresponding to the multibyte character sequence, as
    defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
    its type, with an implementation-defined current locale. The value of a string literal
    containing a multibyte character or escape sequence not represented in the execution
    character set is implementation-defined.
Footnote 78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
        \0 escape sequence.
7   It is unspecified whether these arrays are distinct provided their elements have the
    appropriate values. If the program attempts to modify such an array, the behavior is
    undefined.
8   EXAMPLE 1      This pair of adjacent character string literals
             "\x12" "3"
    produces a single character string literal containing the two characters whose values are '\x12' and '3',
    because escape sequences are converted into single members of the execution character set just prior to
    adjacent string literal concatenation.

9   EXAMPLE 2      Each of the sequences of adjacent string literal tokens

             "a" "b" L"c"
             "a" L"b" "c"
             L"a" "b" L"c"
             L"a" L"b" L"c"
    is equivalent to the string literal
             L"abc"
    Likewise, each of the sequences
             "a" "b" u"c"
             "a" u"b" "c"
             u"a" "b" u"c"
             u"a" u"b" u"c"
    is equivalent to
             u"abc"

    Forward references: common definitions <stddef.h> (7.19), the mbstowcs
    function (7.22.8.1), Unicode utilities <uchar.h> (7.28).

6.4.6 [Punctuators]


1            punctuator: one of
                    [ ] ( ) { } . ->
                    ++ -- & * + - ~ !
                    / % << >> < > <= >=                              ==       !=    ^    |   &&   ||
                    ? : ; ...
                    = *= /= %= += -= <<=                             >>=       &=       ^=   |=
                    , # ##
                    <: :> <% %> %: %:%:
    Semantics
2   A punctuator is a symbol that has independent syntactic and semantic significance.
    Depending on context, it may specify an operation to be performed (which in turn may
    yield a value or a function designator, produce a side effect, or some combination thereof)
    in which case it is known as an operator (other forms of operator also exist in some
    contexts). An operand is an entity on which an operator acts.
3   In all aspects of the language, the six tokens79)
             <:    :>      <%    %>     %:     %:%:
    behave, respectively, the same as the six tokens
             [     ]       {     }      #      ##
    except for their spelling.80)
    Forward references: expressions (6.5), declarations (6.7), preprocessing directives
    (6.10), statements (6.8).
Footnote 79) These tokens are sometimes called ``digraphs''.
Footnote 80) Thus [ and <: behave differently when ``stringized'' (see 6.10.3.2), but can otherwise be freely
        interchanged.

6.4.7 [Header names]


1            header-name:
                    < h-char-sequence >
                    " q-char-sequence "
             h-char-sequence:
                    h-char
                    h-char-sequence h-char
             h-char:
                       any member of the source character set except
                                    the new-line character and >
             q-char-sequence:
                    q-char
                    q-char-sequence q-char
             q-char:
                       any member of the source character set except
                                    the new-line character and "
    Semantics
2   The sequences in both forms of header names are mapped in an implementation-defined
    manner to headers or external source file names as specified in 6.10.2.
3   If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
    the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the

    sequence between the " delimiters, the behavior is undefined.81) Header name
    preprocessing tokens are recognized only within #include preprocessing directives and
    in implementation-defined locations within #pragma directives.82)
Footnote 81) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
Footnote 82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.
4   EXAMPLE       The following sequence of characters:
             0x3<1/a.h>1e2
             #include <1/a.h>
             #define const.member@$
    forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
    by a { on the left and a } on the right).
             {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
             {#}{include} {<1/a.h>}
             {#}{define} {const}{.}{member}{@}{$}

    Forward references: source file inclusion (6.10.2).

6.4.8 [Preprocessing numbers]


1            pp-number:
                   digit
                   . digit
                   pp-number       digit
                   pp-number       identifier-nondigit
                   pp-number       e sign
                   pp-number       E sign
                   pp-number       p sign
                   pp-number       P sign
                   pp-number       .
    Description
2   A preprocessing number begins with a digit optionally preceded by a period (.) and may
    be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
    p+, p-, P+, or P-.
3   Preprocessing number tokens lexically include all floating and integer constant tokens.
    Semantics
4   A preprocessing number does not have type or a value; it acquires both after a successful
    conversion (as part of translation phase 7) to a floating constant token or an integer
    constant token.


6.4.9 [Comments]


1   Except within a character constant, a string literal, or a comment, the characters /*
    introduce a comment. The contents of such a comment are examined only to identify
    multibyte characters and to find the characters */ that terminate it.83)
Footnote 83) Thus, /* ... */ comments do not nest.
2   Except within a character constant, a string literal, or a comment, the characters //
    introduce a comment that includes all multibyte characters up to, but not including, the
    next new-line character. The contents of such a comment are examined only to identify
    multibyte characters and to find the terminating new-line character.
3   EXAMPLE
             "a//b"                             //   four-character string literal
             #include "//e"                     //   undefined behavior
             // */                              //   comment, not syntax error
             f = g/**//h;                       //   equivalent to f = g / h;
             //\
             i();                               // part of a two-line comment
             /\
             / j();                             // part of a two-line comment
             #define glue(x,y) x##y
             glue(/,/) k();                     // syntax error, not comment
             /*//*/ l();                        // equivalent to l();
             m = n//**/o
                + p;                            // equivalent to m = n + p;


6.5 [Expressions]


1   An expression is a sequence of operators and operands that specifies computation of a
    value, or that designates an object or a function, or that generates side effects, or that
    performs a combination thereof. The value computations of the operands of an operator
    are sequenced before the value computation of the result of the operator.
2   If a side effect on a scalar object is unsequenced relative to either a different side effect
    on the same scalar object or a value computation using the value of the same scalar
    object, the behavior is undefined. If there are multiple allowable orderings of the
    subexpressions of an expression, the behavior is undefined if such an unsequenced side
    effect occurs in any of the orderings.84)
Footnote 84) This paragraph renders undefined statement expressions such as
                  i = ++i + 1;
                  a[i++] = i;
         while allowing
                  i = i + 1;
                  a[i] = i;
3   The grouping of operators and operands is indicated by the syntax.85) Except as specified
    later, side effects and value computations of subexpressions are unsequenced.86)
Footnote 85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
        as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
        expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
        6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
        (6.5.3), and an operand contained between any of the following pairs of operators: grouping
        parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
        the conditional operator ? : (6.5.15).
         Within each major subclause, the operators have the same precedence. Left- or right-associativity is
         indicated in each subclause by the syntax for the expressions discussed therein.
Footnote 86) In an expression that is evaluated more than once during the execution of a program, unsequenced and
        indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
        different evaluations.
4   Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
    collectively described as bitwise operators) are required to have operands that have
    integer type. These operators yield values that depend on the internal representations of
    integers, and have implementation-defined and undefined aspects for signed types.
5   If an exceptional condition occurs during the evaluation of an expression (that is, if the
    result is not mathematically defined or not in the range of representable values for its
    type), the behavior is undefined.

6   The effective type of an object for an access to its stored value is the declared type of the
    object, if any.87) If a value is stored into an object having no declared type through an
    lvalue having a type that is not a character type, then the type of the lvalue becomes the
    effective type of the object for that access and for subsequent accesses that do not modify
    the stored value. If a value is copied into an object having no declared type using
    memcpy or memmove, or is copied as an array of character type, then the effective type
    of the modified object for that access and for subsequent accesses that do not modify the
    value is the effective type of the object from which the value is copied, if it has one. For
    all other accesses to an object having no declared type, the effective type of the object is
    simply the type of the lvalue used for the access.
Footnote 87) Allocated objects have no declared type.
7   An object shall have its stored value accessed only by an lvalue expression that has one of
    the following types:88)
    -- a type compatible with the effective type of the object,
    -- a qualified version of a type compatible with the effective type of the object,
    -- a type that is the signed or unsigned type corresponding to the effective type of the
       object,
    -- a type that is the signed or unsigned type corresponding to a qualified version of the
       effective type of the object,
    -- an aggregate or union type that includes one of the aforementioned types among its
       members (including, recursively, a member of a subaggregate or contained union), or
    -- a character type.
Footnote 88) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
8   A floating expression may be contracted , that is, evaluated as though it were a single
    operation, thereby omitting rounding errors implied by the source code and the
    expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a
    way to disallow contracted expressions. Otherwise, whether and how expressions are
    contracted is implementation-defined.90)
    Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.24.2).

Footnote 89) The intermediate operations in the contracted expression are evaluated as if to infinite range and
        precision, while the final operation is rounded to the format determined by the expression evaluation
        method. A contracted expression might also omit the raising of floating-point exceptions.
Footnote 90) This license is specifically intended to allow implementations to exploit fast machine instructions that
        combine multiple C operators. As contractions potentially undermine predictability, and can even
        decrease accuracy for containing expressions, their use needs to be well-defined and clearly
        documented.

6.5.1 [Primary expressions]


1            primary-expression:
                    identifier
                    constant
                    string-literal
                    ( expression )
                    generic-selection
    Semantics
2   An identifier is a primary expression, provided it has been declared as designating an
    object (in which case it is an lvalue) or a function (in which case it is a function
    designator).91)
Footnote 91) Thus, an undeclared identifier is a violation of the syntax.
3   A constant is a primary expression. Its type depends on its form and value, as detailed in 6.4.4.
4   A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
5   A parenthesized expression is a primary expression. Its type and value are identical to
    those of the unparenthesized expression. It is an lvalue, a function designator, or a void
    expression if the unparenthesized expression is, respectively, an lvalue, a function
    designator, or a void expression.
6   A generic selection is a primary expression. Its type and value depend on the selected
    generic association, as detailed in the following subclause.
    Forward references: declarations (6.7).

6.5.1.1 [Generic selection]


1            generic-selection:
                    _Generic ( assignment-expression , generic-assoc-list )
             generic-assoc-list:
                    generic-association
                    generic-assoc-list , generic-association
             generic-association:
                    type-name : assignment-expression
                    default : assignment-expression

    Constraints
2   A generic selection shall have no more than one default generic association. The type
    name in a generic association shall specify a complete object type other than a variably
    modified type. No two generic associations in the same generic selection shall specify
    compatible types. The controlling expression of a generic selection shall have type
    compatible with at most one of the types named in its generic association list. If a
    generic selection has no default generic association, its controlling expression shall
    have type compatible with exactly one of the types named in its generic association list.
    Semantics
3   The controlling expression of a generic selection is not evaluated. If a generic selection
    has a generic association with a type name that is compatible with the type of the
    controlling expression, then the result expression of the generic selection is the
    expression in that generic association. Otherwise, the result expression of the generic
    selection is the expression in the default generic association. None of the expressions
    from any other generic association of the generic selection is evaluated.
4   The type and value of a generic selection are identical to those of its result expression. It
    is an lvalue, a function designator, or a void expression if its result expression is,
    respectively, an lvalue, a function designator, or a void expression.
5   EXAMPLE      The cbrt type-generic macro could be implemented as follows:
             #define cbrt(X) _Generic((X),                                      \
                                     long double: cbrtl,                        \
                                     default: cbrt,                             \
                                     float: cbrtf                               \
                                     )(X)


6.5.2 [Postfix operators]


1            postfix-expression:
                     primary-expression
                     postfix-expression [ expression ]
                     postfix-expression ( argument-expression-listopt )
                     postfix-expression . identifier
                     postfix-expression -> identifier
                     postfix-expression ++
                     postfix-expression --
                     ( type-name ) { initializer-list }
                     ( type-name ) { initializer-list , }
             argument-expression-list:
                   assignment-expression
                   argument-expression-list , assignment-expression

6.5.2.1 [Array subscripting]


1   One of the expressions shall have type ``pointer to complete object type'', the other
    expression shall have integer type, and the result has type ``type''.
    Semantics
2   A postfix expression followed by an expression in square brackets [] is a subscripted
    designation of an element of an array object. The definition of the subscript operator []
    is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
    apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
    initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
    element of E1 (counting from zero).
3   Successive subscript operators designate an element of a multidimensional array object.
    If E is an n-dimensional array ( n  2) with dimensions i × j × . . . × k , then E (used as
    other than an lvalue) is converted to a pointer to an ( n - 1)-dimensional array with
    dimensions j × . . . × k . If the unary * operator is applied to this pointer explicitly, or
    implicitly as a result of subscripting, the result is the referenced ( n - 1)-dimensional
    array, which itself is converted into a pointer if used as other than an lvalue. It follows
    from this that arrays are stored in row-major order (last subscript varies fastest).
4   EXAMPLE        Consider the array object defined by the declaration
             int x[3][5];
    Here x is a 3 × 5 array of ints; more precisely, x is an array of three element objects, each of which is an
    array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
    a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
    entails multiplying i by the size of the object to which the pointer points, namely an array of five int
    objects. The results are added and indirection is applied to yield an array of five ints. When used in the
    expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
    yields an int.

    Forward references: additive operators (6.5.6), address and indirection operators
    (6.5.3.2), array declarators (6.7.6.2).

6.5.2.2 [Function calls]


1   The expression that denotes the called function92) shall have type pointer to function
    returning void or returning a complete object type other than an array type.
Footnote 92) Most often, this is the result of converting an identifier that is a function designator.
2   If the expression that denotes the called function has a type that includes a prototype, the
    number of arguments shall agree with the number of parameters. Each argument shall
    have a type such that its value may be assigned to an object with the unqualified version
    of the type of its corresponding parameter.
    Semantics
3   A postfix expression followed by parentheses () containing a possibly empty, comma-
    separated list of expressions is a function call. The postfix expression denotes the called
    function. The list of expressions specifies the arguments to the function.
4   An argument may be an expression of any complete object type. In preparing for the call
    to a function, the arguments are evaluated, and each parameter is assigned the value of the
    corresponding argument.93)
Footnote 93) A function may change the values of its parameters, but these changes cannot affect the values of the
        arguments. On the other hand, it is possible to pass a pointer to an object, and the function may
        change the value of the object pointed to. A parameter declared to have array or function type is
        adjusted to have a pointer type as described in 6.9.1.
5   If the expression that denotes the called function has type pointer to function returning an
    object type, the function call expression has the same type as that object type, and has the
    value determined as specified in 6.8.6.4. Otherwise, the function call has type void.
6   If the expression that denotes the called function has a type that does not include a
    prototype, the integer promotions are performed on each argument, and arguments that
    have type float are promoted to double. These are called the default argument
    promotions. If the number of arguments does not equal the number of parameters, the
    behavior is undefined. If the function is defined with a type that includes a prototype, and
    either the prototype ends with an ellipsis (, ...) or the types of the arguments after
    promotion are not compatible with the types of the parameters, the behavior is undefined.
    If the function is defined with a type that does not include a prototype, and the types of
    the arguments after promotion are not compatible with those of the parameters after
    promotion, the behavior is undefined, except for the following cases:
    -- one promoted type is a signed integer type, the other promoted type is the
       corresponding unsigned integer type, and the value is representable in both types;

     -- both types are pointers to qualified or unqualified versions of a character type or
        void.
7    If the expression that denotes the called function has a type that does include a prototype,
     the arguments are implicitly converted, as if by assignment, to the types of the
     corresponding parameters, taking the type of each parameter to be the unqualified version
     of its declared type. The ellipsis notation in a function prototype declarator causes
     argument type conversion to stop after the last declared parameter. The default argument
     promotions are performed on trailing arguments.
8    No other conversions are performed implicitly; in particular, the number and types of
     arguments are not compared with those of the parameters in a function definition that
     does not include a function prototype declarator.
9    If the function is defined with a type that is not compatible with the type (of the
     expression) pointed to by the expression that denotes the called function, the behavior is
     undefined.
10   There is a sequence point after the evaluations of the function designator and the actual
     arguments but before the actual call. Every evaluation in the calling function (including
     other function calls) that is not otherwise specifically sequenced before or after the
     execution of the body of the called function is indeterminately sequenced with respect to
     the execution of the called function.94)
Footnote 94) In other words, function executions do not ``interleave'' with each other.
11   Recursive function calls shall be permitted, both directly and indirectly through any chain
     of other functions.
12   EXAMPLE        In the function call
              (*pf[f1()]) (f2(), f3() + f4())
     the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
     the function pointed to by pf[f1()] is called.

     Forward references: function declarators (including prototypes) (6.7.6.3), function
     definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).

6.5.2.3 [Structure and union members]


1    The first operand of the . operator shall have an atomic, qualified, or unqualified
     structure or union type, and the second operand shall name a member of that type.
2    The first operand of the -> operator shall have type ``pointer to atomic, qualified, or
     unqualified structure'' or ``pointer to atomic, qualified, or unqualified union'', and the
     second operand shall name a member of the type pointed to.

    Semantics
3   A postfix expression followed by the . operator and an identifier designates a member of
    a structure or union object. The value is that of the named member,95) and is an lvalue if
    the first expression is an lvalue. If the first expression has qualified type, the result has
    the so-qualified version of the type of the designated member.
Footnote 95) If the member used to read the contents of a union object is not the same as the member last used to
        store a value in the object, the appropriate part of the object representation of the value is reinterpreted
        as an object representation in the new type as described in 6.2.6 (a process sometimes called ``type
        punning''). This might be a trap representation.
4   A postfix expression followed by the -> operator and an identifier designates a member
    of a structure or union object. The value is that of the named member of the object to
    which the first expression points, and is an lvalue.96) If the first expression is a pointer to
    a qualified type, the result has the so-qualified version of the type of the designated
    member.
Footnote 96) If &E is a valid pointer expression (where & is the ``address-of '' operator, which generates a pointer to
        its operand), the expression (&E)->MOS is the same as E.MOS.
5   Accessing a member of an atomic structure or union object results in undefined
    behavior.97)
Footnote 97) For example, a data race would occur if access to the entire structure or union in one thread conflicts
        with access to a member from another thread, where at least one access is a modification. Members
        can be safely accessed using a non-atomic object which is assigned to or from the atomic object.
6   One special guarantee is made in order to simplify the use of unions: if a union contains
    several structures that share a common initial sequence (see below), and if the union
    object currently contains one of these structures, it is permitted to inspect the common
    initial part of any of them anywhere that a declaration of the completed type of the union
    is visible. Two structures share a common initial sequence if corresponding members
    have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
    initial members.
7   EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
    union, f().x is a valid postfix expression but is not an lvalue.

8   EXAMPLE 2       In:
             struct s { int i; const int ci; };
             struct s s;
             const struct s cs;
             volatile struct s vs;
    the various members have the types:

             s.i        int
             s.ci       const int
             cs.i       const int
             cs.ci      const int
             vs.i       volatile int
             vs.ci      volatile const int

9   EXAMPLE 3       The following is a valid fragment:
             union {
                     struct {
                           int      alltypes;
                     } n;
                     struct {
                           int      type;
                           int      intnode;
                     } ni;
                     struct {
                           int      type;
                           double doublenode;
                     } nf;
             } u;
             u.nf.type = 1;
             u.nf.doublenode = 3.14;
             /* ... */
             if (u.n.alltypes == 1)
                     if (sin(u.nf.doublenode) == 0.0)
                           /* ... */
    The following is not a valid fragment (because the union type is not visible within function f):
             struct t1 { int m; };
             struct t2 { int m; };
             int f(struct t1 *p1, struct t2 *p2)
             {
                   if (p1->m < 0)
                           p2->m = -p2->m;
                   return p1->m;
             }
             int g()
             {
                   union {
                           struct t1 s1;
                           struct t2 s2;
                   } u;
                   /* ... */
                   return f(&u.s1, &u.s2);
             }

    Forward references: address and indirection operators (6.5.3.2), structure and union
    specifiers (6.7.2.1).


6.5.2.4 [Postfix increment and decrement operators]


1   The operand of the postfix increment or decrement operator shall have atomic, qualified,
    or unqualified real or pointer type, and shall be a modifiable lvalue.
    Semantics
2   The result of the postfix ++ operator is the value of the operand. As a side effect, the
    value of the operand object is incremented (that is, the value 1 of the appropriate type is
    added to it). See the discussions of additive operators and compound assignment for
    information on constraints, types, and conversions and the effects of operations on
    pointers. The value computation of the result is sequenced before the side effect of
    updating the stored value of the operand. With respect to an indeterminately-sequenced
    function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
    with atomic type is a read-modify-write operation with memory_order_seq_cst
    memory order semantics.98)
Footnote 98) Where a pointer to an atomic object can be formed and E has integer type, E++ is equivalent to the
        following code sequence where T is the type of E:
                  T *addr = &E;
                  T old = *addr;
                  T new;
                  do {
                         new = old + 1;
                  } while (!atomic_compare_exchange_strong(addr, &old, new));
         with old being the result of the operation.
         Special care must be taken if E has floating type; see 6.5.16.2.
3   The postfix -- operator is analogous to the postfix ++ operator, except that the value of
    the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
    it).
    Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

6.5.2.5 [Compound literals]


1   The type name shall specify a complete object type or an array of unknown size, but not a
    variable length array type.
2   All the constraints for initializer lists in 6.7.9 also apply to compound literals.
    Semantics
3   A postfix expression that consists of a parenthesized type name followed by a brace-
    enclosed list of initializers is a compound literal . It provides an unnamed object whose

     value is given by the initializer list.99)
Footnote 99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
         or void only, and the result of a cast expression is not an lvalue.
4    If the type name specifies an array of unknown size, the size is determined by the
     initializer list as specified in 6.7.9, and the type of the compound literal is that of the
     completed array type. Otherwise (when the type name specifies an object type), the type
     of the compound literal is that specified by the type name. In either case, the result is an
     lvalue.
5    The value of the compound literal is that of an unnamed object initialized by the
     initializer list. If the compound literal occurs outside the body of a function, the object
     has static storage duration; otherwise, it has automatic storage duration associated with
     the enclosing block.
6    All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100)
Footnote 100) For example, subobjects without explicit initializers are initialized to zero.
7    String literals, and compound literals with const-qualified types, need not designate
     distinct objects.101)
Footnote 101) This allows implementations to share storage for string literals and constant compound literals with
          the same or overlapping representations.
8    EXAMPLE 1       The file scope definition
              int *p = (int []){2, 4};
     initializes p to point to the first element of an array of two ints, the first having the value two and the
     second, four. The expressions in this compound literal are required to be constant. The unnamed object
     has static storage duration.

9    EXAMPLE 2       In contrast, in
              void f(void)
              {
                    int *p;
                    /*...*/
                    p = (int [2]){*p};
                    /*...*/
              }
     p is assigned the address of the first element of an array of two ints, the first having the value previously
     pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
     unnamed object has automatic storage duration.

10   EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
     created using compound literals can be passed to functions without depending on member order:
              drawline((struct point){.x=1, .y=1},
                    (struct point){.x=3, .y=4});

     Or, if drawline instead expected pointers to struct point:
              drawline(&(struct point){.x=1, .y=1},
                    &(struct point){.x=3, .y=4});

11   EXAMPLE 4        A read-only compound literal can be specified through constructions like:
              (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}

12   EXAMPLE 5        The following three expressions have different meanings:
              "/tmp/fileXXXXXX"
              (char []){"/tmp/fileXXXXXX"}
              (const char []){"/tmp/fileXXXXXX"}
     The first always has static storage duration and has type array of char, but need not be modifiable; the last
     two have automatic storage duration when they occur within the body of a function, and the first of these
     two is modifiable.

13   EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
     and can even be shared. For example,
              (const char []){"abc"} == "abc"
     might yield 1 if the literals' storage is shared.

14   EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
     linked object. For example, there is no way to write a self-referential compound literal that could be used
     as the function argument in place of the named object endless_zeros below:
              struct int_list { int car; struct int_list *cdr; };
              struct int_list endless_zeros = {0, &endless_zeros};
              eval(endless_zeros);

15   EXAMPLE 8        Each compound literal creates only a single object in a given scope:
              struct s { int i; };
              int f (void)
              {
                    struct s *p = 0, *q;
                    int j = 0;
              again:
                        q = p, p = &((struct s){ j++ });
                        if (j < 2) goto again;
                        return p == q && q->i == 1;
              }
     The function f() always returns the value 1.
16   Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
     lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
     have an indeterminate value, which would result in undefined behavior.

     Forward references: type names (6.7.7), initialization (6.7.9).

6.5.3 [Unary operators]


1            unary-expression:
                    postfix-expression
                    ++ unary-expression
                    -- unary-expression
                    unary-operator cast-expression
                    sizeof unary-expression
                    sizeof ( type-name )
                    _Alignof ( type-name )
             unary-operator: one of
                    & * + - ~             !

6.5.3.1 [Prefix increment and decrement operators]


1   The operand of the prefix increment or decrement operator shall have atomic, qualified,
    or unqualified real or pointer type, and shall be a modifiable lvalue.
    Semantics
2   The value of the operand of the prefix ++ operator is incremented. The result is the new
    value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
    See the discussions of additive operators and compound assignment for information on
    constraints, types, side effects, and conversions and the effects of operations on pointers.
3   The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
    operand is decremented.
    Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).

6.5.3.2 [Address and indirection operators]


1   The operand of the unary & operator shall be either a function designator, the result of a
    [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
    not declared with the register storage-class specifier.
2   The operand of the unary * operator shall have pointer type.
    Semantics
3   The unary & operator yields the address of its operand. If the operand has type ``type'',
    the result has type ``pointer to type''. If the operand is the result of a unary * operator,
    neither that operator nor the & operator is evaluated and the result is as if both were
    omitted, except that the constraints on the operators still apply and the result is not an

    lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
    the unary * that is implied by the [] is evaluated and the result is as if the & operator
    were removed and the [] operator were changed to a + operator. Otherwise, the result is
    a pointer to the object or function designated by its operand.
4   The unary * operator denotes indirection. If the operand points to a function, the result is
    a function designator; if it points to an object, the result is an lvalue designating the
    object. If the operand has type ``pointer to type'', the result has type ``type''. If an
    invalid value has been assigned to the pointer, the behavior of the unary * operator is
    undefined.102)
    Forward references: storage-class specifiers (6.7.1), structure and union specifiers
    (6.7.2.1).
Footnote 102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
         always true that if E is a function designator or an lvalue that is a valid operand of the unary &
         operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
         an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
         Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
         address inappropriately aligned for the type of object pointed to, and the address of an object after the
         end of its lifetime.

6.5.3.3 [Unary arithmetic operators]


1   The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
    integer type; of the ! operator, scalar type.
    Semantics
2   The result of the unary + operator is the value of its (promoted) operand. The integer
    promotions are performed on the operand, and the result has the promoted type.
3   The result of the unary - operator is the negative of its (promoted) operand. The integer
    promotions are performed on the operand, and the result has the promoted type.
4   The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
    each bit in the result is set if and only if the corresponding bit in the converted operand is
    not set). The integer promotions are performed on the operand, and the result has the
    promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
    to the maximum value representable in that type minus E.
5   The result of the logical negation operator ! is 0 if the value of its operand compares
    unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
    The expression !E is equivalent to (0==E).


6.5.3.4 [The sizeof and _Alignof operators]


1   The sizeof operator shall not be applied to an expression that has function type or an
    incomplete type, to the parenthesized name of such a type, or to an expression that
    designates a bit-field member. The _Alignof operator shall not be applied to a
    function type or an incomplete type.
    Semantics
2   The sizeof operator yields the size (in bytes) of its operand, which may be an
    expression or the parenthesized name of a type. The size is determined from the type of
    the operand. The result is an integer. If the type of the operand is a variable length array
    type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
    integer constant.
3   The _Alignof operator yields the alignment requirement of its operand type. The
    operand is not evaluated and the result is an integer constant. When applied to an array
    type, the result is the alignment requirement of the element type.
4   When sizeof is applied to an operand that has type char, unsigned char, or
    signed char, (or a qualified version thereof) the result is 1. When applied to an
    operand that has array type, the result is the total number of bytes in the array.103) When
    applied to an operand that has structure or union type, the result is the total number of
    bytes in such an object, including internal and trailing padding.
Footnote 103) When applied to a parameter declared to have array or function type, the sizeof operator yields the
         size of the adjusted (pointer) type (see 6.9.1).
5   The value of the result of both operators is implementation-defined, and its type (an
    unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
6   EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
    allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
    allocate and return a pointer to void. For example:
            extern void *alloc(size_t);
            double *dp = alloc(sizeof *dp);
    The implementation of the alloc function should ensure that its return value is aligned suitably for
    conversion to a pointer to double.

7   EXAMPLE 2      Another use of the sizeof operator is to compute the number of elements in an array:
            sizeof array / sizeof array[0]

8   EXAMPLE 3      In this example, the size of a variable length array is computed and returned from a
    function:
            #include <stddef.h>

             size_t fsize3(int n)
             {
                   char b[n+3];                   // variable length array
                   return sizeof b;               // execution time sizeof
             }
             int main()
             {
                   size_t size;
                   size = fsize3(10); // fsize3 returns 13
                   return 0;
             }

    Forward references: common definitions <stddef.h> (7.19), declarations (6.7),
    structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).

6.5.4 [Cast operators]


1            cast-expression:
                    unary-expression
                    ( type-name ) cast-expression
    Constraints
2   Unless the type name specifies a void type, the type name shall specify atomic, qualified,
    or unqualified scalar type, and the operand shall have scalar type.
3   Conversions that involve pointers, other than where permitted by the constraints of 6.5.16.1, 
    shall be specified by means of an explicit cast.
4   A pointer type shall not be converted to any floating type. A floating type shall not be
    converted to any pointer type.
    Semantics
5   Preceding an expression by a parenthesized type name converts the value of the
    expression to the named type. This construction is called a cast .104) A cast that specifies
    no conversion has no effect on the type or value of an expression.
Footnote 104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
         unqualified version of the type.
6   If the value of the expression is represented with greater range or precision than required
    by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
    type of the expression is the same as the named type and removes any extra range and
    precision.
    Forward references: equality operators (6.5.9), function declarators (including
    prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).


6.5.5 [Multiplicative operators]


1            multiplicative-expression:
                     cast-expression
                     multiplicative-expression * cast-expression
                     multiplicative-expression / cast-expression
                     multiplicative-expression % cast-expression
    Constraints
2   Each of the operands shall have arithmetic type. The operands of the % operator shall
    have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the binary * operator is the product of the operands.
5   The result of the / operator is the quotient from the division of the first operand by the
    second; the result of the % operator is the remainder. In both operations, if the value of
    the second operand is zero, the behavior is undefined.
6   When integers are divided, the result of the / operator is the algebraic quotient with any
    fractional part discarded.105) If the quotient a/b is representable, the expression
    (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
    undefined.
Footnote 105) This is often called ``truncation toward zero''.

6.5.6 [Additive operators]


1            additive-expression:
                    multiplicative-expression
                    additive-expression + multiplicative-expression
                    additive-expression - multiplicative-expression
    Constraints
2   For addition, either both operands shall have arithmetic type, or one operand shall be a
    pointer to a complete object type and the other shall have integer type. (Incrementing is
    equivalent to adding 1.)
3   For subtraction, one of the following shall hold:

    -- both operands have arithmetic type;
    -- both operands are pointers to qualified or unqualified versions of compatible complete
       object types; or
    -- the left operand is a pointer to a complete object type and the right operand has
       integer type.
    (Decrementing is equivalent to subtracting 1.)
    Semantics
4   If both operands have arithmetic type, the usual arithmetic conversions are performed on
    them.
5   The result of the binary + operator is the sum of the operands.
6   The result of the binary - operator is the difference resulting from the subtraction of the
    second operand from the first.
7   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.
8   When an expression that has integer type is added to or subtracted from a pointer, the
    result has the type of the pointer operand. If the pointer operand points to an element of
    an array object, and the array is large enough, the result points to an element offset from
    the original element such that the difference of the subscripts of the resulting and original
    array elements equals the integer expression. In other words, if the expression P points to
    the i -th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
    (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
    the array object, provided they exist. Moreover, if the expression P points to the last
    element of an array object, the expression (P)+1 points one past the last element of the
    array object, and if the expression Q points one past the last element of an array object,
    the expression (Q)-1 points to the last element of the array object. If both the pointer
    operand and the result point to elements of the same array object, or one past the last
    element of the array object, the evaluation shall not produce an overflow; otherwise, the
    behavior is undefined. If the result points one past the last element of the array object, it
    shall not be used as the operand of a unary * operator that is evaluated.
9   When two pointers are subtracted, both shall point to elements of the same array object,
    or one past the last element of the array object; the result is the difference of the
    subscripts of the two array elements. The size of the result is implementation-defined,
    and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
    If the result is not representable in an object of that type, the behavior is undefined. In
    other words, if the expressions P and Q point to, respectively, the i -th and j -th elements of
    an array object, the expression (P)-(Q) has the value i-j provided the value fits in an

     object of type ptrdiff_t. Moreover, if the expression P points either to an element of
     an array object or one past the last element of an array object, and the expression Q points
     to the last element of the same array object, the expression ((Q)+1)-(P) has the same
     value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
     expression P points one past the last element of the array object, even though the
     expression (Q)+1 does not point to an element of the array object.106)
Footnote 106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
          this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
          by the size of the object originally pointed to, and the resulting pointer is converted back to the
          original type. For pointer subtraction, the result of the difference between the character pointers is
          similarly divided by the size of the object originally pointed to.
          When viewed in this way, an implementation need only provide one extra byte (which may overlap
          another object in the program) just after the end of the object in order to satisfy the ``one past the last
          element'' requirements.
10   EXAMPLE        Pointer arithmetic is well defined with pointers to variable length array types.
              {
                       int n = 4, m = 3;
                       int a[n][m];
                       int (*p)[m] = a;            //   p == &a[0]
                       p += 1;                     //   p == &a[1]
                       (*p)[2] = 99;               //   a[1][2] == 99
                       n = p - a;                  //   n == 1
              }
11   If array a in the above example were declared to be an array of known constant size, and pointer p were
     declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
     the same.

     Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
     (7.19).

6.5.7 [Bitwise shift operators]


1             shift-expression:
                      additive-expression
                      shift-expression << additive-expression
                      shift-expression >> additive-expression
     Constraints
2    Each of the operands shall have integer type.
     Semantics
3    The integer promotions are performed on each of the operands. The type of the result is
     that of the promoted left operand. If the value of the right operand is negative or is

    greater than or equal to the width of the promoted left operand, the behavior is undefined.
4   The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
    zeros. If E1 has an unsigned type, the value of the result is E1 × 2E2 , reduced modulo
    one more than the maximum value representable in the result type. If E1 has a signed
    type and nonnegative value, and E1 × 2E2 is representable in the result type, then that is
    the resulting value; otherwise, the behavior is undefined.
5   The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
    or if E1 has a signed type and a nonnegative value, the value of the result is the integral
    part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
    resulting value is implementation-defined.

6.5.8 [Relational operators]


1            relational-expression:
                     shift-expression
                     relational-expression   <    shift-expression
                     relational-expression   >    shift-expression
                     relational-expression   <=   shift-expression
                     relational-expression   >=   shift-expression
    Constraints
2   One of the following shall hold:
    -- both operands have real type; or
    -- both operands are pointers to qualified or unqualified versions of compatible object
       types.
    Semantics
3   If both of the operands have arithmetic type, the usual arithmetic conversions are
    performed.
4   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.
5   When two pointers are compared, the result depends on the relative locations in the
    address space of the objects pointed to. If two pointers to object types both point to the
    same object, or both point one past the last element of the same array object, they
    compare equal. If the objects pointed to are members of the same aggregate object,
    pointers to structure members declared later compare greater than pointers to members
    declared earlier in the structure, and pointers to array elements with larger subscript
    values compare greater than pointers to elements of the same array with lower subscript

    values. All pointers to members of the same union object compare equal. If the
    expression P points to an element of an array object and the expression Q points to the
    last element of the same array object, the pointer expression Q+1 compares greater than P. 
    In all other cases, the behavior is undefined.
6   Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
    (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
    false.107) The result has type int.
Footnote 107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it
         means (a<b)<c; in other words, ``if a is less than b, compare 1 to c; otherwise, compare 0 to c''.

6.5.9 [Equality operators]


1            equality-expression:
                    relational-expression
                    equality-expression == relational-expression
                    equality-expression != relational-expression
    Constraints
2   One of the following shall hold:
    -- both operands have arithmetic type;
    -- both operands are pointers to qualified or unqualified versions of compatible types;
    -- one operand is a pointer to an object type and the other is a pointer to a qualified or
       unqualified version of void; or
    -- one operand is a pointer and the other is a null pointer constant.
    Semantics
3   The == (equal to) and != (not equal to) operators are analogous to the relational
    operators except for their lower precedence.108) Each of the operators yields 1 if the
    specified relation is true and 0 if it is false. The result has type int. For any pair of
    operands, exactly one of the relations is true.
Footnote 108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.
4   If both of the operands have arithmetic type, the usual arithmetic conversions are
    performed. Values of complex types are equal if and only if both their real parts are equal
    and also their imaginary parts are equal. Any two values of arithmetic types from
    different type domains are equal if and only if the results of their conversions to the
    (complex) result type determined by the usual arithmetic conversions are equal.

5   Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a
    null pointer constant, the null pointer constant is converted to the type of the pointer. If
    one operand is a pointer to an object type and the other is a pointer to a qualified or
    unqualified version of void, the former is converted to the type of the latter.
6   Two pointers compare equal if and only if both are null pointers, both are pointers to the
    same object (including a pointer to an object and a subobject at its beginning) or function,
    both are pointers to one past the last element of the same array object, or one is a pointer
    to one past the end of one array object and the other is a pointer to the start of a different
    array object that happens to immediately follow the first array object in the address
    space.109)
Footnote 109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
         adjacent members of a structure with no padding between them, or because the implementation chose
         to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
         outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
         behavior.
7   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.

6.5.10 [Bitwise AND operator]


1            AND-expression:
                   equality-expression
                   AND-expression & equality-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
    the result is set if and only if each of the corresponding bits in the converted operands is
    set).


6.5.11 [Bitwise exclusive OR operator]


1            exclusive-OR-expression:
                     AND-expression
                     exclusive-OR-expression ^ AND-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
    in the result is set if and only if exactly one of the corresponding bits in the converted
    operands is set).

6.5.12 [Bitwise inclusive OR operator]


1            inclusive-OR-expression:
                     exclusive-OR-expression
                     inclusive-OR-expression | exclusive-OR-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
    the result is set if and only if at least one of the corresponding bits in the converted
    operands is set).

6.5.13 [Logical AND operator]


1             logical-AND-expression:
                      inclusive-OR-expression
                      logical-AND-expression && inclusive-OR-expression
    Constraints
2   Each of the operands shall have scalar type.
    Semantics
3   The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
    yields 0. The result has type int.
4   Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
    if the second operand is evaluated, there is a sequence point between the evaluations of
    the first and second operands. If the first operand compares equal to 0, the second
    operand is not evaluated.

6.5.14 [Logical OR operator]


1             logical-OR-expression:
                      logical-AND-expression
                      logical-OR-expression || logical-AND-expression
    Constraints
2   Each of the operands shall have scalar type.
    Semantics
3   The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
    yields 0. The result has type int.
4   Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the
    second operand is evaluated, there is a sequence point between the evaluations of the first
    and second operands. If the first operand compares unequal to 0, the second operand is
    not evaluated.

6.5.15 [Conditional operator]


1            conditional-expression:
                    logical-OR-expression
                    logical-OR-expression ? expression : conditional-expression
    Constraints
2   The first operand shall have scalar type.
3   One of the following shall hold for the second and third operands:
    -- both operands have arithmetic type;
    -- both operands have the same structure or union type;
    -- both operands have void type;
    -- both operands are pointers to qualified or unqualified versions of compatible types;
    -- one operand is a pointer and the other is a null pointer constant; or
    -- one operand is a pointer to an object type and the other is a pointer to a qualified or
       unqualified version of void.
    Semantics
4   The first operand is evaluated; there is a sequence point between its evaluation and the
    evaluation of the second or third operand (whichever is evaluated). The second operand
    is evaluated only if the first compares unequal to 0; the third operand is evaluated only if
    the first compares equal to 0; the result is the value of the second or third operand
    (whichever is evaluated), converted to the type described below.110)
Footnote 110) A conditional expression does not yield an lvalue.
5   If both the second and third operands have arithmetic type, the result type that would be
    determined by the usual arithmetic conversions, were they applied to those two operands,
    is the type of the result. If both the operands have structure or union type, the result has
    that type. If both operands have void type, the result has void type.
6   If both the second and third operands are pointers or one is a null pointer constant and the
    other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers
    of the types referenced by both operands. Furthermore, if both operands are pointers to
    compatible types or to differently qualified versions of compatible types, the result type is
    a pointer to an appropriately qualified version of the composite type; if one operand is a
    null pointer constant, the result has the type of the other operand; otherwise, one operand
    is a pointer to void or a qualified version of void, in which case the result type is a
    pointer to an appropriately qualified version of void.

7   EXAMPLE The common type that results when the second and third operands are pointers is determined
    in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two
    pointers have compatible types.
8   Given the declarations
              const void *c_vp;
              void *vp;
              const int *c_ip;
              volatile int *v_ip;
              int *ip;
              const char *c_cp;
    the third column in the following table is the common type that is the result of a conditional expression in
    which the first two columns are the second and third operands (in either order):
              c_vp    c_ip      const void *
              v_ip    0         volatile int *
              c_ip    v_ip      const volatile int *
              vp      c_cp      const void *
              ip      c_ip      const int *
              vp      ip        void *


6.5.16 [Assignment operators]


1            assignment-expression:
                    conditional-expression
                    unary-expression assignment-operator assignment-expression
             assignment-operator: one of
                    = *= /= %= +=                       -=     <<=      >>=      &=     ^=     |=
    Constraints
2   An assignment operator shall have a modifiable lvalue as its left operand.
    Semantics
3   An assignment operator stores a value in the object designated by the left operand. An
    assignment expression has the value of the left operand after the assignment,111) but is not
    an lvalue. The type of an assignment expression is the type the left operand would have
    after lvalue conversion. The side effect of updating the stored value of the left operand is
    sequenced after the value computations of the left and right operands. The evaluations of
    the operands are unsequenced.

Footnote 111) The implementation is permitted to read the object to determine the value but is not required to, even
         when the object has volatile-qualified type.

6.5.16.1 [Simple assignment]


1   One of the following shall hold:112)
    -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has
       arithmetic type;
    -- the left operand has an atomic, qualified, or unqualified version of a structure or union
       type compatible with the type of the right;
    -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
       the type the left operand would have after lvalue conversion) both operands are
       pointers to qualified or unqualified versions of compatible types, and the type pointed
       to by the left has all the qualifiers of the type pointed to by the right;
    -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
       the type the left operand would have after lvalue conversion) one operand is a pointer
       to an object type, and the other is a pointer to a qualified or unqualified version of
       void, and the type pointed to by the left has all the qualifiers of the type pointed to
       by the right;
    -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null
       pointer constant; or
    -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a
       pointer.
    Semantics
Footnote 112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
         (specified in 6.3.2.1) that changes lvalues to ``the value of the expression'' and thus removes any type
         qualifiers that were applied to the type category of the expression (for example, it removes const but
         not volatile from the type int volatile * const).
2   In simple assignment (=), the value of the right operand is converted to the type of the
    assignment expression and replaces the value stored in the object designated by the left
    operand.
3   If the value being stored in an object is read from another object that overlaps in any way
    the storage of the first object, then the overlap shall be exact and the two objects shall
    have qualified or unqualified versions of a compatible type; otherwise, the behavior is
    undefined.
4   EXAMPLE 1       In the program fragment

            int f(void);
            char c;
            /* ... */
            if ((c = f()) == -1)
                    /* ... */
    the int value returned by the function may be truncated when stored in the char, and then converted back
    to int width prior to the comparison. In an implementation in which ``plain'' char has the same range of
    values as unsigned char (and char is narrower than int), the result of the conversion cannot be
    negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
    variable c should be declared as int.

5   EXAMPLE 2       In the fragment:
            char c;
            int i;
            long l;
            l = (c = i);
    the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
    of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
    that is, long int type.

6   EXAMPLE 3       Consider the fragment:
            const char **cpp;
            char *p;
            const char c = 'A';
            cpp = &p;                  // constraint violation
            *cpp = &c;                 // valid
            *p = 0;                    // valid
    The first assignment is unsafe because it would allow the following valid code to attempt to change the
    value of the const object c.


6.5.16.2 [Compound assignment]


1   For the operators += and -= only, either the left operand shall be an atomic, qualified, or
    unqualified pointer to a complete object type, and the right shall have integer type; or the
    left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
    shall have arithmetic type.
2   For the other operators, the left operand shall have atomic, qualified, or unqualified
    arithmetic type, and (considering the type the left operand would have after lvalue
    conversion) each operand shall have arithmetic type consistent with those allowed by the
    corresponding binary operator.
    Semantics
3   A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
    expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
    respect to an indeterminately-sequenced function call, the operation of a compound
    assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
    read-modify-write operation with memory_order_seq_cst memory order
    semantics.113)
     to the following code sequence where T1 is the type of E1 and T2 is the type of E2:
               T1 *addr = &E1;
               T2 val = (E2);
               T1 old = *addr;
               T1 new;
               do {
                     new = old op val;
               } while (!atomic_compare_exchange_strong(addr, &old, new));
      with new being the result of the operation.
      If E1 or E2 has floating type, then exceptional conditions or floating-point exceptions encountered
      during discarded evaluations of new should also be discarded in order to satisfy the equivalence of E1
      op = E2 and E1 = E1 op (E2). For example, if annex F is in effect, the floating types involved have
      IEC 60559 formats, and FLT_EVAL_METHOD is 0, the equivalent code would be:
               #include <fenv.h>
               #pragma STDC FENV_ACCESS ON
               /* ... */
                       fenv_t fenv;
                       T1 *addr = &E1;
                       T2 val = E2;
                       T1 old = *addr;
                       T1 new;
                       feholdexcept(&fenv);
                       for (;;) {
                             new = old op val;
                             if (atomic_compare_exchange_strong(addr, &old, new))
                                         break;
                             feclearexcept(FE_ALL_EXCEPT);
                       }
                       feupdateenv(&fenv);
      If FLT_EVAL_METHOD is not 0, then T2 must be a type with the range and precision to which E2 is
      evaluated in order to satisfy the equivalence.

Footnote 113) Where a pointer to an atomic object can be formed and E1 and E2 have integer type, this is equivalent

6.5.17 [Comma operator]


1            expression:
                    assignment-expression
                    expression , assignment-expression
    Semantics
2   The left operand of a comma operator is evaluated as a void expression; there is a
    sequence point between its evaluation and that of the right operand. Then the right
    operand is evaluated; the result has its type and value.114)
Footnote 114) A comma operator does not yield an lvalue.
3   EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
    appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
    of initializers). On the other hand, it can be used within a parenthesized expression or within the second
    expression of a conditional operator in such contexts. In the function call
              f(a, (t=3, t+2), c)
    the function has three arguments, the second of which has the value 5.

    Forward references: initialization (6.7.9).


6.6 [Constant expressions]


1            constant-expression:
                    conditional-expression
    Description
2   A constant expression can be evaluated during translation rather than runtime, and
    accordingly may be used in any place that a constant may be.
    Constraints
3   Constant expressions shall not contain assignment, increment, decrement, function-call,
    or comma operators, except when they are contained within a subexpression that is not
    evaluated.115)
Footnote 115) The operand of a sizeof or _Alignof operator is usually not evaluated (6.5.3.4).
4   Each constant expression shall evaluate to a constant that is in the range of representable
    values for its type.
    Semantics
5   An expression that evaluates to a constant is required in several contexts. If a floating
    expression is evaluated in the translation environment, the arithmetic range and precision
    shall be at least as great as if the expression were being evaluated in the execution
    environment.116)
Footnote 116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
         the translation environment.
6   An integer constant expression117) shall have integer type and shall only have operands
    that are integer constants, enumeration constants, character constants, sizeof
    expressions whose results are integer constants, _Alignof expressions, and floating
    constants that are the immediate operands of casts. Cast operators in an integer constant
    expression shall only convert arithmetic types to integer types, except as part of an
    operand to the sizeof or _Alignof operator.
Footnote 117) An integer constant expression is required in a number of contexts such as the size of a bit-field
         member of a structure, the value of an enumeration constant, and the size of a non-variable length
         array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
         preprocessing directives are discussed in 6.10.1.
7   More latitude is permitted for constant expressions in initializers. Such a constant
    expression shall be, or evaluate to, one of the following:
    -- an arithmetic constant expression,

     -- a null pointer constant,
     -- an address constant, or
     -- an address constant for a complete object type plus or minus an integer constant
        expression.
8    An arithmetic constant expression shall have arithmetic type and shall only have
     operands that are integer constants, floating constants, enumeration constants, character
     constants, sizeof expressions whose results are integer constants, and _Alignof
     expressions. Cast operators in an arithmetic constant expression shall only convert
     arithmetic types to arithmetic types, except as part of an operand to a sizeof or
     _Alignof operator.
9    An address constant is a null pointer, a pointer to an lvalue designating an object of static
     storage duration, or a pointer to a function designator; it shall be created explicitly using
     the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
     an expression of array or function type. The array-subscript [] and member-access .
     and -> operators, the address & and indirection * unary operators, and pointer casts may
     be used in the creation of an address constant, but the value of an object shall not be
     accessed by use of these operators.
10   An implementation may accept other forms of constant expressions.
11   The semantic rules for the evaluation of a constant expression are the same as for
     nonconstant expressions.118)
     Forward references: array declarators (6.7.6.2), initialization (6.7.9).

Footnote 118) Thus, in the following initialization,
                     static int i = 2 || 1 / 0;
            the expression is a valid integer constant expression with value one.

6.7 [Declarations]


1            declaration:
                    declaration-specifiers init-declarator-listopt ;
                    static_assert-declaration
             declaration-specifiers:
                    storage-class-specifier declaration-specifiersopt
                    type-specifier declaration-specifiersopt
                    type-qualifier declaration-specifiersopt
                    function-specifier declaration-specifiersopt
                    alignment-specifier declaration-specifiersopt
             init-declarator-list:
                     init-declarator
                     init-declarator-list , init-declarator
             init-declarator:
                     declarator
                     declarator = initializer
    Constraints
2   A declaration other than a static_assert declaration shall declare at least a declarator
    (other than the parameters of a function or the members of a structure or union), a tag, or
    the members of an enumeration.
3   If an identifier has no linkage, there shall be no more than one declaration of the identifier
    (in a declarator or type specifier) with the same scope and in the same name space, except
    that:
    -- a typedef name may be redefined to denote the same type as it currently does,
       provided that type is not a variably modified type;
    -- tags may be redeclared as specified in 6.7.2.3.
4   All declarations in the same scope that refer to the same object or function shall specify
    compatible types.
    Semantics
5   A declaration specifies the interpretation and attributes of a set of identifiers. A definition
    of an identifier is a declaration for that identifier that:
    -- for an object, causes storage to be reserved for that object;
    -- for a function, includes the function body;119)
    -- for an enumeration constant, is the (only) declaration of the identifier;
    -- for a typedef name, is the first (or only) declaration of the identifier.
Footnote 119) Function definitions have a different syntax, described in 6.9.1.
6   The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
    storage duration, and part of the type of the entities that the declarators denote. The init-
    declarator-list is a comma-separated sequence of declarators, each of which may have
    additional type information, or an initializer, or both. The declarators contain the
    identifiers (if any) being declared.
7   If an identifier for an object is declared with no linkage, the type for the object shall be
    complete by the end of its declarator, or by the end of its init-declarator if it has an
    initializer; in the case of function parameters (including in prototypes), it is the adjusted
    type (see 6.7.6.3) that is required to be complete.
    Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
    (6.7.9), type names (6.7.7), type qualifiers (6.7.3).

6.7.1 [Storage-class specifiers]


1            storage-class-specifier:
                    typedef
                    extern
                    static
                    _Thread_local
                    auto
                    register
    Constraints
2   At most, one storage-class specifier may be given in the declaration specifiers in a
    declaration, except that _Thread_local may appear with static or extern.120)
Footnote 120) See ``future language directions'' (6.11.5).
3   In the declaration of an object with block scope, if the declaration specifiers include
    _Thread_local, they shall also include either static or extern. If
    _Thread_local appears in any declaration of an object, it shall be present in every
    declaration of that object.
4   _Thread_local shall not appear in the declaration specifiers of a function declaration.

    Semantics
5   The typedef specifier is called a ``storage-class specifier'' for syntactic convenience
    only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
    were discussed in 6.2.2 and 6.2.4.
6   A declaration of an identifier for an object with storage-class specifier register
    suggests that access to the object be as fast as possible. The extent to which such
    suggestions are effective is implementation-defined.121)
Footnote 121) The implementation may treat any register declaration simply as an auto declaration. However,
         whether or not addressable storage is actually used, the address of any part of an object declared with
         storage-class specifier register cannot be computed, either explicitly (by use of the unary &
         operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
         6.3.2.1). Thus, the only operators that can be applied to an array declared with storage-class specifier
         register are sizeof and _Alignof.
7   The declaration of an identifier for a function that has block scope shall have no explicit
    storage-class specifier other than extern.
8   If an aggregate or union object is declared with a storage-class specifier other than
    typedef, the properties resulting from the storage-class specifier, except with respect to
    linkage, also apply to the members of the object, and so on recursively for any aggregate
    or union member objects.
    Forward references: type definitions (6.7.8).

6.7.2 [Type specifiers]


1            type-specifier:
                    void
                    char
                    short
                    int
                    long
                    float
                    double
                    signed
                    unsigned
                    _Bool
                    _Complex
                    atomic-type-specifier
                    struct-or-union-specifier
                    enum-specifier
                    typedef-name
    Constraints
2   At least one type specifier shall be given in the declaration specifiers in each declaration,
    and in the specifier-qualifier list in each struct declaration and type name. Each list of
    type specifiers shall be one of the following multisets (delimited by commas, when there
    is more than one multiset per item); the type specifiers may occur in any order, possibly
    intermixed with the other declaration specifiers.
    -- void
    -- char
    -- signed char
    -- unsigned char
    -- short, signed short, short int, or signed short int
    -- unsigned short, or unsigned short int
    -- int, signed, or signed int
    -- unsigned, or unsigned int
    -- long, signed long, long int, or signed long int
    -- unsigned long, or unsigned long int

    -- long long, signed long long, long long int, or
       signed long long int
    -- unsigned long long, or unsigned long long int
    -- float
    -- double
    -- long double
    -- _Bool
    -- float _Complex
    -- double _Complex
    -- long double _Complex
    -- atomic type specifier
    -- struct or union specifier
    -- enum specifier
    -- typedef name
3   The type specifier _Complex shall not be used if the implementation does not support
    complex types (see 6.10.8.3).
    Semantics
4   Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
    through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
    characteristics of the other types are discussed in 6.2.5.
5   Each of the comma-separated multisets designates the same type, except that for bit-
    fields, it is implementation-defined whether the specifier int designates the same type as
    signed int or the same type as unsigned int.
    Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
    structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).

6.7.2.1 [Structure and union specifiers]


1            struct-or-union-specifier:
                     struct-or-union identifieropt { struct-declaration-list }
                     struct-or-union identifier
            struct-or-union:
                    struct
                    union
            struct-declaration-list:
                    struct-declaration
                    struct-declaration-list struct-declaration
            struct-declaration:
                    specifier-qualifier-list struct-declarator-listopt ;
                    static_assert-declaration
            specifier-qualifier-list:
                    type-specifier specifier-qualifier-listopt
                    type-qualifier specifier-qualifier-listopt
            struct-declarator-list:
                    struct-declarator
                    struct-declarator-list , struct-declarator
            struct-declarator:
                    declarator
                    declaratoropt : constant-expression
    Constraints
2   A struct-declaration that does not declare an anonymous structure or anonymous union
    shall contain a struct-declarator-list.
3   A structure or union shall not contain a member with incomplete or function type (hence,
    a structure shall not contain an instance of itself, but may contain a pointer to an instance
    of itself), except that the last member of a structure with more than one named member
    may have incomplete array type; such a structure (and any union containing, possibly
    recursively, a member that is such a structure) shall not be a member of a structure or an
    element of an array.
4   The expression that specifies the width of a bit-field shall be an integer constant
    expression with a nonnegative value that does not exceed the width of an object of the
    type that would be specified were the colon and expression omitted.122) If the value is
    zero, the declaration shall have no declarator.
Footnote 122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
         value bits) of a _Bool may be just 1 bit.
5   A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
    int, unsigned int, or some other implementation-defined type. It is
    implementation-defined whether atomic types are permitted.

     Semantics
6    As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
     storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
     of members whose storage overlap.
7    Structure and union specifiers have the same form. The keywords struct and union
     indicate that the type being specified is, respectively, a structure type or a union type.
8    The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
     within a translation unit. The struct-declaration-list is a sequence of declarations for the
     members of the structure or union. If the struct-declaration-list does not contain any
     named members, either directly or via an anonymous structure or anonymous union, the
     behavior is undefined. The type is incomplete until immediately after the } that
     terminates the list, and complete thereafter.
9    A member of a structure or union may have any complete object type other than a
     variably modified type.123) In addition, a member may be declared to consist of a
     specified number of bits (including a sign bit, if any). Such a member is called a
     bit-field ;124) its width is preceded by a colon.
Footnote 123) A structure or union cannot contain a member with a variably modified type because member names
          are not ordinary identifiers as defined in 6.2.3.
Footnote 124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
          or arrays of bit-field objects.
10   A bit-field is interpreted as having a signed or unsigned integer type consisting of the
     specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of
     type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
     bit-field has the semantics of a _Bool.
Footnote 125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
          then it is implementation-defined whether the bit-field is signed or unsigned.
11   An implementation may allocate any addressable storage unit large enough to hold a bit-
     field. If enough space remains, a bit-field that immediately follows another bit-field in a
     structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
     whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
     implementation-defined. The order of allocation of bit-fields within a unit (high-order to
     low-order or low-order to high-order) is implementation-defined. The alignment of the
     addressable storage unit is unspecified.
12   A bit-field declaration with no declarator, but only a colon and a width, indicates an
     unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0

     indicates that no further bit-field is to be packed into the unit in which the previous bit-
     field, if any, was placed.
Footnote 126) An unnamed bit-field structure member is useful for padding to conform to externally imposed
          layouts.
13   An unnamed member whose type specifier is a structure specifier with no tag is called an
     anonymous structure; an unnamed member whose type specifier is a union specifier with
     no tag is called an anonymous union. The members of an anonymous structure or union
     are considered to be members of the containing structure or union. This applies
     recursively if the containing structure or union is also anonymous.
14   Each non-bit-field member of a structure or union object is aligned in an implementation-
     defined manner appropriate to its type.
15   Within a structure object, the non-bit-field members and the units in which bit-fields
     reside have addresses that increase in the order in which they are declared. A pointer to a
     structure object, suitably converted, points to its initial member (or if that member is a
     bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
     padding within a structure object, but not at its beginning.
16   The size of a union is sufficient to contain the largest of its members. The value of at
     most one of the members can be stored in a union object at any time. A pointer to a
     union object, suitably converted, points to each of its members (or if a member is a bit-
     field, then to the unit in which it resides), and vice versa.
17   There may be unnamed padding at the end of a structure or union.
18   As a special case, the last element of a structure with more than one named member may
     have an incomplete array type; this is called a flexible array member . In most situations,
     the flexible array member is ignored. In particular, the size of the structure is as if the
     flexible array member were omitted except that it may have more trailing padding than
     the omission would imply. However, when a . (or ->) operator has a left operand that is
     (a pointer to) a structure with a flexible array member and the right operand names that
     member, it behaves as if that member were replaced with the longest array (with the same
     element type) that would not make the structure larger than the object being accessed; the
     offset of the array shall remain that of the flexible array member, even if this would differ
     from that of the replacement array. If this array would have no elements, it behaves as if
     it had one element but the behavior is undefined if any attempt is made to access that
     element or to generate a pointer one past it.
19   EXAMPLE 1    The following illustrates anonymous structures and unions:
             struct v {
                   union {      // anonymous union
                          struct { int i, j; };    // anonymous structure
                          struct { long k, l; } w;
                   };
                   int m;
             } v1;
              v1.i = 2;   // valid
              v1.k = 3;   // invalid: inner structure is not anonymous
              v1.w.k = 5; // valid

20   EXAMPLE 2          After the declaration:
              struct s { int n; double d[]; };
     the structure struct s has a flexible array member d. A typical way to use this is:
              int m = /* some value */;
              struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
     and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
     p had been declared as:
              struct { int n; double d[m]; } *p;
     (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
     not be the same).
21   Following the above declaration:
              struct s t1 = { 0 };                         //   valid
              struct s t2 = { 1, { 4.2 }};                 //   invalid
              t1.n = 4;                                    //   valid
              t1.d[0] = 4.2;                               //   might be undefined behavior
     The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
     contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
              sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
     in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
     code.
22   After the further declaration:
              struct ss { int n; };
     the expressions:
              sizeof (struct s) >= sizeof (struct ss)
              sizeof (struct s) >= offsetof(struct s, d)
     are always equal to 1.
23   If sizeof (double) is 8, then after the following code is executed:
              struct s *s1;
              struct s *s2;
              s1 = malloc(sizeof (struct s) + 64);
              s2 = malloc(sizeof (struct s) + 46);
     and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
     purposes, as if the identifiers had been declared as:
              struct { int n; double d[8]; } *s1;
              struct { int n; double d[5]; } *s2;
24   Following the further successful assignments:
              s1 = malloc(sizeof (struct s) + 10);
              s2 = malloc(sizeof (struct s) + 6);
     they then behave as if the declarations were:
              struct { int n; double d[1]; } *s1, *s2;
     and:
              double *dp;
              dp = &(s1->d[0]);          //   valid
              *dp = 42;                  //   valid
              dp = &(s2->d[0]);          //   valid
              *dp = 42;                  //   undefined behavior
25   The assignment:
              *s1 = *s2;
     only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
     of the structure, they might be copied or simply overwritten with indeterminate values.

26   EXAMPLE 3 Because members of anonymous structures and unions are considered to be members of the
     containing structure or union, struct s in the following example has more than one named member and
     thus the use of a flexible array member is valid:
              struct s {
                    struct { int i; };
                    int a[];
              };

     Forward references: declarators (6.7.6), tags (6.7.2.3).

6.7.2.2 [Enumeration specifiers]


1             enum-specifier:
                    enum identifieropt { enumerator-list }
                    enum identifieropt { enumerator-list , }
                    enum identifier
              enumerator-list:
                    enumerator
                    enumerator-list , enumerator
              enumerator:
                    enumeration-constant
                    enumeration-constant = constant-expression
     Constraints
2    The expression that defines the value of an enumeration constant shall be an integer
     constant expression that has a value representable as an int.

    Semantics
3   The identifiers in an enumerator list are declared as constants that have type int and
    may appear wherever such are permitted.127) An enumerator with = defines its
    enumeration constant as the value of the constant expression. If the first enumerator has
    no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
    defines its enumeration constant as the value of the constant expression obtained by
    adding 1 to the value of the previous enumeration constant. (The use of enumerators with
    = may produce enumeration constants with values that duplicate other values in the same
    enumeration.) The enumerators of an enumeration are also known as its members.
Footnote 127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
         each other and from other identifiers declared in ordinary declarators.
4   Each enumerated type shall be compatible with char, a signed integer type, or an
    unsigned integer type. The choice of type is implementation-defined,128) but shall be
    capable of representing the values of all the members of the enumeration. The
    enumerated type is incomplete until immediately after the } that terminates the list of
    enumerator declarations, and complete thereafter.
Footnote 128) An implementation may delay the choice of which integer type until all enumeration constants have
         been seen.
5   EXAMPLE       The following fragment:
            enum hue { chartreuse, burgundy, claret=20, winedark };
            enum hue col, *cp;
            col = claret;
            cp = &col;
            if (*cp != burgundy)
                  /* ... */
    makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
    pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.

    Forward references: tags (6.7.2.3).

6.7.2.3 [Tags]


1   A specific type shall have its content defined at most once.
2   Where two declarations that use the same tag declare the same type, they shall both use
    the same choice of struct, union, or enum.
3   A type specifier of the form
            enum identifier
    without an enumerator list shall only appear after the type it specifies is complete.

    Semantics
4   All declarations of structure, union, or enumerated types that have the same scope and
    use the same tag declare the same type. Irrespective of whether there is a tag or what
    other declarations of the type are in the same translation unit, the type is incomplete129)
    until immediately after the closing brace of the list defining the content, and complete
    thereafter.
Footnote 129) An incomplete type may only by used when the size of an object of that type is not needed. It is not
         needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
         when a pointer to or a function returning a structure or union is being declared. (See incomplete types
         in 6.2.5.) The specification has to be complete before such a function is called or defined.
5   Two declarations of structure, union, or enumerated types which are in different scopes or
    use different tags declare distinct types. Each declaration of a structure, union, or
    enumerated type which does not include a tag declares a distinct type.
6   A type specifier of the form
             struct-or-union identifieropt { struct-declaration-list }
    or
             enum identifieropt { enumerator-list }
    or
             enum identifieropt { enumerator-list , }
    declares a structure, union, or enumerated type. The list defines the structure content ,
    union content , or enumeration content . If an identifier is provided,130) the type specifier
    also declares the identifier to be the tag of that type.
Footnote 130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
         of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
         can make use of that typedef name to declare objects having the specified structure, union, or
         enumerated type.
7   A declaration of the form
             struct-or-union identifier ;
    specifies a structure or union type and declares the identifier as a tag of that type.131)
Footnote 131) A similar construction with enum does not exist.
8   If a type specifier of the form
             struct-or-union identifier
    occurs other than as part of one of the above forms, and no other declaration of the
    identifier as a tag is visible, then it declares an incomplete structure or union type, and
    declares the identifier as the tag of that type.131)

Footnote 131) A similar construction with enum does not exist.
9    If a type specifier of the form
              struct-or-union identifier
     or
              enum identifier
     occurs other than as part of one of the above forms, and a declaration of the identifier as a
     tag is visible, then it specifies the same type as that other declaration, and does not
     redeclare the tag.
10   EXAMPLE 1       This mechanism allows declaration of a self-referential structure.
              struct tnode {
                    int count;
                    struct tnode *left, *right;
              };
     specifies a structure that contains an integer and two pointers to objects of the same type. Once this
     declaration has been given, the declaration
              struct tnode s, *sp;
     declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
     these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
     which sp points; the expression s.right->count designates the count member of the right struct
     tnode pointed to from s.
11   The following alternative formulation uses the typedef mechanism:
              typedef struct tnode TNODE;
              struct tnode {
                    int count;
                    TNODE *left, *right;
              };
              TNODE s, *sp;

12   EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
     structures, the declarations
              struct s1 { struct s2 *s2p; /* ... */ }; // D1
              struct s2 { struct s1 *s1p; /* ... */ }; // D2
     specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
     declared as a tag in an enclosing scope, the declaration D1 would refer to it , not to the tag s2 declared in
     D2. To eliminate this context sensitivity, the declaration
              struct s2;
     may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
     completes the specification of the new type.

     Forward references: declarators (6.7.6), type definitions (6.7.8).

6.7.2.4 [Atomic type specifiers]


1            atomic-type-specifier:
                    _Atomic ( type-name )
    Constraints
2   Atomic type specifiers shall not be used if the implementation does not support atomic
    types (see 6.10.8.3).
3   The type name in an atomic type specifier shall not refer to an array type, a function type,
    an atomic type, or a qualified type.
    Semantics
4   The properties associated with atomic types are meaningful only for expressions that are
    lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
    interpreted as a type specifier (with a type name), not as a type qualifier.

6.7.3 [Type qualifiers]


1            type-qualifier:
                    const
                    restrict
                    volatile
                    _Atomic
    Constraints
2   Types other than pointer types whose referenced type is an object type shall not be
    restrict-qualified.
3   The type modified by the _Atomic qualifier shall not be an array type or a function
    type.
    Semantics
4   The properties associated with qualified types are meaningful only for expressions that
    are lvalues.132)
Footnote 132) The implementation may place a const object that is not volatile in a read-only region of
         storage. Moreover, the implementation need not allocate storage for such an object if its address is
         never used.
5   If the same qualifier appears more than once in the same specifier-qualifier-list , either
    directly or via one or more typedefs, the behavior is the same as if it appeared only
    once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-

     list , the resulting type is the so-qualified atomic type.
6    If an attempt is made to modify an object defined with a const-qualified type through use
     of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
     made to refer to an object defined with a volatile-qualified type through use of an lvalue
     with non-volatile-qualified type, the behavior is undefined.133)
Footnote 133) This applies to those objects that behave as if they were defined with qualified types, even if they are
          never actually defined as objects in the program (such as an object at a memory-mapped input/output
          address).
7    An object that has volatile-qualified type may be modified in ways unknown to the
     implementation or have other unknown side effects. Therefore any expression referring
     to such an object shall be evaluated strictly according to the rules of the abstract machine,
     as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
     object shall agree with that prescribed by the abstract machine, except as modified by the
     unknown factors mentioned previously.134) What constitutes an access to an object that
     has volatile-qualified type is implementation-defined.
Footnote 134) A volatile declaration may be used to describe an object corresponding to a memory-mapped
          input/output port or an object accessed by an asynchronously interrupting function. Actions on
          objects so declared shall not be ``optimized out'' by an implementation or reordered except as
          permitted by the rules for evaluating expressions.
8    An object that is accessed through a restrict-qualified pointer has a special association
     with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
     that object use, directly or indirectly, the value of that particular pointer.135) The intended
     use of the restrict qualifier (like the register storage class) is to promote
     optimization, and deleting all instances of the qualifier from all preprocessing translation
     units composing a conforming program does not change its meaning (i.e., observable
     behavior).
Footnote 135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
          association between the allocated object and the pointer.
9    If the specification of an array type includes any type qualifiers, the element type is so-
     qualified, not the array type. If the specification of a function type includes any type
     qualifiers, the behavior is undefined.136)
Footnote 136) Both of these can occur through the use of typedefs.
10   For two qualified types to be compatible, both shall have the identically qualified version
     of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
     does not affect the specified type.
11   EXAMPLE 1       An object declared
              extern const volatile int real_time_clock;

     may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.

12   EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
     modify an aggregate type:
              const struct s { int mem; } cs = { 1 };
              struct s ncs; // the object ncs is modifiable
              typedef int A[2][3];
              const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
              int *pi;
              const int *pci;
              ncs = cs;               //   valid
              cs = ncs;               //   violates modifiable lvalue constraint for =
              pi = &ncs.mem;          //   valid
              pi = &cs.mem;           //   violates type constraints for =
              pci = &cs.mem;          //   valid
              pi = a[0];              //   invalid: a[0] has type ``const int *''

13   EXAMPLE 3        The declaration
              _Atomic volatile int *p;
     specifies that p has the type ``pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type.

6.7.3.1 [Formal definition of restrict]


1    Let D be a declaration of an ordinary identifier that provides a means of designating an
     object P as a restrict-qualified pointer to type T.
2    If D appears inside a block and does not have storage class extern, let B denote the
     block. If D appears in the list of parameter declarations of a function definition, let B
     denote the associated block. Otherwise, let B denote the block of main (or the block of
     whatever function is called at program startup in a freestanding environment).
3    In what follows, a pointer expression E is said to be based on object P if (at some
     sequence point in the execution of B prior to the evaluation of E) modifying P to point to
     a copy of the array object into which it formerly pointed would change the value of E.137)
     Note that ``based'' is defined only for expressions with pointer types.
Footnote 137) In other words, E depends on the value of P itself rather than on the value of an object referenced
          indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
          expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
          expressions *p and p[1] are not.
4    During each execution of B, let L be any lvalue that has &L based on P. If L is used to
     access the value of the object X that it designates, and X is also modified (by any means),
     then the following requirements apply: T shall not be const-qualified. Every other lvalue
     used to access the value of X shall also have its address based on P. Every access that
     modifies X shall be considered also to modify P, for the purposes of this subclause. If P
     is assigned the value of a pointer expression E that is based on another restricted pointer

     object P2, associated with block B2, then either the execution of B2 shall begin before
     the execution of B, or the execution of B2 shall end prior to the assignment. If these
     requirements are not met, then the behavior is undefined.
5    Here an execution of B means that portion of the execution of the program that would
     correspond to the lifetime of an object with scalar type and automatic storage duration
     associated with B.
6    A translator is free to ignore any or all aliasing implications of uses of restrict.
7    EXAMPLE 1       The file scope declarations
              int * restrict a;
              int * restrict b;
              extern int c[];
     assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
     program, then it is never accessed using either of the other two.

8    EXAMPLE 2       The function parameter declarations in the following example
              void f(int n, int * restrict p, int * restrict q)
              {
                    while (n-- > 0)
                          *p++ = *q++;
              }
     assert that, during each execution of the function, if an object is accessed through one of the pointer
     parameters, then it is not also accessed through the other.
9    The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
     analysis of function f without examining any of the calls of f in the program. The cost is that the
     programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
     second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
     both p and q.
              void g(void)
              {
                    extern int d[100];
                    f(50, d + 50, d); // valid
                    f(50, d + 1, d); // undefined behavior
              }

10   EXAMPLE 3       The function parameter declarations
              void h(int n, int * restrict p, int * restrict q, int * restrict r)
              {
                    int i;
                    for (i = 0; i < n; i++)
                           p[i] = q[i] + r[i];
              }
     illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
     are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
     modified within function h.
11   EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
     function call and an equivalent nested block. With one exception, only ``outer-to-inner'' assignments
     between restricted pointers declared in nested blocks have defined behavior.
              {
                       int * restrict p1;
                       int * restrict q1;
                       p1 = q1; // undefined behavior
                       {
                             int * restrict p2 = p1; // valid
                             int * restrict q2 = q1; // valid
                             p1 = q2;                 // undefined behavior
                             p2 = q2;                 // undefined behavior
                       }
              }
12   The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
     precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
     example, this permits new_vector to return a vector.
              typedef struct { int n; float * restrict v; } vector;
              vector new_vector(int n)
              {
                    vector t;
                    t.n = n;
                    t.v = malloc(n * sizeof (float));
                    return t;
              }

6.7.4 [Function specifiers]


1             function-specifier:
                     inline
                     _Noreturn
     Constraints
2    Function specifiers shall be used only in the declaration of an identifier for a function.
3    An inline definition of a function with external linkage shall not contain a definition of a
     modifiable object with static or thread storage duration, and shall not contain a reference
     to an identifier with internal linkage.
4    In a hosted environment, no function specifier(s) shall appear in a declaration of main.
     Semantics
5    A function specifier may appear more than once; the behavior is the same as if it
     appeared only once.
6    A function declared with an inline function specifier is an inline function. Making a
     function an inline function suggests that calls to the function be as fast as possible.138)

     The extent to which such suggestions are effective is implementation-defined.139)
Footnote 138) By using, for example, an alternative to the usual function call mechanism, such as ``inline
          substitution''. Inline substitution is not textual substitution, nor does it create a new function.
          Therefore, for example, the expansion of a macro used within the body of the function uses the
          definition it had at the point the function body appears, and not where the function is called; and
          identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
          single address, regardless of the number of inline definitions that occur in addition to the external
          definition.
Footnote 139) For example, an implementation might never perform inline substitution, or might only perform inline
          substitutions to calls in the scope of an inline declaration.
7    Any function with internal linkage can be an inline function. For a function with external
     linkage, the following restrictions apply: If a function is declared with an inline
     function specifier, then it shall also be defined in the same translation unit. If all of the
     file scope declarations for a function in a translation unit include the inline function
     specifier without extern, then the definition in that translation unit is an inline
     definition. An inline definition does not provide an external definition for the function,
     and does not forbid an external definition in another translation unit. An inline definition
     provides an alternative to an external definition, which a translator may use to implement
     any call to the function in the same translation unit. It is unspecified whether a call to the
     function uses the inline definition or the external definition.140)
Footnote 140) Since an inline definition is distinct from the corresponding external definition and from any other
          corresponding inline definitions in other translation units, all corresponding objects with static storage
          duration are also distinct in each of the definitions.
8    A function declared with a _Noreturn function specifier shall not return to its caller.
     Recommended practice
9    The implementation should produce a diagnostic message for a function declared with a
     _Noreturn function specifier that appears to be capable of returning to its caller.
10   EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
     definition, or a definition available for use only within the translation unit. A file scope declaration with
     extern creates an external definition. The following example shows an entire translation unit.
              inline double fahr(double t)
              {
                    return (9.0 * t) / 5.0 + 32.0;
              }
              inline double cels(double t)
              {
                    return (5.0 * (t - 32.0)) / 9.0;
              }
              extern double fahr(double);                   // creates an external definition

              double convert(int is_fahr, double temp)
              {
                    /* A translator may perform inline substitutions */
                    return is_fahr ? cels(temp) : fahr(temp);
              }
11   Note that the definition of fahr is an external definition because fahr is also declared with extern, but
     the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
     external definition has to appear in another translation unit (see 6.9); the inline definition and the external
     definition are distinct and either may be used for the call.

12   EXAMPLE 2
              _Noreturn void f () {
                    abort(); // ok
              }
              _Noreturn void g (int i) { // causes undefined behavior if i <= 0
                    if (i > 0) abort();
              }

     Forward references: function definitions (6.9.1).

6.7.5 [Alignment specifier]


1             alignment-specifier:
                     _Alignas ( type-name )
                    _Alignas ( constant-expression )
     Constraints
2    An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
     a function, or a parameter, or an object declared with the register storage-class
     specifier.
3    The constant expression shall be an integer constant expression. It shall evaluate to a
     valid fundamental alignment, or to a valid extended alignment supported by the
     implementation in the context in which it appears, or to zero.
4    The combined effect of all alignment attributes in a declaration shall not specify an
     alignment that is less strict than the alignment that would otherwise be required for the
     type of the object or member being declared.
     Semantics
5    The first form is equivalent to _Alignas (_Alignof (type-name)).
6    The alignment requirement of the declared object or member is taken to be the specified
     alignment. An alignment specification of zero has no effect.141) When multiple
     alignment specifiers occur in a declaration, the effective alignment requirement is the
     strictest specified alignment.

Footnote 141) An alignment specification of zero also does not affect other alignment specifications in the same
         declaration.
7   If the definition of an object has an alignment specifier, any other declaration of that
    object shall either specify equivalent alignment or have no alignment specifier. If the
    definition of an object does not have an alignment specifier, any other declaration of that
    object shall also have no alignment specifier. If declarations of an object in different
    translation units have different alignment specifiers, the behavior is undefined.

6.7.6 [Declarators]


1            declarator:
                    pointeropt direct-declarator
             direct-declarator:
                     identifier
                     ( declarator )
                     direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
                     direct-declarator [ static type-qualifier-listopt assignment-expression ]
                     direct-declarator [ type-qualifier-list static assignment-expression ]
                     direct-declarator [ type-qualifier-listopt * ]
                     direct-declarator ( parameter-type-list )
                     direct-declarator ( identifier-listopt )
             pointer:
                    * type-qualifier-listopt
                    * type-qualifier-listopt pointer
             type-qualifier-list:
                    type-qualifier
                    type-qualifier-list type-qualifier
             parameter-type-list:
                   parameter-list
                   parameter-list , ...
             parameter-list:
                   parameter-declaration
                   parameter-list , parameter-declaration
             parameter-declaration:
                   declaration-specifiers declarator
                   declaration-specifiers abstract-declaratoropt

             identifier-list:
                     identifier
                     identifier-list , identifier
    Semantics
2   Each declarator declares one identifier, and asserts that when an operand of the same
    form as the declarator appears in an expression, it designates a function or object with the
    scope, storage duration, and type indicated by the declaration specifiers.
3   A full declarator is a declarator that is not part of another declarator. The end of a full
    declarator is a sequence point. If, in the nested sequence of declarators in a full
    declarator, there is a declarator specifying a variable length array type, the type specified
    by the full declarator is said to be variably modified . Furthermore, any type derived by
    declarator type derivation from a variably modified type is itself variably modified.
4   In the following subclauses, consider a declaration
             T D1
    where T contains the declaration specifiers that specify a type T (such as int) and D1 is
    a declarator that contains an identifier ident . The type specified for the identifier ident in
    the various forms of declarator is described inductively using this notation.
5   If, in the declaration ``T D1'', D1 has the form
             identifier
    then the type specified for ident is T .
6   If, in the declaration ``T D1'', D1 has the form
             ( D )
    then ident has the type specified by the declaration ``T D''. Thus, a declarator in
    parentheses is identical to the unparenthesized declarator, but the binding of complicated
    declarators may be altered by parentheses.
    Implementation limits
7   As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
    function declarators that modify an arithmetic, structure, union, or void type, either
    directly or via one or more typedefs.
    Forward references: array declarators (6.7.6.2), type definitions (6.7.8).

6.7.6.1 [Pointer declarators]


1   If, in the declaration ``T D1'', D1 has the form
            * type-qualifier-listopt D
    and the type specified for ident in the declaration ``T D'' is `` derived-declarator-type-list
    T '', then the type specified for ident is `` derived-declarator-type-list type-qualifier-list
    pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
2   For two pointer types to be compatible, both shall be identically qualified and both shall
    be pointers to compatible types.
3   EXAMPLE The following pair of declarations demonstrates the difference between a ``variable pointer
    to a constant value'' and a ``constant pointer to a variable value''.
            const int *ptr_to_constant;
            int *const constant_ptr;
    The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
    but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
    int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
    same location.
4   The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
    type ``pointer to int''.
            typedef int *int_ptr;
            const int_ptr constant_ptr;
    declares constant_ptr as an object that has type ``const-qualified pointer to int''.


6.7.6.2 [Array declarators]


1   In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
    an expression or *. If they delimit an expression (which specifies the size of an array), the
    expression shall have an integer type. If the expression is a constant expression, it shall
    have a value greater than zero. The element type shall not be an incomplete or function
    type. The optional type qualifiers and the keyword static shall appear only in a
    declaration of a function parameter with an array type, and then only in the outermost
    array type derivation.
2   If an identifier is declared as having a variably modified type, it shall be an ordinary
    identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
    prototype scope. If an identifier is declared to be an object with static or thread storage
    duration, it shall not have a variable length array type.
    Semantics
3   If, in the declaration ``T D1'', D1 has one of the forms:
             D[ type-qualifier-listopt assignment-expressionopt ]
             D[ static type-qualifier-listopt assignment-expression ]
             D[ type-qualifier-list static assignment-expression ]
             D[ type-qualifier-listopt * ]
    and the type specified for ident in the declaration ``T D'' is `` derived-declarator-type-list
    T '', then the type specified for ident is `` derived-declarator-type-list array of T ''.142)
    (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
Footnote 142) When several ``array of'' specifications are adjacent, a multidimensional array is declared.
4   If the size is not present, the array type is an incomplete type. If the size is * instead of
    being an expression, the array type is a variable length array type of unspecified size,
    which can only be used in declarations or type names with function prototype scope;143)
    such arrays are nonetheless complete types. If the size is an integer constant expression
    and the element type has a known constant size, the array type is not a variable length
    array type; otherwise, the array type is a variable length array type. (Variable length
    arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
Footnote 143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).
5   If the size is an expression that is not an integer constant expression: if it occurs in a
    declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
    each time it is evaluated it shall have a value greater than zero. The size of each instance
    of a variable length array type does not change during its lifetime. Where a size
    expression is part of the operand of a sizeof operator and changing the value of the
    size expression would not affect the result of the operator, it is unspecified whether or not
    the size expression is evaluated.
6   For two array types to be compatible, both shall have compatible element types, and if
    both size specifiers are present, and are integer constant expressions, then both size
    specifiers shall have the same constant value. If the two array types are used in a context
    which requires them to be compatible, it is undefined behavior if the two size specifiers
    evaluate to unequal values.
7   EXAMPLE 1
             float fa[11], *afp[17];
    declares an array of float numbers and an array of pointers to float numbers.

8   EXAMPLE 2       Note the distinction between the declarations

              extern int *x;
              extern int y[];
     The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
     (an incomplete type), the storage for which is defined elsewhere.

9    EXAMPLE 3       The following declarations demonstrate the compatibility rules for variably modified types.
              extern int n;
              extern int m;
              void fcompat(void)
              {
                    int a[n][6][m];
                    int (*p)[4][n+1];
                    int c[n][n][6][m];
                    int (*r)[n][n][n+1];
                    p = a;       // invalid: not compatible because 4 != 6
                    r = c;       // compatible, but defined behavior only if
                                 // n == 6 and m == n+1
              }

10   EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
     function prototype scope. Array objects declared with the _Thread_local, static, or extern
     storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
     the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
     identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
     structures or unions.
              extern int n;
              int A[n];                                             // invalid: file scope VLA
              extern int (*p2)[n];                                  // invalid: file scope VM
              int B[100];                                           // valid: file scope but not VM
              void fvla(int m, int C[m][m]);                        // valid: VLA with prototype scope
              void fvla(int m, int C[m][m])                         // valid: adjusted to auto pointer to VLA
              {
                    typedef int VLA[m][m];                          // valid: block scope typedef VLA
                       struct tag {
                             int (*y)[n];                           // invalid: y not ordinary identifier
                             int z[n];                              // invalid: z not ordinary identifier
                       };
                       int D[m];                                    //   valid: auto VLA
                       static int E[m];                             //   invalid: static block scope VLA
                       extern int F[m];                             //   invalid: F has linkage and is VLA
                       int (*s)[m];                                 //   valid: auto pointer to VLA
                       extern int (*r)[m];                          //   invalid: r has linkage and points to VLA
                       static int (*q)[m] = &B;                     //   valid: q is a static block pointer to VLA
              }

     Forward references:           function declarators (6.7.6.3), function definitions (6.9.1),
     initialization (6.7.9).

6.7.6.3 [Function declarators (including prototypes)]


1    A function declarator shall not specify a return type that is a function type or an array
     type.
2    The only storage-class specifier that shall occur in a parameter declaration is register.
3    An identifier list in a function declarator that is not part of a definition of that function
     shall be empty.
4    After adjustment, the parameters in a parameter type list in a function declarator that is
     part of a definition of that function shall not have incomplete type.
     Semantics
5    If, in the declaration ``T D1'', D1 has the form
             D( parameter-type-list )
     or
             D( identifier-listopt )
     and the type specified for ident in the declaration ``T D'' is `` derived-declarator-type-list
     T '', then the type specified for ident is `` derived-declarator-type-list function returning
     T ''.
6    A parameter type list specifies the types of, and may declare identifiers for, the
     parameters of the function.
7    A declaration of a parameter as ``array of type'' shall be adjusted to ``qualified pointer to
     type'', where the type qualifiers (if any) are those specified within the [ and ] of the
     array type derivation. If the keyword static also appears within the [ and ] of the
     array type derivation, then for each call to the function, the value of the corresponding
     actual argument shall provide access to the first element of an array with at least as many
     elements as specified by the size expression.
8    A declaration of a parameter as ``function returning type'' shall be adjusted to ``pointer to
     function returning type'', as in 6.3.2.1.
9    If the list terminates with an ellipsis (, ...), no information about the number or types
     of the parameters after the comma is supplied.144)
Footnote 144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
          correspond to the ellipsis.
10   The special case of an unnamed parameter of type void as the only item in the list
     specifies that the function has no parameters.

11   If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
     parameter name, it shall be taken as a typedef name.
12   If the function declarator is not part of a definition of that function, parameters may have
     incomplete type and may use the [*] notation in their sequences of declarator specifiers
     to specify variable length array types.
13   The storage-class specifier in the declaration specifiers for a parameter declaration, if
     present, is ignored unless the declared parameter is one of the members of the parameter
     type list for a function definition.
14   An identifier list declares only the identifiers of the parameters of the function. An empty
     list in a function declarator that is part of a definition of that function specifies that the
     function has no parameters. The empty list in a function declarator that is not part of a
     definition of that function specifies that no information about the number or types of the
     parameters is supplied.145)
Footnote 145) See ``future language directions'' (6.11.6).
15   For two function types to be compatible, both shall specify compatible return types.146)
     Moreover, the parameter type lists, if both are present, shall agree in the number of
     parameters and in use of the ellipsis terminator; corresponding parameters shall have
     compatible types. If one type has a parameter type list and the other type is specified by a
     function declarator that is not part of a function definition and that contains an empty
     identifier list, the parameter list shall not have an ellipsis terminator and the type of each
     parameter shall be compatible with the type that results from the application of the
     default argument promotions. If one type has a parameter type list and the other type is
     specified by a function definition that contains a (possibly empty) identifier list, both shall
     agree in the number of parameters, and the type of each prototype parameter shall be
     compatible with the type that results from the application of the default argument
     promotions to the type of the corresponding identifier. (In the determination of type
     compatibility and of a composite type, each parameter declared with function or array
     type is taken as having the adjusted type and each parameter declared with qualified type
     is taken as having the unqualified version of its declared type.)
Footnote 146) If both function types are ``old style'', parameter types are not compared.
16   EXAMPLE 1       The declaration
              int f(void), *fip(), (*pfi)();
     declares a function f with no parameters returning an int, a function fip with no parameter specification
     returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
     int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
     declaration suggests, and the same construction in an expression requires, the calling of a function fip,
     and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
     extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function

     designator, which is then used to call the function; it returns an int.
17   If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
     declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
     internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
     the identifier of the pointer pfi has block scope and no linkage.

18   EXAMPLE 2        The declaration
               int (*apfi[3])(int *x, int *y);
     declares an array apfi of three pointers to functions returning int. Each of these functions has two
     parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
     go out of scope at the end of the declaration of apfi.

19   EXAMPLE 3        The declaration
               int (*fpfi(int (*)(long), int))(int, ...);
     declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
     parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
     The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more
     additional arguments of any type.

20   EXAMPLE 4        The following prototype has a variably modified parameter.
               void addscalar(int n, int m,
                     double a[n][n*m+300], double x);
               int main()
               {
                     double b[4][308];
                     addscalar(4, 2, b, 2.17);
                     return 0;
               }
               void addscalar(int n, int m,
                     double a[n][n*m+300], double x)
               {
                     for (int i = 0; i < n; i++)
                           for (int j = 0, k = n*m+300; j < k; j++)
                                 // a is a pointer to a VLA with n*m+300 elements
                                 a[i][j] += x;
               }

21   EXAMPLE 5        The following are all compatible function prototype declarators.
               double    maximum(int       n,   int   m,   double     a[n][m]);
               double    maximum(int       n,   int   m,   double     a[*][*]);
               double    maximum(int       n,   int   m,   double     a[ ][*]);
               double    maximum(int       n,   int   m,   double     a[ ][m]);
     as are:
               void   f(double      (* restrict a)[5]);
               void   f(double      a[restrict][5]);
               void   f(double      a[restrict 3][5]);
               void   f(double      a[restrict static 3][5]);
    (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
    non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)

    Forward references: function definitions (6.9.1), type names (6.7.7).

6.7.7 [Type names]


1            type-name:
                    specifier-qualifier-list abstract-declaratoropt
             abstract-declarator:
                    pointer
                    pointeropt direct-abstract-declarator
             direct-abstract-declarator:
                     ( abstract-declarator )
                     direct-abstract-declaratoropt [ type-qualifier-listopt
                                    assignment-expressionopt ]
                     direct-abstract-declaratoropt [ static type-qualifier-listopt
                                    assignment-expression ]
                     direct-abstract-declaratoropt [ type-qualifier-list static
                                    assignment-expression ]
                     direct-abstract-declaratoropt [ * ]
                     direct-abstract-declaratoropt ( parameter-type-listopt )
    Semantics
2   In several contexts, it is necessary to specify a type. This is accomplished using a type
    name, which is syntactically a declaration for a function or an object of that type that
    omits the identifier.147)
Footnote 147) As indicated by the syntax, empty parentheses in a type name are interpreted as ``function with no
         parameter specification'', rather than redundant parentheses around the omitted identifier.
3   EXAMPLE        The constructions
             (a)      int
             (b)      int   *
             (c)      int   *[3]
             (d)      int   (*)[3]
             (e)      int   (*)[*]
             (f)      int   *()
             (g)      int   (*)(void)
             (h)      int   (*const [])(unsigned int, ...)
    name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
    array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
    with no parameter specification returning a pointer to int, (g) pointer to function with no parameters

    returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
    parameter that has type unsigned int and an unspecified number of other parameters, returning an
    int.


6.7.8 [Type definitions]


1            typedef-name:
                    identifier
    Constraints
2   If a typedef name specifies a variably modified type then it shall have block scope.
    Semantics
3   In a declaration whose storage-class specifier is typedef, each declarator defines an
    identifier to be a typedef name that denotes the type specified for the identifier in the way
    described in 6.7.6. Any array size expressions associated with variable length array
    declarators are evaluated each time the declaration of the typedef name is reached in the
    order of execution. A typedef declaration does not introduce a new type, only a
    synonym for the type so specified. That is, in the following declarations:
             typedef T type_ident;
             type_ident D;
    type_ident is defined as a typedef name with the type specified by the declaration
    specifiers in T (known as T ), and the identifier in D has the type `` derived-declarator-
    type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
    typedef name shares the same name space as other identifiers declared in ordinary
    declarators.
4   EXAMPLE 1       After
             typedef int MILES, KLICKSP();
             typedef struct { double hi, lo; } range;
    the constructions
             MILES distance;
             extern KLICKSP *metricp;
             range x;
             range z, *zp;
    are all valid declarations. The type of distance is int, that of metricp is ``pointer to function with no
    parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
    such a structure. The object distance has a type compatible with any other int object.

5   EXAMPLE 2       After the declarations
             typedef struct s1 { int x; } t1, *tp1;
             typedef struct s2 { int x; } t2, *tp2;
    type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct

    s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.

6   EXAMPLE 3       The following obscure constructions
             typedef signed int t;
             typedef int plain;
             struct tag {
                   unsigned t:4;
                   const t:5;
                   plain r:5;
             };
    declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
    with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
    qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
    [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
    (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
    unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
    type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
    in an inner scope by
             t f(t (t));
             long t;
    then a function f is declared with type ``function returning signed int with one unnamed parameter
    with type pointer to function returning signed int with one unnamed parameter with type signed
    int'', and an identifier t with type long int.

7   EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
    following declarations of the signal function specify exactly the same type, the first without making use
    of any typedef names.
             typedef void fv(int), (*pfv)(int);
             void (*signal(int, void (*)(int)))(int);
             fv *signal(int, fv *);
             pfv signal(int, pfv);

8   EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
    time the typedef name is defined, not each time it is used:
             void copyt(int n)
             {
                   typedef int B[n];   //                B is n ints, n evaluated now
                   n += 1;
                   B a;                //                a is n ints, n without += 1
                   int b[n];           //                a and b are different sizes
                   for (int i = 1; i < n;                i++)
                         a[i-1] = b[i];
             }

6.7.9 [Initialization]


1            initializer:
                      assignment-expression
                      { initializer-list }
                      { initializer-list , }
             initializer-list:
                      designationopt initializer
                      initializer-list , designationopt initializer
             designation:
                    designator-list =
             designator-list:
                    designator
                    designator-list designator
             designator:
                    [ constant-expression ]
                    . identifier
    Constraints
2   No initializer shall attempt to provide a value for an object not contained within the entity
    being initialized.
3   The type of the entity to be initialized shall be an array of unknown size or a complete
    object type that is not a variable length array type.
4   All the expressions in an initializer for an object that has static or thread storage duration
    shall be constant expressions or string literals.
5   If the declaration of an identifier has block scope, and the identifier has external or
    internal linkage, the declaration shall have no initializer for the identifier.
6   If a designator has the form
             [ constant-expression ]
    then the current object (defined below) shall have array type and the expression shall be
    an integer constant expression. If the array is of unknown size, any nonnegative value is
    valid.
7   If a designator has the form
             . identifier
    then the current object (defined below) shall have structure or union type and the
    identifier shall be the name of a member of that type.
     Semantics
8    An initializer specifies the initial value stored in an object.
9    Except where explicitly stated otherwise, for the purposes of this subclause unnamed
     members of objects of structure and union type do not participate in initialization.
     Unnamed members of structure objects have indeterminate value even after initialization.
10   If an object that has automatic storage duration is not initialized explicitly, its value is
     indeterminate. If an object that has static or thread storage duration is not initialized
     explicitly, then:
     -- if it has pointer type, it is initialized to a null pointer;
     -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
     -- if it is an aggregate, every member is initialized (recursively) according to these rules,
        and any padding is initialized to zero bits;
     -- if it is a union, the first named member is initialized (recursively) according to these
        rules, and any padding is initialized to zero bits;
11   The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
     initial value of the object is that of the expression (after conversion); the same type
     constraints and conversions as for simple assignment apply, taking the type of the scalar
     to be the unqualified version of its declared type.
12   The rest of this subclause deals with initializers for objects that have aggregate or union
     type.
13   The initializer for a structure or union object that has automatic storage duration shall be
     either an initializer list as described below, or a single expression that has compatible
     structure or union type. In the latter case, the initial value of the object, including
     unnamed members, is that of the expression.
14   An array of character type may be initialized by a character string literal or UTF-8 string
     literal, optionally enclosed in braces. Successive bytes of the string literal (including the
     terminating null character if there is room or if the array is of unknown size) initialize the
     elements of the array.
15   An array with element type compatible with a qualified or unqualified version of
     wchar_t, char16_t, or char32_t may be initialized by a wide string literal with
     the corresponding encoding prefix (L, u, or U, respectively), optionally enclosed in
     braces. Successive wide characters of the wide string literal (including the terminating
     null wide character if there is room or if the array is of unknown size) initialize the
     elements of the array.
16   Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
     enclosed list of initializers for the elements or named members.

17   Each brace-enclosed initializer list has an associated current object . When no
     designations are present, subobjects of the current object are initialized in order according
     to the type of the current object: array elements in increasing subscript order, structure
     members in declaration order, and the first named member of a union.148) In contrast, a
     designation causes the following initializer to begin initialization of the subobject
     described by the designator. Initialization then continues forward in order, beginning
     with the next subobject after that described by the designator.149)
Footnote 148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
          subobjects are initialized as usual, but the subaggregate or contained union does not become the
          current object: current objects are associated only with brace-enclosed initializer lists.
Footnote 149) After a union member is initialized, the next object is not the next member of the union; instead, it is
          the next subobject of an object containing the union.
18   Each designator list begins its description with the current object associated with the
     closest surrounding brace pair. Each item in the designator list (in order) specifies a
     particular member of its current object and changes the current object for the next
     designator (if any) to be that member.150) The current object that results at the end of the
     designator list is the subobject to be initialized by the following initializer.
Footnote 150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
          the surrounding brace pair. Note, too, that each separate designator list is independent.
19   The initialization shall occur in initializer list order, each initializer provided for a
     particular subobject overriding any previously listed initializer for the same subobject;151)
     all subobjects that are not initialized explicitly shall be initialized implicitly the same as
     objects that have static storage duration.
Footnote 151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
          not be evaluated at all.
20   If the aggregate or union contains elements or members that are aggregates or unions,
     these rules apply recursively to the subaggregates or contained unions. If the initializer of
     a subaggregate or contained union begins with a left brace, the initializers enclosed by
     that brace and its matching right brace initialize the elements or members of the
     subaggregate or the contained union. Otherwise, only enough initializers from the list are
     taken to account for the elements or members of the subaggregate or the first member of
     the contained union; any remaining initializers are left to initialize the next element or
     member of the aggregate of which the current subaggregate or contained union is a part.
21   If there are fewer initializers in a brace-enclosed list than there are elements or members
     of an aggregate, or fewer characters in a string literal used to initialize an array of known
     size than there are elements in the array, the remainder of the aggregate shall be
     initialized implicitly the same as objects that have static storage duration.

22   If an array of unknown size is initialized, its size is determined by the largest indexed
     element with an explicit initializer. The array type is completed at the end of its
     initializer list.
23   The evaluations of the initialization list expressions are indeterminately sequenced with
     respect to one another and thus the order in which any side effects occur is
     unspecified.152)
Footnote 152) In particular, the evaluation order need not be the same as the order of subobject initialization.
24   EXAMPLE 1        Provided that <complex.h> has been #included, the declarations
              int i = 3.5;
              double complex c = 5 + 3 * I;
     define and initialize i with the value 3 and c with the value 5. 0 + i 3. 0.

25   EXAMPLE 2        The declaration
              int x[] = { 1, 3, 5 };
     defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
     and there are three initializers.

26   EXAMPLE 3        The declaration
              int y[4][3] =          {
                    { 1, 3,          5 },
                    { 2, 4,          6 },
                    { 3, 5,          7 },
              };
     is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
     y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
     y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
     been achieved by
              int y[4][3] = {
                    1, 3, 5, 2, 4, 6, 3, 5, 7
              };
     The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
     next three are taken successively for y[1] and y[2].

27   EXAMPLE 4        The declaration
              int z[4][3] = {
                    { 1 }, { 2 }, { 3 }, { 4 }
              };
     initializes the first column of z as specified and initializes the rest with zeros.

28   EXAMPLE 5        The declaration
              struct { int a[3], b; } w[] = { { 1 }, 2 };
     is a definition with an inconsistently bracketed initialization. It defines an array with two element

     structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.

29   EXAMPLE 6         The declaration
               short q[4][3][2] = {
                     { 1 },
                     { 2, 3 },
                     { 4, 5, 6 }
               };
     contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
     object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
     q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
     q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
     only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
     for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
     respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
     diagnostic message would have been issued. The same initialization result could have been achieved by:
               short q[4][3][2] = {
                     1, 0, 0, 0, 0, 0,
                     2, 3, 0, 0, 0, 0,
                     4, 5, 6
               };
     or by:
               short q[4][3][2] = {
                     {
                           { 1 },
                     },
                     {
                           { 2, 3 },
                     },
                     {
                           { 4, 5 },
                           { 6 },
                     }
               };
     in a fully bracketed form.
30   Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
     cause confusion.

31   EXAMPLE 7         One form of initialization that completes array types involves typedef names. Given the
     declaration
               typedef int A[];            // OK - declared with block scope
     the declaration
               A a = { 1, 2 }, b = { 3, 4, 5 };
     is identical to
               int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
     due to the rules for incomplete types.

32   EXAMPLE 8       The declaration
              char s[] = "abc", t[3] = "abc";
     defines ``plain'' char array objects s and t whose elements are initialized with character string literals.
     This declaration is identical to
              char s[] = { 'a', 'b', 'c', '\0' },
                   t[] = { 'a', 'b', 'c' };
     The contents of the arrays are modifiable. On the other hand, the declaration
              char *p = "abc";
     defines p with type ``pointer to char'' and initializes it to point to an object with type ``array of char''
     with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
     modify the contents of the array, the behavior is undefined.

33   EXAMPLE 9       Arrays can be initialized to correspond to the elements of an enumeration by using
     designators:
              enum { member_one,           member_two };
              const char *nm[] =           {
                    [member_two]           = "member two",
                    [member_one]           = "member one",
              };

34   EXAMPLE 10       Structure members can be initialized to nonzero values without depending on their order:
              div_t answer = { .quot = 2, .rem = -1 };

35   EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
     might be misunderstood:
              struct { int a[3], b; } w[] =
                    { [0].a = {1}, [1].a[0] = 2 };

36   EXAMPLE 12       Space can be ``allocated'' from both ends of an array by using a single designator:
              int a[MAX] = {
                    1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
              };
37   In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
     than ten, some of the values provided by the first five initializers will be overridden by the second five.

38   EXAMPLE 13       Any member of a union can be initialized:
              union { /* ... */ } u = { .any_member = 42 };

     Forward references: common definitions <stddef.h> (7.19).

6.7.10 [Static assertions]


1            static_assert-declaration:
                     _Static_assert ( constant-expression , string-literal ) ;
    Constraints
2   The constant expression shall compare unequal to 0.
    Semantics
3   The constant expression shall be an integer constant expression. If the value of the
    constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
    constraint is violated and the implementation shall produce a diagnostic message that
    includes the text of the string literal, except that characters not in the basic source
    character set are not required to appear in the message.
    Forward references: diagnostics (7.2).

6.8 [Statements and blocks]


1            statement:
                    labeled-statement
                    compound-statement
                    expression-statement
                    selection-statement
                    iteration-statement
                    jump-statement
    Semantics
2   A statement specifies an action to be performed. Except as indicated, statements are
    executed in sequence.
3   A block allows a set of declarations and statements to be grouped into one syntactic unit.
    The initializers of objects that have automatic storage duration, and the variable length
    array declarators of ordinary identifiers with block scope, are evaluated and the values are
    stored in the objects (including storing an indeterminate value in objects without an
    initializer) each time the declaration is reached in the order of execution, as if it were a
    statement, and within each declaration in the order that declarators appear.
4   A full expression is an expression that is not part of another expression or of a declarator.
    Each of the following is a full expression: an initializer that is not part of a compound
    literal; the expression in an expression statement; the controlling expression of a selection
    statement (if or switch); the controlling expression of a while or do statement; each
    of the (optional) expressions of a for statement; the (optional) expression in a return
    statement. There is a sequence point between the evaluation of a full expression and the
    evaluation of the next full expression to be evaluated.
    Forward references: expression and null statements (6.8.3), selection statements
    (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).

6.8.1 [Labeled statements]


1            labeled-statement:
                    identifier : statement
                    case constant-expression : statement
                    default : statement
    Constraints
2   A case or default label shall appear only in a switch statement. Further
    constraints on such labels are discussed under the switch statement.

3   Label names shall be unique within a function.
    Semantics
4   Any statement may be preceded by a prefix that declares an identifier as a label name.
    Labels in themselves do not alter the flow of control, which continues unimpeded across
    them.
    Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).

6.8.2 [Compound statement]


1            compound-statement:
                   { block-item-listopt }
             block-item-list:
                     block-item
                     block-item-list block-item
             block-item:
                     declaration
                     statement
    Semantics
2   A compound statement is a block.

6.8.3 [Expression and null statements]


1            expression-statement:
                    expressionopt ;
    Semantics
2   The expression in an expression statement is evaluated as a void expression for its side
    effects.153)
Footnote 153) Such as assignments, and function calls which have side effects.
3   A null statement (consisting of just a semicolon) performs no operations.
4   EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
    discarding of its value may be made explicit by converting the expression to a void expression by means of
    a cast:
             int p(int);
             /* ... */
             (void)p(0);

5   EXAMPLE 2       In the program fragment
             char *s;
             /* ... */
             while (*s++ != '\0')
                     ;
    a null statement is used to supply an empty loop body to the iteration statement.

6   EXAMPLE 3       A null statement may also be used to carry a label just before the closing } of a compound
    statement.
             while (loop1) {
                   /* ... */
                   while (loop2) {
                           /* ... */
                           if (want_out)
                                   goto end_loop1;
                           /* ... */
                   }
                   /* ... */
             end_loop1: ;
             }

    Forward references: iteration statements (6.8.5).

6.8.4 [Selection statements]


1            selection-statement:
                     if ( expression ) statement
                     if ( expression ) statement else statement
                     switch ( expression ) statement
    Semantics
2   A selection statement selects among a set of statements depending on the value of a
    controlling expression.
3   A selection statement is a block whose scope is a strict subset of the scope of its
    enclosing block. Each associated substatement is also a block whose scope is a strict
    subset of the scope of the selection statement.

6.8.4.1 [The if statement]


1   The controlling expression of an if statement shall have scalar type.
    Semantics
2   In both forms, the first substatement is executed if the expression compares unequal to 0.
    In the else form, the second substatement is executed if the expression compares equal
    to 0. If the first substatement is reached via a label, the second substatement is not
    executed.
3   An else is associated with the lexically nearest preceding if that is allowed by the
    syntax.

6.8.4.2 [The switch statement]


1   The controlling expression of a switch statement shall have integer type.
2   If a switch statement has an associated case or default label within the scope of an
    identifier with a variably modified type, the entire switch statement shall be within the
    scope of that identifier.154)
Footnote 154) That is, the declaration either precedes the switch statement, or it follows the last case or
         default label associated with the switch that is in the block containing the declaration.
3   The expression of each case label shall be an integer constant expression and no two of
    the case constant expressions in the same switch statement shall have the same value
    after conversion. There may be at most one default label in a switch statement.
    (Any enclosed switch statement may have a default label or case constant
    expressions with values that duplicate case constant expressions in the enclosing
    switch statement.)
    Semantics
4   A switch statement causes control to jump to, into, or past the statement that is the
    switch body , depending on the value of a controlling expression, and on the presence of a
    default label and the values of any case labels on or in the switch body. A case or
    default label is accessible only within the closest enclosing switch statement.
5   The integer promotions are performed on the controlling expression. The constant
    expression in each case label is converted to the promoted type of the controlling
    expression. If a converted value matches that of the promoted controlling expression,
    control jumps to the statement following the matched case label. Otherwise, if there is
    a default label, control jumps to the labeled statement. If no converted case constant
    expression matches and there is no default label, no part of the switch body is
    executed.
    Implementation limits
6   As discussed in 5.2.4.1, the implementation may limit the number of case values in a
    switch statement.

7   EXAMPLE        In the artificial program fragment
             switch (expr)
             {
                   int i = 4;
                   f(i);
             case 0:
                   i = 17;
                   /* falls through into default code */
             default:
                   printf("%d\n", i);
             }
    the object whose identifier is i exists with automatic storage duration (within the block) but is never
    initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
    access an indeterminate value. Similarly, the call to the function f cannot be reached.


6.8.5 [Iteration statements]


1            iteration-statement:
                     while ( expression ) statement
                     do statement while ( expression ) ;
                     for ( expressionopt ; expressionopt ; expressionopt ) statement
                     for ( declaration expressionopt ; expressionopt ) statement
    Constraints
2   The controlling expression of an iteration statement shall have scalar type.
3   The declaration part of a for statement shall only declare identifiers for objects having
    storage class auto or register.
    Semantics
4   An iteration statement causes a statement called the loop body to be executed repeatedly
    until the controlling expression compares equal to 0. The repetition occurs regardless of
    whether the loop body is entered from the iteration statement or by a jump.155)
Footnote 155) Code jumped over is not executed. In particular, the controlling expression of a for or while
         statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
5   An iteration statement is a block whose scope is a strict subset of the scope of its
    enclosing block. The loop body is also a block whose scope is a strict subset of the scope
    of the iteration statement.
6   An iteration statement whose controlling expression is not a constant expression,156) that
    performs no input/output operations, does not access volatile objects, and performs no
    synchronization or atomic operations in its body, controlling expression, or (in the case of

    a for statement) its expression-3, may be assumed by the implementation to
    terminate.157)
Footnote 156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.
Footnote 157) This is intended to allow compiler transformations such as removal of empty loops even when
         termination cannot be proven.

6.8.5.1 [The while statement]


1   The evaluation of the controlling expression takes place before each execution of the loop
    body.

6.8.5.2 [The do statement]


1   The evaluation of the controlling expression takes place after each execution of the loop
    body.

6.8.5.3 [The for statement]


1   The statement
             for ( clause-1 ; expression-2 ; expression-3 ) statement
    behaves as follows: The expression expression-2 is the controlling expression that is
    evaluated before each execution of the loop body. The expression expression-3 is
    evaluated as a void expression after each execution of the loop body. If clause-1 is a
    declaration, the scope of any identifiers it declares is the remainder of the declaration and
    the entire loop, including the other two expressions; it is reached in the order of execution
    before the first evaluation of the controlling expression. If clause-1 is an expression, it is
    evaluated as a void expression before the first evaluation of the controlling expression.158)
Footnote 158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
         the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
         such that execution of the loop continues until the expression compares equal to 0; and expression-3
         specifies an operation (such as incrementing) that is performed after each iteration.
2   Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
    nonzero constant.

6.8.6 [Jump statements]


1            jump-statement:
                    goto identifier ;
                    continue ;
                    break ;
                    return expressionopt ;

    Semantics
2   A jump statement causes an unconditional jump to another place.

6.8.6.1 [The goto statement]


1   The identifier in a goto statement shall name a label located somewhere in the enclosing
    function. A goto statement shall not jump from outside the scope of an identifier having
    a variably modified type to inside the scope of that identifier.
    Semantics
2   A goto statement causes an unconditional jump to the statement prefixed by the named
    label in the enclosing function.
3   EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
    following outline presents one possible approach to a problem based on these three assumptions:
      1.   The general initialization code accesses objects only visible to the current function.
      2.   The general initialization code is too large to warrant duplication.
      3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
         continue statements, for example.)
            /* ... */
            goto first_time;
            for (;;) {
                    // determine next operation
                    /* ... */
                    if (need to reinitialize) {
                            // reinitialize-only code
                            /* ... */
                    first_time:
                            // general initialization code
                            /* ... */
                            continue;
                    }
                    // handle other operations
                    /* ... */
            }
4   EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
    modified types. A jump within the scope, however, is permitted.
            goto lab3;                         // invalid: going INTO scope of VLA.
            {
                  double a[n];
                  a[j] = 4.4;
            lab3:
                  a[j] = 3.3;
                  goto lab4;                   // valid: going WITHIN scope of VLA.
                  a[j] = 5.5;
            lab4:
                  a[j] = 6.6;
            }
            goto lab4;                         // invalid: going INTO scope of VLA.


6.8.6.2 [The continue statement]


1   A continue statement shall appear only in or as a loop body.
    Semantics
2   A continue statement causes a jump to the loop-continuation portion of the smallest
    enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
    of the statements
    while (/* ... */) {                  do {                                 for (/* ... */) {
       /* ... */                            /* ... */                            /* ... */
       continue;                            continue;                            continue;
       /* ... */                            /* ... */                            /* ... */
    contin: ;                            contin: ;                            contin: ;
    }                                    } while (/* ... */);                 }
    unless the continue statement shown is in an enclosed iteration statement (in which
    case it is interpreted within that statement), it is equivalent to goto contin;.159)
Footnote 159) Following the contin: label is a null statement.

6.8.6.3 [The break statement]


1   A break statement shall appear only in or as a switch body or loop body.
    Semantics
2   A break statement terminates execution of the smallest enclosing switch or iteration
    statement.


6.8.6.4 [The return statement]


1   A return statement with an expression shall not appear in a function whose return type
    is void. A return statement without an expression shall only appear in a function
    whose return type is void.
    Semantics
2   A return statement terminates execution of the current function and returns control to
    its caller. A function may have any number of return statements.
3   If a return statement with an expression is executed, the value of the expression is
    returned to the caller as the value of the function call expression. If the expression has a
    type different from the return type of the function in which it appears, the value is
    converted as if by assignment to an object having the return type of the function.160)
Footnote 160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
         apply to the case of function return. The representation of floating-point values may have wider range
         or precision than implied by the type; a cast may be used to remove this extra range and precision.
4   EXAMPLE       In:
            struct s { double i; } f(void);
            union {
                  struct {
                        int f1;
                        struct s f2;
                  } u1;
                  struct {
                        struct s f3;
                        int f4;
                  } u2;
            } g;
            struct s f(void)
            {
                  return g.u1.f2;
            }
            /* ... */
            g.u2.f3 = f();
    there is no undefined behavior, although there would be if the assignment were done directly (without using
    a function call to fetch the value).


6.9 [External definitions]


1            translation-unit:
                     external-declaration
                     translation-unit external-declaration
             external-declaration:
                    function-definition
                    declaration
    Constraints
2   The storage-class specifiers auto and register shall not appear in the declaration
    specifiers in an external declaration.
3   There shall be no more than one external definition for each identifier declared with
    internal linkage in a translation unit. Moreover, if an identifier declared with internal
    linkage is used in an expression (other than as a part of the operand of a sizeof or
    _Alignof operator whose result is an integer constant), there shall be exactly one
    external definition for the identifier in the translation unit.
    Semantics
4   As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
    which consists of a sequence of external declarations. These are described as ``external''
    because they appear outside any function (and hence have file scope). As discussed in
     6.7, a declaration that also causes storage to be reserved for an object or a function named
    by the identifier is a definition.
5   An external definition is an external declaration that is also a definition of a function
    (other than an inline definition) or an object. If an identifier declared with external
    linkage is used in an expression (other than as part of the operand of a sizeof or
    _Alignof operator whose result is an integer constant), somewhere in the entire
    program there shall be exactly one external definition for the identifier; otherwise, there
    shall be no more than one.161)

Footnote 161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
         external definition for it.

6.9.1 [Function definitions]


1            function-definition:
                    declaration-specifiers declarator declaration-listopt compound-statement
             declaration-list:
                    declaration
                    declaration-list declaration
    Constraints
2   The identifier declared in a function definition (which is the name of the function) shall
    have a function type, as specified by the declarator portion of the function definition.162)
Footnote 162) The intent is that the type category in a function definition cannot be inherited from a typedef:
                  typedef int F(void);                          //   type F is ``function with no parameters
                                                                //                  returning int''
                  F f, g;                                       //   f and g both have type compatible with F
                  F f { /* ... */ }                             //   WRONG: syntax/constraint error
                  F g() { /* ... */ }                           //   WRONG: declares that g returns a function
                  int f(void) { /* ... */ }                     //   RIGHT: f has type compatible with F
                  int g() { /* ... */ }                         //   RIGHT: g has type compatible with F
                  F *e(void) { /* ... */ }                      //   e returns a pointer to a function
                  F *((e))(void) { /* ... */ }                  //   same: parentheses irrelevant
                  int (*fp)(void);                              //   fp points to a function that has type F
                  F *Fp;                                        //   Fp points to a function that has type F
3   The return type of a function shall be void or a complete object type other than array
    type.
4   The storage-class specifier, if any, in the declaration specifiers shall be either extern or
    static.
5   If the declarator includes a parameter type list, the declaration of each parameter shall
    include an identifier, except for the special case of a parameter list consisting of a single
    parameter of type void, in which case there shall not be an identifier. No declaration list
    shall follow.
6   If the declarator includes an identifier list, each declaration in the declaration list shall
    have at least one declarator, those declarators shall declare only identifiers from the
    identifier list, and every identifier in the identifier list shall be declared. An identifier
    declared as a typedef name shall not be redeclared as a parameter. The declarations in the
    declaration list shall contain no storage-class specifier other than register and no
    initializations.
     Semantics
7    The declarator in a function definition specifies the name of the function being defined
     and the identifiers of its parameters. If the declarator includes a parameter type list, the
     list also specifies the types of all the parameters; such a declarator also serves as a
     function prototype for later calls to the same function in the same translation unit. If the
     declarator includes an identifier list,163) the types of the parameters shall be declared in a
     following declaration list. In either case, the type of each parameter is adjusted as
     described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
     type.
Footnote 163) See ``future language directions'' (6.11.7).
8    If a function that accepts a variable number of arguments is defined without a parameter
     type list that ends with the ellipsis notation, the behavior is undefined.
9    Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout
     of the storage for parameters is unspecified.
Footnote 164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.
10   On entry to the function, the size expressions of each variably modified parameter are
     evaluated and the value of each argument expression is converted to the type of the
     corresponding parameter as if by assignment. (Array expressions and function
     designators as arguments were converted to pointers before the call.)
11   After all parameters have been assigned, the compound statement that constitutes the
     body of the function definition is executed.
12   If the } that terminates a function is reached, and the value of the function call is used by
     the caller, the behavior is undefined.
13   EXAMPLE 1       In the following:
              extern int max(int a, int b)
              {
                    return a > b ? a : b;
              }
     extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
     function declarator; and
              { return a > b ? a : b; }
     is the function body. The following similar definition uses the identifier-list form for the parameter
     declarations:

              extern int max(a, b)
              int a, b;
              {
                    return a > b ? a : b;
              }
     Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
     that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
     to the function, whereas the second form does not.

14   EXAMPLE 2           To pass one function to another, one might say
                          int f(void);
                          /* ... */
                          g(f);
     Then the definition of g might read
              void g(int (*funcp)(void))
              {
                    /* ... */
                    (*funcp)(); /* or funcp(); ...                    */
              }
     or, equivalently,
              void g(int func(void))
              {
                    /* ... */
                    func(); /* or (*func)(); ...                   */
              }

6.9.2 [External object definitions]


1    If the declaration of an identifier for an object has file scope and an initializer, the
     declaration is an external definition for the identifier.
2    A declaration of an identifier for an object that has file scope without an initializer, and
     without a storage-class specifier or with the storage-class specifier static, constitutes a
     tentative definition. If a translation unit contains one or more tentative definitions for an
     identifier, and the translation unit contains no external definition for that identifier, then
     the behavior is exactly as if the translation unit contains a file scope declaration of that
     identifier, with the composite type as of the end of the translation unit, with an initializer
     equal to 0.
3    If the declaration of an identifier for an object is a tentative definition and has internal
     linkage, the declared type shall not be an incomplete type.
4   EXAMPLE 1
             int i1 = 1;                    // definition, external linkage
             static int i2 = 2;             // definition, internal linkage
             extern int i3 = 3;             // definition, external linkage
             int i4;                        // tentative definition, external linkage
             static int i5;                 // tentative definition, internal linkage
             int   i1;                      // valid tentative definition, refers to previous
             int   i2;                      // 6.2.2 renders undefined, linkage disagreement
             int   i3;                      // valid tentative definition, refers to previous
             int   i4;                      // valid tentative definition, refers to previous
             int   i5;                      // 6.2.2 renders undefined, linkage disagreement
             extern    int   i1;            // refers to previous, whose linkage is external
             extern    int   i2;            // refers to previous, whose linkage is internal
             extern    int   i3;            // refers to previous, whose linkage is external
             extern    int   i4;            // refers to previous, whose linkage is external
             extern    int   i5;            // refers to previous, whose linkage is internal

5   EXAMPLE 2       If at the end of the translation unit containing
             int i[];
    the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
    zero on program startup.

6.10 [Preprocessing directives]


1            preprocessing-file:
                    groupopt
             group:
                      group-part
                      group group-part
             group-part:
                    if-section
                    control-line
                    text-line
                    # non-directive
             if-section:
                      if-group elif-groupsopt else-groupopt endif-line
             if-group:
                     # if     constant-expression new-line groupopt
                     # ifdef identifier new-line groupopt
                     # ifndef identifier new-line groupopt
             elif-groups:
                     elif-group
                     elif-groups elif-group
             elif-group:
                     # elif         constant-expression new-line groupopt
             else-group:
                     # else         new-line groupopt
             endif-line:
                     # endif        new-line
             control-line:
                    # include pp-tokens new-line
                    # define identifier replacement-list new-line
                    # define identifier lparen identifier-listopt )
                                                    replacement-list new-line
                    # define identifier lparen ... ) replacement-list new-line
                    # define identifier lparen identifier-list , ... )
                                                    replacement-list new-line
                    # undef   identifier new-line
                    # line    pp-tokens new-line
                    # error   pp-tokensopt new-line
                    # pragma pp-tokensopt new-line
                    #         new-line
             text-line:
                     pp-tokensopt new-line
             non-directive:
                    pp-tokens new-line
             lparen:
                       a ( character not immediately preceded by white-space
             replacement-list:
                    pp-tokensopt
             pp-tokens:
                    preprocessing-token
                    pp-tokens preprocessing-token
             new-line:
                    the new-line character
    Description
2   A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
    following constraints: The first token in the sequence is a # preprocessing token that (at
    the start of translation phase 4) is either the first character in the source file (optionally
    after white space containing no new-line characters) or that follows white space
    containing at least one new-line character. The last token in the sequence is the first new-
    line character that follows the first token in the sequence.165) A new-line character ends
    the preprocessing directive even if it occurs within what would otherwise be an

    invocation of a function-like macro.
3   A text line shall not begin with a # preprocessing token. A non-directive shall not begin
    with any of the directive names appearing in the syntax.
4   When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
    sequence of preprocessing tokens to occur between the directive name and the following
    new-line character.
    Constraints
5   The only white-space characters that shall appear between preprocessing tokens within a
    preprocessing directive (from just after the introducing # preprocessing token through
    just before the terminating new-line character) are space and horizontal-tab (including
    spaces that have replaced comments or possibly other white-space characters in
    translation phase 3).
    Semantics
6   The implementation can process and skip sections of source files conditionally, include
    other source files, and replace macros. These capabilities are called preprocessing,
    because conceptually they occur before translation of the resulting translation unit.
7   The preprocessing tokens within a preprocessing directive are not subject to macro
    expansion unless otherwise stated.
8   EXAMPLE        In:
             #define EMPTY
             EMPTY # include <file.h>
    the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
    begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
    replaced.


6.10.1 [Conditional inclusion]


1   The expression that controls conditional inclusion shall be an integer constant expression
    except that: identifiers (including those lexically identical to keywords) are interpreted as
    described below;166) and it may contain unary operator expressions of the form
         defined identifier
    or
         defined ( identifier )
    which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is

    predefined or if it has been the subject of a #define preprocessing directive without an
    intervening #undef directive with the same subject identifier), 0 if it is not.
Footnote 166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
         either are or are not macro names -- there simply are no keywords, enumeration constants, etc.
2   Each preprocessing token that remains (in the list of preprocessing tokens that will
    become the controlling expression) after all macro replacements have occurred shall be in
    the lexical form of a token (6.4).
    Semantics
3   Preprocessing directives of the forms
       # if   constant-expression new-line groupopt
       # elif constant-expression new-line groupopt
    check whether the controlling constant expression evaluates to nonzero.
4   Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
    the controlling constant expression are replaced (except for those macro names modified
    by the defined unary operator), just as in normal text. If the token defined is
    generated as a result of this replacement process or use of the defined unary operator
    does not match one of the two specified forms prior to macro replacement, the behavior is
    undefined. After all replacements due to macro expansion and the defined unary
    operator have been performed, all remaining identifiers (including those lexically
    identical to keywords) are replaced with the pp-number 0, and then each preprocessing
    token is converted into a token. The resulting tokens compose the controlling constant
    expression which is evaluated according to the rules of 6.6. For the purposes of this
    token conversion and evaluation, all signed integer types and all unsigned integer types
    act as if they have the same representation as, respectively, the types intmax_t and
    uintmax_t defined in the header <stdint.h>.167) This includes interpreting
    character constants, which may involve converting escape sequences into execution
    character set members. Whether the numeric value for these character constants matches
    the value obtained when an identical character constant occurs in an expression (other
    than within a #if or #elif directive) is implementation-defined.168) Also, whether a
    single-character character constant may have a negative value is implementation-defined.
Footnote 167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
         0x8000 is signed and positive within a #if expression even though it would be unsigned in
         translation phase 7.
Footnote 168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
         evaluate to the same value in these two contexts.
            #if 'z' - 'a' == 25
            if ('z' - 'a' == 25)
5   Preprocessing directives of the forms
       # ifdef identifier new-line groupopt
       # ifndef identifier new-line groupopt
    check whether the identifier is or is not currently defined as a macro name. Their
    conditions are equivalent to #if defined identifier and #if !defined identifier
    respectively.
6   Each directive's condition is checked in order. If it evaluates to false (zero), the group
    that it controls is skipped: directives are processed only through the name that determines
    the directive in order to keep track of the level of nested conditionals; the rest of the
    directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
    group. Only the first group whose control condition evaluates to true (nonzero) is
    processed. If none of the conditions evaluates to true, and there is a #else directive, the
    group controlled by the #else is processed; lacking a #else directive, all the groups
    until the #endif are skipped.169)
    Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
    integer types (7.20.1.5).
Footnote 169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
         before the terminating new-line character. However, comments may appear anywhere in a source file,
         including within a preprocessing directive.

6.10.2 [Source file inclusion]


1   A #include directive shall identify a header or source file that can be processed by the
    implementation.
    Semantics
2   A preprocessing directive of the form
       # include <h-char-sequence> new-line
    searches a sequence of implementation-defined places for a header identified uniquely by
    the specified sequence between the < and > delimiters, and causes the replacement of that
    directive by the entire contents of the header. How the places are specified or the header
    identified is implementation-defined.
3   A preprocessing directive of the form
       # include "q-char-sequence" new-line
    causes the replacement of that directive by the entire contents of the source file identified
    by the specified sequence between the " delimiters. The named source file is searched

    for in an implementation-defined manner. If this search is not supported, or if the search
    fails, the directive is reprocessed as if it read
       # include <h-char-sequence> new-line
    with the identical contained sequence (including > characters, if any) from the original
    directive.
4   A preprocessing directive of the form
       # include pp-tokens new-line
    (that does not match one of the two previous forms) is permitted. The preprocessing
    tokens after include in the directive are processed just as in normal text. (Each
    identifier currently defined as a macro name is replaced by its replacement list of
    preprocessing tokens.) The directive resulting after all replacements shall match one of
    the two previous forms.170) The method by which a sequence of preprocessing tokens
    between a < and a > preprocessing token pair or a pair of " characters is combined into a
    single header name preprocessing token is implementation-defined.
Footnote 170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
         phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.
5   The implementation shall provide unique mappings for sequences consisting of one or
    more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
    first character shall not be a digit. The implementation may ignore distinctions of
    alphabetical case and restrict the mapping to eight significant characters before the
    period.
6   A #include preprocessing directive may appear in a source file that has been read
    because of a #include directive in another file, up to an implementation-defined
    nesting limit (see 5.2.4.1).
7   EXAMPLE 1       The most common uses of #include preprocessing directives are as in the following:
              #include <stdio.h>
              #include "myprog.h"

8   EXAMPLE 2     This illustrates macro-replaced #include directives:
           #if VERSION == 1
                 #define INCFILE            "vers1.h"
           #elif VERSION == 2
                 #define INCFILE            "vers2.h"        // and so on
           #else
                  #define INCFILE           "versN.h"
           #endif
           #include INCFILE

    Forward references: macro replacement (6.10.3).

6.10.3 [Macro replacement]


1   Two replacement lists are identical if and only if the preprocessing tokens in both have
    the same number, ordering, spelling, and white-space separation, where all white-space
    separations are considered identical.
2   An identifier currently defined as an object-like macro shall not be redefined by another
    #define preprocessing directive unless the second definition is an object-like macro
    definition and the two replacement lists are identical. Likewise, an identifier currently
    defined as a function-like macro shall not be redefined by another #define
    preprocessing directive unless the second definition is a function-like macro definition
    that has the same number and spelling of parameters, and the two replacement lists are
    identical.
3   There shall be white-space between the identifier and the replacement list in the definition
    of an object-like macro.
4   If the identifier-list in the macro definition does not end with an ellipsis, the number of
    arguments (including those arguments consisting of no preprocessing tokens) in an
    invocation of a function-like macro shall equal the number of parameters in the macro
    definition. Otherwise, there shall be more arguments in the invocation than there are
    parameters in the macro definition (excluding the ...). There shall exist a )
    preprocessing token that terminates the invocation.
5   The identifier _ _VA_ARGS_ _ shall occur only in the replacement-list of a function-like
    macro that uses the ellipsis notation in the parameters.
6   A parameter identifier in a function-like macro shall be uniquely declared within its
    scope.
    Semantics
7   The identifier immediately following the define is called the macro name. There is one
    name space for macro names. Any white-space characters preceding or following the
    replacement list of preprocessing tokens are not considered part of the replacement list

     for either form of macro.
8    If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
     a preprocessing directive could begin, the identifier is not subject to macro replacement.
9    A preprocessing directive of the form
        # define identifier replacement-list new-line
     defines an object-like macro that causes each subsequent instance of the macro name171)
     to be replaced by the replacement list of preprocessing tokens that constitute the
     remainder of the directive. The replacement list is then rescanned for more macro names
     as specified below.
Footnote 171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
          not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
          are never scanned for macro names or parameters.
10   A preprocessing directive of the form
        # define identifier lparen identifier-listopt ) replacement-list new-line
        # define identifier lparen ... ) replacement-list new-line
        # define identifier lparen identifier-list , ... ) replacement-list new-line
     defines a function-like macro with parameters, whose use is similar syntactically to a
     function call. The parameters are specified by the optional list of identifiers, whose scope
     extends from their declaration in the identifier list until the new-line character that
     terminates the #define preprocessing directive. Each subsequent instance of the
     function-like macro name followed by a ( as the next preprocessing token introduces the
     sequence of preprocessing tokens that is replaced by the replacement list in the definition
     (an invocation of the macro). The replaced sequence of preprocessing tokens is
     terminated by the matching ) preprocessing token, skipping intervening matched pairs of
     left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
     tokens making up an invocation of a function-like macro, new-line is considered a normal
     white-space character.
11   The sequence of preprocessing tokens bounded by the outside-most matching parentheses
     forms the list of arguments for the function-like macro. The individual arguments within
     the list are separated by comma preprocessing tokens, but comma preprocessing tokens
     between matching inner parentheses do not separate arguments. If there are sequences of
     preprocessing tokens within the list of arguments that would otherwise act as
     preprocessing directives,172) the behavior is undefined.
Footnote 172) Despite the name, a non-directive is a preprocessing directive.
12   If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
     including any separating comma preprocessing tokens, are merged to form a single item:

    the variable arguments. The number of arguments so combined is such that, following
    merger, the number of arguments is one more than the number of parameters in the macro
    definition (excluding the ...).

6.10.3.1 [Argument substitution]


1   After the arguments for the invocation of a function-like macro have been identified,
    argument substitution takes place. A parameter in the replacement list, unless preceded
    by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
    replaced by the corresponding argument after all macros contained therein have been
    expanded. Before being substituted, each argument's preprocessing tokens are
    completely macro replaced as if they formed the rest of the preprocessing file; no other
    preprocessing tokens are available.
2   An identifier _ _VA_ARGS_ _ that occurs in the replacement list shall be treated as if it
    were a parameter, and the variable arguments shall form the preprocessing tokens used to
    replace it.

6.10.3.2 [The # operator]


1   Each # preprocessing token in the replacement list for a function-like macro shall be
    followed by a parameter as the next preprocessing token in the replacement list.
    Semantics
2   If, in the replacement list, a parameter is immediately preceded by a # preprocessing
    token, both are replaced by a single character string literal preprocessing token that
    contains the spelling of the preprocessing token sequence for the corresponding
    argument. Each occurrence of white space between the argument's preprocessing tokens
    becomes a single space character in the character string literal. White space before the
    first preprocessing token and after the last preprocessing token composing the argument
    is deleted. Otherwise, the original spelling of each preprocessing token in the argument
    is retained in the character string literal, except for special handling for producing the
    spelling of string literals and character constants: a \ character is inserted before each "
    and \ character of a character constant or string literal (including the delimiting "
    characters), except that it is implementation-defined whether a \ character is inserted
    before the \ character beginning a universal character name. If the replacement that
    results is not a valid character string literal, the behavior is undefined. The character
    string literal corresponding to an empty argument is "". The order of evaluation of # and
    ## operators is unspecified.

6.10.3.3 [The ## operator]


1   A ## preprocessing token shall not occur at the beginning or at the end of a replacement
    list for either form of macro definition.
    Semantics
2   If, in the replacement list of a function-like macro, a parameter is immediately preceded
    or followed by a ## preprocessing token, the parameter is replaced by the corresponding
    argument's preprocessing token sequence; however, if an argument consists of no
    preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
    instead.173)
Footnote 173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
         exist only within translation phase 4.
3   For both object-like and function-like macro invocations, before the replacement list is
    reexamined for more macro names to replace, each instance of a ## preprocessing token
    in the replacement list (not from an argument) is deleted and the preceding preprocessing
    token is concatenated with the following preprocessing token. Placemarker
    preprocessing tokens are handled specially: concatenation of two placemarkers results in
    a single placemarker preprocessing token, and concatenation of a placemarker with a
    non-placemarker preprocessing token results in the non-placemarker preprocessing token.
    If the result is not a valid preprocessing token, the behavior is undefined. The resulting
    token is available for further macro replacement. The order of evaluation of ## operators
    is unspecified.
4   EXAMPLE       In the following fragment:
            #define     hash_hash # ## #
            #define     mkstr(a) # a
            #define     in_between(a) mkstr(a)
            #define     join(c, d) in_between(c hash_hash d)
            char p[] = join(x, y); // equivalent to
                                   // char p[] = "x ## y";
    The expansion produces, at various stages:
            join(x, y)
            in_between(x hash_hash y)
            in_between(x ## y)
            mkstr(x ## y)
            "x ## y"
    In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
    this new token is not the ## operator.


6.10.3.4 [Rescanning and further replacement]


1   After all parameters in the replacement list have been substituted and # and ##
    processing has taken place, all placemarker preprocessing tokens are removed. The
    resulting preprocessing token sequence is then rescanned, along with all subsequent
    preprocessing tokens of the source file, for more macro names to replace.
2   If the name of the macro being replaced is found during this scan of the replacement list
    (not including the rest of the source file's preprocessing tokens), it is not replaced.
    Furthermore, if any nested replacements encounter the name of the macro being replaced,
    it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
    available for further replacement even if they are later (re)examined in contexts in which
    that macro name preprocessing token would otherwise have been replaced.
3   The resulting completely macro-replaced preprocessing token sequence is not processed
    as a preprocessing directive even if it resembles one, but all pragma unary operator
    expressions within it are then processed as specified in 6.10.9 below.
4   EXAMPLE There are cases where it is not clear whether a replacement is nested or not. For example,
    given the following macro definitions:
            #define f(a) a*g
            #define g(a) f(a)
    the invocation
            f(2)(9)
    may expand to either
            2*f(9)
    or
            2*9*g
    Strictly conforming programs are not permitted to depend on such unspecified behavior.


6.10.3.5 [Scope of macro definitions]


1   A macro definition lasts (independent of block structure) until a corresponding #undef
    directive is encountered or (if none is encountered) until the end of the preprocessing
    translation unit. Macro definitions have no significance after translation phase 4.
2   A preprocessing directive of the form
         # undef identifier new-line
    causes the specified identifier no longer to be defined as a macro name. It is ignored if
    the specified identifier is not currently defined as a macro name.
3   EXAMPLE 1        The simplest use of this facility is to define a ``manifest constant'', as in
            #define TABSIZE 100
             int table[TABSIZE];

4   EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
    It has the advantages of working for any compatible types of the arguments and of generating in-line code
    without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
    arguments a second time (including side effects) and generating more code than a function if invoked
    several times. It also cannot have its address taken, as it has none.
             #define max(a, b) ((a) > (b) ? (a) : (b))
    The parentheses ensure that the arguments and the resulting expression are bound properly.

5   EXAMPLE 3      To illustrate the rules for redefinition and reexamination, the sequence
             #define    x          3
             #define    f(a)       f(x * (a))
             #undef     x
             #define    x          2
             #define    g          f
             #define    z          z[0]
             #define    h          g(~
             #define    m(a)       a(w)
             #define    w          0,1
             #define    t(a)       a
             #define    p()        int
             #define    q(x)       x
             #define    r(x,y)     x ## y
             #define    str(x)     # x
             f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
             g(x+(3,4)-w) | h 5) & m
                   (f)^m(m);
             p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
             char c[2][6] = { str(hello), str() };
    results in
             f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
             f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
             int i[] = { 1, 23, 4, 5, };
             char c[2][6] = { "hello", "" };

6   EXAMPLE 4      To illustrate the rules for creating character string literals and concatenating tokens, the
    sequence
             #define str(s)      # s
             #define xstr(s)     str(s)
             #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
                                     x ## s, x ## t)
             #define INCFILE(n) vers ## n
             #define glue(a, b) a ## b
             #define xglue(a, b) glue(a, b)
             #define HIGHLOW     "hello"
             #define LOW         LOW ", world"
             debug(1, 2);
             fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
                   == 0) str(: @\n), s);
             #include xstr(INCFILE(2).h)
             glue(HIGH, LOW);
             xglue(HIGH, LOW)
    results in
             printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
             fputs(
               "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
               s);
             #include "vers2.h"    (after macro replacement, before file access)
             "hello";
             "hello" ", world"
    or, after concatenation of the character string literals,
             printf("x1= %d, x2= %s", x1, x2);
             fputs(
               "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
               s);
             #include "vers2.h"    (after macro replacement, before file access)
             "hello";
             "hello, world"
    Space around the # and ## tokens in the macro definition is optional.

7   EXAMPLE 5        To illustrate the rules for placemarker preprocessing tokens, the sequence
             #define t(x,y,z) x ## y ## z
             int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
                        t(10,,), t(,11,), t(,,12), t(,,) };
    results in
             int j[] = { 123, 45, 67, 89,
                         10, 11, 12, };

8   EXAMPLE 6        To demonstrate the redefinition rules, the following sequence is valid.
             #define      OBJ_LIKE      (1-1)
             #define      OBJ_LIKE      /* white space */ (1-1) /* other */
             #define      FUNC_LIKE(a)   ( a )
             #define      FUNC_LIKE( a )( /* note the white space */ \
                                          a /* other stuff on this line
                                              */ )
    But the following redefinitions are invalid:
             #define      OBJ_LIKE    (0)     // different token sequence
             #define      OBJ_LIKE    (1 - 1) // different white space
             #define      FUNC_LIKE(b) ( a ) // different parameter usage
             #define      FUNC_LIKE(b) ( b ) // different parameter spelling

9   EXAMPLE 7        Finally, to show the variable argument list macro facilities:
             #define debug(...)       fprintf(stderr, _ _VA_ARGS_ _)
             #define showlist(...)    puts(#_ _VA_ARGS_ _)
             #define report(test, ...) ((test)?puts(#test):\
                         printf(_ _VA_ARGS_ _))
             debug("Flag");
             debug("X = %d\n", x);
             showlist(The first, second, and third items.);
             report(x>y, "x is %d but y is %d", x, y);
    results in
             fprintf(stderr, "Flag" );
             fprintf(stderr, "X = %d\n", x );
             puts( "The first, second, and third items." );
             ((x>y)?puts("x>y"):
                         printf("x is %d but y is %d", x, y));


6.10.4 [Line control]


1   The string literal of a #line directive, if present, shall be a character string literal.
    Semantics
2   The line number of the current source line is one greater than the number of new-line
    characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
    file to the current token.
3   A preprocessing directive of the form
       # line digit-sequence new-line
    causes the implementation to behave as if the following sequence of source lines begins
    with a source line that has a line number as specified by the digit sequence (interpreted as
    a decimal integer). The digit sequence shall not specify zero, nor a number greater than 2147483647.
4   A preprocessing directive of the form
       # line digit-sequence "s-char-sequenceopt" new-line
    sets the presumed line number similarly and changes the presumed name of the source
    file to be the contents of the character string literal.
5   A preprocessing directive of the form
       # line pp-tokens new-line
    (that does not match one of the two previous forms) is permitted. The preprocessing
    tokens after line on the directive are processed just as in normal text (each identifier
    currently defined as a macro name is replaced by its replacement list of preprocessing
    tokens). The directive resulting after all replacements shall match one of the two
    previous forms and is then processed as appropriate.

6.10.5 [Error directive]


1   A preprocessing directive of the form
       # error pp-tokensopt new-line
    causes the implementation to produce a diagnostic message that includes the specified
    sequence of preprocessing tokens.

6.10.6 [Pragma directive]


1   A preprocessing directive of the form
       # pragma pp-tokensopt new-line
    where the preprocessing token STDC does not immediately follow pragma in the
    directive (prior to any macro replacement)174) causes the implementation to behave in an
    implementation-defined manner. The behavior might cause translation to fail or cause the
    translator or the resulting program to behave in a non-conforming manner. Any such
    pragma that is not recognized by the implementation is ignored.
Footnote 174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
         except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
         replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
         implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
         but is not required to.
2   If the preprocessing token STDC does immediately follow pragma in the directive (prior
    to any macro replacement), then no macro replacement is performed on the directive, and
    the directive shall have one of the following forms175) whose meanings are described
    elsewhere:
       #pragma STDC FP_CONTRACT on-off-switch
       #pragma STDC FENV_ACCESS on-off-switch
       #pragma STDC CX_LIMITED_RANGE on-off-switch
       on-off-switch: one of
                   ON     OFF           DEFAULT
    Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
    (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).

Footnote 175) See ``future language directions'' (6.11.8).

6.10.7 [Null directive]


1   A preprocessing directive of the form
       # new-line
    has no effect.

6.10.8 [Predefined macro names]


1   The values of the predefined macros listed in the following subclauses176) (except for
    _ _FILE_ _ and _ _LINE_ _) remain constant throughout the translation unit.
Footnote 176) See ``future language directions'' (6.11.9).
2   None of these macro names, nor the identifier defined, shall be the subject of a
    #define or a #undef preprocessing directive. Any other predefined macro names
    shall begin with a leading underscore followed by an uppercase letter or a second
    underscore.
3   The implementation shall not predefine the macro _ _cplusplus, nor shall it define it
    in any standard header.
    Forward references: standard headers (7.1.2).

6.10.8.1 [Mandatory macros]


1   The following macro names shall be defined by the implementation:
    _ _DATE_ _ The date of translation of the preprocessing translation unit: a character
               string literal of the form "Mmm dd yyyy", where the names of the
               months are the same as those generated by the asctime function, and the
               first character of dd is a space character if the value is less than 10. If the
               date of translation is not available, an implementation-defined valid date
               shall be supplied.
    _ _FILE_ _ The presumed name of the current source file (a character string literal).177)
    _ _LINE_ _ The presumed line number (within the current source file) of the current
               source line (an integer constant).177)
    _ _STDC_ _ The integer constant 1, intended to indicate a conforming implementation.
    _ _STDC_HOSTED_ _ The integer constant 1 if the implementation is a hosted
              implementation or the integer constant 0 if it is not.

    _ _STDC_VERSION_ _ The integer constant 201ymmL.178)
    _ _TIME_ _ The time of translation of the preprocessing translation unit: a character
               string literal of the form "hh:mm:ss" as in the time generated by the
               asctime function. If the time of translation is not available, an
               implementation-defined valid time shall be supplied.
    Forward references: the asctime function (7.27.3.1).
Footnote 177) The presumed source file name and line number can be changed by the #line directive.
Footnote 177) The presumed source file name and line number can be changed by the #line directive.
Footnote 178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
         ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
         remain an integer constant of type long int that is increased with each revision of this International
         Standard.

6.10.8.2 [Environment macros]


1   The following macro names are conditionally defined by the implementation:
    _ _STDC_ISO_10646_ _ An integer constant of the form yyyymmL (for example,
              199712L). If this symbol is defined, then every character in the Unicode
              required set, when stored in an object of type wchar_t, has the same
              value as the short identifier of that character. The Unicode required set
              consists of all the characters that are defined by ISO/IEC 10646, along with
              all amendments and technical corrigenda, as of the specified year and
              month. If some other encoding is used, the macro shall not be defined and
              the actual encoding used is implementation-defined.
    _ _STDC_MB_MIGHT_NEQ_WC_ _ The integer constant 1, intended to indicate that, in
              the encoding for wchar_t, a member of the basic character set need not
              have a code value equal to its value when used as the lone character in an
              integer character constant.
    _ _STDC_UTF_16_ _ The integer constant 1, intended to indicate that values of type
              char16_t are UTF-16 encoded. If some other encoding is used, the
              macro shall not be defined and the actual encoding used is implementation-
              defined.
    _ _STDC_UTF_32_ _ The integer constant 1, intended to indicate that values of type
              char32_t are UTF-32 encoded. If some other encoding is used, the
              macro shall not be defined and the actual encoding used is implementation-
              defined.
    Forward references: common definitions (7.19), unicode utilities (7.28).


6.10.8.3 [Conditional feature macros]


1   The following macro names are conditionally defined by the implementation:
    _ _STDC_ANALYZABLE_ _ The integer constant 1, intended to indicate conformance to
              the specifications in annex L (Analyzability).
    _ _STDC_IEC_559_ _ The integer constant 1, intended to indicate conformance to the
              specifications in annex F (IEC 60559 floating-point arithmetic).
    _ _STDC_IEC_559_COMPLEX_ _ The integer constant 1, intended to indicate
              adherence to the specifications in annex G (IEC 60559 compatible complex
              arithmetic).
    _ _STDC_LIB_EXT1_ _ The integer constant 201ymmL, intended to indicate support
              for the extensions defined in annex K (Bounds-checking interfaces).179)
    _ _STDC_NO_ATOMICS_ _ The integer constant 1, intended to indicate that the
              implementation does not support atomic types (including the _Atomic
              type qualifier) and the <stdatomic.h> header.
    _ _STDC_NO_COMPLEX_ _ The integer constant 1, intended to indicate that the
              implementation does not support complex types or the <complex.h>
              header.
    _ _STDC_NO_THREADS_ _ The integer constant 1, intended to indicate that the
              implementation does not support the <threads.h> header.
    _ _STDC_NO_VLA_ _ The integer constant 1, intended to indicate that the
              implementation does not support variable length arrays or variably
              modified types.
Footnote 179) The intention is that this will remain an integer constant of type long int that is increased with
         each revision of this International Standard.
2   An implementation that defines _ _STDC_NO_COMPLEX_ _ shall not define
    _ _STDC_IEC_559_COMPLEX_ _.


6.10.9 [Pragma operator]


1   A unary operator expression of the form:
       _Pragma ( string-literal )
    is processed as follows: The string literal is destringized by deleting any encoding prefix,
    deleting the leading and trailing double-quotes, replacing each escape sequence \" by a
    double-quote, and replacing each escape sequence \\ by a single backslash. The
    resulting sequence of characters is processed through translation phase 3 to produce
    preprocessing tokens that are executed as if they were the pp-tokens in a pragma
    directive. The original four preprocessing tokens in the unary operator expression are
    removed.
2   EXAMPLE       A directive of the form:
             #pragma listing on "..\listing.dir"
    can also be expressed as:
             _Pragma ( "listing on \"..\\listing.dir\"" )
    The latter form is processed in the same way whether it appears literally as shown, or results from macro
    replacement, as in:
             #define LISTING(x) PRAGMA(listing on #x)
             #define PRAGMA(x) _Pragma(#x)
             LISTING ( ..\listing.dir )

6.11 [Future language directions]

 Future language directions

6.11.1 [Floating types]


1   Future standardization may include additional floating-point types, including those with
    greater range, precision, or both than long double.

6.11.2 [Linkages of identifiers]


1   Declaring an identifier with internal linkage at file scope without the static storage-
    class specifier is an obsolescent feature.

6.11.3 [External names]


1   Restriction of the significance of an external name to fewer than 255 characters
    (considering each universal character name or extended source character as a single
    character) is an obsolescent feature that is a concession to existing implementations.

6.11.4 [Character escape sequences]


1   Lowercase letters as escape sequences are reserved for future standardization. Other
    characters may be used in extensions.

6.11.5 [Storage-class specifiers]


1   The placement of a storage-class specifier other than at the beginning of the declaration
    specifiers in a declaration is an obsolescent feature.

6.11.6 [Function declarators]


1   The use of function declarators with empty parentheses (not prototype-format parameter
    type declarators) is an obsolescent feature.

6.11.7 [Function definitions]


1   The use of function definitions with separate parameter identifier and declaration lists
    (not prototype-format parameter type and identifier declarators) is an obsolescent feature.

6.11.8 [Pragma directives]


1   Pragmas whose first preprocessing token is STDC are reserved for future standardization.

6.11.9 [Predefined macro names]


1   Macro names beginning with _ _STDC_ are reserved for future standardization.


7. [Library]

 Library

7.1 [Introduction]

 Introduction

7.1.1 [Definitions of terms]


1   A string is a contiguous sequence of characters terminated by and including the first null
    character. The term multibyte string is sometimes used instead to emphasize special
    processing given to multibyte characters contained in the string or to avoid confusion
    with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
    character. The length of a string is the number of bytes preceding the null character and
    the value of a string is the sequence of the values of the contained characters, in order.
2   The decimal-point character is the character used by functions that convert floating-point
    numbers to or from character sequences to denote the beginning of the fractional part of
    such character sequences.180) It is represented in the text and examples by a period, but
    may be changed by the setlocale function.
Footnote 180) The functions that make use of the decimal-point character are the numeric conversion functions
         (7.22.1, 7.29.4.1) and the formatted input/output functions (7.21.6, 7.29.2).
3   A null wide character is a wide character with code value zero.
4   A wide string is a contiguous sequence of wide characters terminated by and including
    the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
    addressed) wide character. The length of a wide string is the number of wide characters
    preceding the null wide character and the value of a wide string is the sequence of code
    values of the contained wide characters, in order.
5   A shift sequence is a contiguous sequence of bytes within a multibyte string that
    (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
    corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
    character.181)
    Forward references: character handling (7.4), the setlocale function (7.11.1.1).

Footnote 181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
         enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
         sequence of maximum length. Whether these counts provide for more than one shift sequence is the
         implementation's choice.

7.1.2 [Standard headers]


1   Each library function is declared, with a type that includes a prototype, in a header ,182)
    whose contents are made available by the #include preprocessing directive. The
    header declares a set of related functions, plus any necessary types and additional macros
    needed to facilitate their use. Declarations of types described in this clause shall not
    include type qualifiers, unless explicitly stated otherwise.
Footnote 182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
         necessarily valid source file names.
2   The standard headers are183)
           <assert.h>                      <math.h>                        <stdlib.h>
           <complex.h>                     <setjmp.h>                      <stdnoreturn.h>
           <ctype.h>                       <signal.h>                      <string.h>
           <errno.h>                       <stdalign.h>                    <tgmath.h>
           <fenv.h>                        <stdarg.h>                      <threads.h>
           <float.h>                       <stdatomic.h>                   <time.h>
           <inttypes.h>                    <stdbool.h>                     <uchar.h>
           <iso646.h>                      <stddef.h>                      <wchar.h>
           <limits.h>                      <stdint.h>                      <wctype.h>
           <locale.h>                      <stdio.h>
Footnote 183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
         implementations need not support; see 6.10.8.3.
3   If a file with the same name as one of the above < and > delimited sequences, not
    provided as part of the implementation, is placed in any of the standard places that are
    searched for included source files, the behavior is undefined.
4   Standard headers may be included in any order; each may be included more than once in
    a given scope, with no effect different from being included only once, except that the
    effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
    used, a header shall be included outside of any external declaration or definition, and it
    shall first be included before the first reference to any of the functions or objects it
    declares, or to any of the types or macros it defines. However, if an identifier is declared
    or defined in more than one header, the second and subsequent associated headers may be
    included after the initial reference to the identifier. The program shall not have any
    macros with names lexically identical to keywords currently defined prior to the inclusion
    of the header or when any macro defined in the header is expanded.
5   Any definition of an object-like macro described in this clause shall expand to code that is
    fully protected by parentheses where necessary, so that it groups in an arbitrary
    expression as if it were a single identifier.

6   Any declaration of a library function shall have external linkage.
7   A summary of the contents of the standard headers is given in annex B.
    Forward references: diagnostics (7.2).

7.1.3 [Reserved identifiers]


1   Each header declares or defines all identifiers listed in its associated subclause, and
    optionally declares or defines identifiers listed in its associated future library directions
    subclause and identifiers which are always reserved either for any use or for use as file
    scope identifiers.
    -- All identifiers that begin with an underscore and either an uppercase letter or another
       underscore are always reserved for any use.
    -- All identifiers that begin with an underscore are always reserved for use as identifiers
       with file scope in both the ordinary and tag name spaces.
    -- Each macro name in any of the following subclauses (including the future library
       directions) is reserved for use as specified if any of its associated headers is included;
       unless explicitly stated otherwise (see 7.1.4).
    -- All identifiers with external linkage in any of the following subclauses (including the
       future library directions) and errno are always reserved for use as identifiers with
       external linkage.184)
    -- Each identifier with file scope listed in any of the following subclauses (including the
       future library directions) is reserved for use as a macro name and as an identifier with
       file scope in the same name space if any of its associated headers is included.
Footnote 184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
         va_copy, and va_end.
2   No other identifiers are reserved. If the program declares or defines an identifier in a
    context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
    identifier as a macro name, the behavior is undefined.
3   If the program removes (with #undef) any macro definition of an identifier in the first
    group listed above, the behavior is undefined.


7.1.4 [Use of library functions]


1   Each of the following statements applies unless explicitly stated otherwise in the detailed
    descriptions that follow: If an argument to a function has an invalid value (such as a value
    outside the domain of the function, or a pointer outside the address space of the program,
    or a null pointer, or a pointer to non-modifiable storage when the corresponding
    parameter is not const-qualified) or a type (after promotion) not expected by a function
    with variable number of arguments, the behavior is undefined. If a function argument is
    described as being an array, the pointer actually passed to the function shall have a value
    such that all address computations and accesses to objects (that would be valid if the
    pointer did point to the first element of such an array) are in fact valid. Any function
    declared in a header may be additionally implemented as a function-like macro defined in
    the header, so if a library function is declared explicitly when its header is included, one
    of the techniques shown below can be used to ensure the declaration is not affected by
    such a macro. Any macro definition of a function can be suppressed locally by enclosing
    the name of the function in parentheses, because the name is then not followed by the left
    parenthesis that indicates expansion of a macro function name. For the same syntactic
    reason, it is permitted to take the address of a library function even if it is also defined as
    a macro.185) The use of #undef to remove any macro definition will also ensure that an
    actual function is referred to. Any invocation of a library function that is implemented as
    a macro shall expand to code that evaluates each of its arguments exactly once, fully
    protected by parentheses where necessary, so it is generally safe to use arbitrary
    expressions as arguments.186) Likewise, those function-like macros described in the
    following subclauses may be invoked in an expression anywhere a function with a
    compatible return type could be called.187) All object-like macros listed as expanding to

    integer constant expressions shall additionally be suitable for use in #if preprocessing
    directives.
Footnote 185) This means that an implementation shall provide an actual function for each library function, even if it
         also provides a macro for that function.
Footnote 186) Such macros might not contain the sequence points that the corresponding function calls do.
Footnote 187) Because external identifiers and some macro names beginning with an underscore are reserved,
         implementations may provide special semantics for such names. For example, the identifier
         _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
         appropriate header could specify
                  #define abs(x) _BUILTIN_abs(x)
         for a compiler whose code generator will accept it.
         In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
         function may write
                  #undef abs
         whether the implementation's header provides a macro implementation of abs or a built-in
         implementation. The prototype for the function, which precedes and is hidden by any macro
         definition, is thereby revealed also.
2   Provided that a library function can be declared without reference to any type defined in a
    header, it is also permissible to declare the function and use it without including its
    associated header.
3   There is a sequence point immediately before a library function returns.
4   The functions in the standard library are not guaranteed to be reentrant and may modify
    objects with static or thread storage duration.188)
Footnote 188) Thus, a signal handler cannot, in general, call standard library functions.
5   Unless explicitly stated otherwise in the detailed descriptions that follow, library
    functions shall prevent data races as follows: A library function shall not directly or
    indirectly access objects accessible by threads other than the current thread unless the
    objects are accessed directly or indirectly via the function's arguments. A library
    function shall not directly or indirectly modify objects accessible by threads other than
    the current thread unless the objects are accessed directly or indirectly via the function's
    non-const arguments.189) Implementations may share their own internal objects between
    threads if the objects are not visible to users and are protected against data races.
Footnote 189) This means, for example, that an implementation is not permitted to use a static object for internal
         purposes without synchronization because it could cause a data race even in programs that do not
         explicitly share objects between threads. Similarly, an implementation of memcpy is not permitted to
         copy bytes beyond the specified length of the destination object and then restore the original values
         because it could cause a data race if the program shared those bytes between threads.
6   Unless otherwise specified, library functions shall perform all operations solely within the
    current thread if those operations have effects that are visible to users.190)
Footnote 190) This allows implementations to parallelize operations if there are no visible side effects.
7   EXAMPLE        The function atoi may be used in any of several ways:
    -- by use of its associated header (possibly generating a macro expansion)
                 #include <stdlib.h>
                 const char *str;
                 /* ... */
                 i = atoi(str);
    -- by use of its associated header (assuredly generating a true function reference)

            #include <stdlib.h>
            #undef atoi
            const char *str;
            /* ... */
            i = atoi(str);
   or
            #include <stdlib.h>
            const char *str;
            /* ... */
            i = (atoi)(str);
-- by explicit declaration
            extern int atoi(const char *);
            const char *str;
            /* ... */
            i = atoi(str);

7.2 [Diagnostics ]


1   The header <assert.h> defines the assert and static_assert macros and
    refers to another macro,
            NDEBUG
    which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
    point in the source file where <assert.h> is included, the assert macro is defined
    simply as
            #define assert(ignore) ((void)0)
    The assert macro is redefined according to the current state of NDEBUG each time that
    <assert.h> is included.
2   The assert macro shall be implemented as a macro, not as an actual function. If the
    macro definition is suppressed in order to access an actual function, the behavior is
    undefined.
3   The macro
            static_assert
    expands to _Static_assert.

7.2.1 [Program diagnostics]

 Program diagnostics

7.2.1.1 [The assert macro]


1           #include <assert.h>
            void assert(scalar expression);
    Description
2   The assert macro puts diagnostic tests into programs; it expands to a void expression.
    When it is executed, if expression (which shall have a scalar type) is false (that is,
    compares equal to 0), the assert macro writes information about the particular call that
    failed (including the text of the argument, the name of the source file, the source line
    number, and the name of the enclosing function -- the latter are respectively the values of
    the preprocessing macros _ _FILE_ _ and _ _LINE_ _ and of the identifier
    _ _func_ _) on the standard error stream in an implementation-defined format.191) It
    then calls the abort function.
    Returns
Footnote 191) The message written might be of the form:
          Assertion failed: expression, function abc, file xyz, line nnn.
3   The assert macro returns no value.
    Forward references: the abort function (7.22.4.1).

7.3 [Complex arithmetic ]

 Complex arithmetic 

7.3.1 [Introduction]


1   The header <complex.h> defines macros and declares functions that support complex
    arithmetic.192)
Footnote 192) See ``future library directions'' (7.31.1).
2   Implementations that define the macro _ _STDC_NO_COMPLEX_ _ need not provide
    this header nor support any of its facilities.
3   Each synopsis specifies a family of functions consisting of a principal function with one
    or more double complex parameters and a double complex or double return
    value; and other functions with the same name but with f and l suffixes which are
    corresponding functions with float and long double parameters and return values.
4   The macro
             complex
    expands to _Complex; the macro
             _Complex_I
    expands to a constant expression of type const float _Complex, with the value of
    the imaginary unit.193)
Footnote 193) The imaginary unit is a number i such that i 2   = -1.
5   The macros
             imaginary
    and
             _Imaginary_I
    are defined if and only if the implementation supports imaginary types;194) if defined,
    they expand to _Imaginary and a constant expression of type const float
    _Imaginary with the value of the imaginary unit.
Footnote 194) A specification for imaginary types is in informative annex G.
6   The macro
             I
    expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
    defined, I shall expand to _Complex_I.
7   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
    redefine the macros complex, imaginary, and I.

    Forward references: IEC 60559-compatible complex arithmetic (annex G).

7.3.2 [Conventions]


1   Values are interpreted as radians, not degrees. An implementation may set errno but is
    not required to.

7.3.3 [Branch cuts]


1   Some of the functions below have branch cuts, across which the function is
    discontinuous. For implementations with a signed zero (including all IEC 60559
    implementations) that follow the specifications of annex G, the sign of zero distinguishes
    one side of a cut from another so the function is continuous (except for format
    limitations) as the cut is approached from either side. For example, for the square root
    function, which has a branch cut along the negative real axis, the top of the cut, with
    imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
    imaginary part -0, maps to the negative imaginary axis.
2   Implementations that do not support a signed zero (see annex F) cannot distinguish the
    sides of branch cuts. These implementations shall map a cut so the function is continuous
    as the cut is approached coming around the finite endpoint of the cut in a counter
    clockwise direction. (Branch cuts for the functions specified here have just one finite
    endpoint.) For example, for the square root function, coming counter clockwise around
    the finite endpoint of the cut along the negative real axis approaches the cut from above,
    so the cut maps to the positive imaginary axis.

7.3.4 [The CX_LIMITED_RANGE pragma]


1            #include <complex.h>
             #pragma STDC CX_LIMITED_RANGE on-off-switch
    Description
2   The usual mathematical formulas for complex multiply, divide, and absolute value are
    problematic because of their treatment of infinities and because of undue overflow and
    underflow. The CX_LIMITED_RANGE pragma can be used to inform the
    implementation that (where the state is ``on'') the usual mathematical formulas are
    acceptable.195) The pragma can occur either outside external declarations or preceding all
    explicit declarations and statements inside a compound statement. When outside external
    declarations, the pragma takes effect from its occurrence until another
    CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
    When inside a compound statement, the pragma takes effect from its occurrence until
    another CX_LIMITED_RANGE pragma is encountered (including within a nested
    compound statement), or until the end of the compound statement; at the end of a
    compound statement the state for the pragma is restored to its condition just before the

    compound statement. If this pragma is used in any other context, the behavior is
    undefined. The default state for the pragma is ``off''.
Footnote 195) The purpose of the pragma is to allow the implementation to use the formulas:
             ( x + iy ) × (u + iv ) = ( xu - yv ) + i ( yu + xv )
             ( x + iy ) / (u + iv ) = [( xu + yv ) + i ( yu - xv )]/(u2 + v 2 )
             | x + iy | =  x 2 + y2
          where the programmer can determine they are safe.

7.3.5 [Trigonometric functions]

 Trigonometric functions

7.3.5.1 [The cacos functions]


1            #include <complex.h>
             double complex cacos(double complex z);
             float complex cacosf(float complex z);
             long double complex cacosl(long double complex z);
    Description
2   The cacos functions compute the complex arc cosine of z, with branch cuts outside the
    interval [-1, +1] along the real axis.
    Returns
3   The cacos functions return the complex arc cosine value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [0,  ] along the
    real axis.

7.3.5.2 [The casin functions]


1            #include <complex.h>
             double complex casin(double complex z);
             float complex casinf(float complex z);
             long double complex casinl(long double complex z);
    Description
2   The casin functions compute the complex arc sine of z, with branch cuts outside the
    interval [-1, +1] along the real axis.
    Returns
3   The casin functions return the complex arc sine value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [- /2, + /2]

    along the real axis.

7.3.5.3 [The catan functions]


1           #include <complex.h>
            double complex catan(double complex z);
            float complex catanf(float complex z);
            long double complex catanl(long double complex z);
    Description
2   The catan functions compute the complex arc tangent of z, with branch cuts outside the
    interval [-i , +i ] along the imaginary axis.
    Returns
3   The catan functions return the complex arc tangent value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [- /2, + /2]
    along the real axis.

7.3.5.4 [The ccos functions]


1           #include <complex.h>
            double complex ccos(double complex z);
            float complex ccosf(float complex z);
            long double complex ccosl(long double complex z);
    Description
2   The ccos functions compute the complex cosine of z.
    Returns
3   The ccos functions return the complex cosine value.

7.3.5.5 [The csin functions]


1           #include <complex.h>
            double complex csin(double complex z);
            float complex csinf(float complex z);
            long double complex csinl(long double complex z);
    Description
2   The csin functions compute the complex sine of z.

    Returns
3   The csin functions return the complex sine value.

7.3.5.6 [The ctan functions]


1          #include <complex.h>
           double complex ctan(double complex z);
           float complex ctanf(float complex z);
           long double complex ctanl(long double complex z);
    Description
2   The ctan functions compute the complex tangent of z.
    Returns
3   The ctan functions return the complex tangent value.

7.3.6 [Hyperbolic functions]

 Hyperbolic functions

7.3.6.1 [The cacosh functions]


1          #include <complex.h>
           double complex cacosh(double complex z);
           float complex cacoshf(float complex z);
           long double complex cacoshl(long double complex z);
    Description
2   The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
    cut at values less than 1 along the real axis.
    Returns
3   The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
    half-strip of nonnegative values along the real axis and in the interval [-i , +i ] along the
    imaginary axis.

7.3.6.2 [The casinh functions]


1          #include <complex.h>
           double complex casinh(double complex z);
           float complex casinhf(float complex z);
           long double complex casinhl(long double complex z);

    Description
2   The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
    outside the interval [-i , +i ] along the imaginary axis.
    Returns
3   The casinh functions return the complex arc hyperbolic sine value, in the range of a
    strip mathematically unbounded along the real axis and in the interval [-i /2, +i /2]
    along the imaginary axis.

7.3.6.3 [The catanh functions]


1           #include <complex.h>
            double complex catanh(double complex z);
            float complex catanhf(float complex z);
            long double complex catanhl(long double complex z);
    Description
2   The catanh functions compute the complex arc hyperbolic tangent of z, with branch
    cuts outside the interval [-1, +1] along the real axis.
    Returns
3   The catanh functions return the complex arc hyperbolic tangent value, in the range of a
    strip mathematically unbounded along the real axis and in the interval [-i /2, +i /2]
    along the imaginary axis.

7.3.6.4 [The ccosh functions]


1           #include <complex.h>
            double complex ccosh(double complex z);
            float complex ccoshf(float complex z);
            long double complex ccoshl(long double complex z);
    Description
2   The ccosh functions compute the complex hyperbolic cosine of z.
    Returns
3   The ccosh functions return the complex hyperbolic cosine value.

7.3.6.5 [The csinh functions]


1          #include <complex.h>
           double complex csinh(double complex z);
           float complex csinhf(float complex z);
           long double complex csinhl(long double complex z);
    Description
2   The csinh functions compute the complex hyperbolic sine of z.
    Returns
3   The csinh functions return the complex hyperbolic sine value.

7.3.6.6 [The ctanh functions]


1          #include <complex.h>
           double complex ctanh(double complex z);
           float complex ctanhf(float complex z);
           long double complex ctanhl(long double complex z);
    Description
2   The ctanh functions compute the complex hyperbolic tangent of z.
    Returns
3   The ctanh functions return the complex hyperbolic tangent value.

7.3.7 [Exponential and logarithmic functions]

 Exponential and logarithmic functions

7.3.7.1 [The cexp functions]


1          #include <complex.h>
           double complex cexp(double complex z);
           float complex cexpf(float complex z);
           long double complex cexpl(long double complex z);
    Description
2   The cexp functions compute the complex base-e exponential of z.
    Returns
3   The cexp functions return the complex base-e exponential value.


7.3.7.2 [The clog functions]


1           #include <complex.h>
            double complex clog(double complex z);
            float complex clogf(float complex z);
            long double complex clogl(long double complex z);
    Description
2   The clog functions compute the complex natural (base-e) logarithm of z, with a branch
    cut along the negative real axis.
    Returns
3   The clog functions return the complex natural logarithm value, in the range of a strip
    mathematically unbounded along the real axis and in the interval [-i , +i ] along the
    imaginary axis.

7.3.8 [Power and absolute-value functions]

 Power and absolute-value functions

7.3.8.1 [The cabs functions]


1           #include <complex.h>
            double cabs(double complex z);
            float cabsf(float complex z);
            long double cabsl(long double complex z);
    Description
2   The cabs functions compute the complex absolute value (also called norm, modulus, or
    magnitude) of z.
    Returns
3   The cabs functions return the complex absolute value.

7.3.8.2 [The cpow functions]


1           #include <complex.h>
            double complex cpow(double complex x, double complex y);
            float complex cpowf(float complex x, float complex y);
            long double complex cpowl(long double complex x,
                 long double complex y);
    Description
2   The cpow functions compute the complex power function xy , with a branch cut for the
    first parameter along the negative real axis.
    Returns
3   The cpow functions return the complex power function value.

7.3.8.3 [The csqrt functions]


1          #include <complex.h>
           double complex csqrt(double complex z);
           float complex csqrtf(float complex z);
           long double complex csqrtl(long double complex z);
    Description
2   The csqrt functions compute the complex square root of z, with a branch cut along the
    negative real axis.
    Returns
3   The csqrt functions return the complex square root value, in the range of the right half-
    plane (including the imaginary axis).

7.3.9 [Manipulation functions]

 Manipulation functions

7.3.9.1 [The carg functions]


1          #include <complex.h>
           double carg(double complex z);
           float cargf(float complex z);
           long double cargl(long double complex z);
    Description
2   The carg functions compute the argument (also called phase angle) of z, with a branch
    cut along the negative real axis.
    Returns
3   The carg functions return the value of the argument in the interval [- , + ].

7.3.9.2 [The cimag functions]


1           #include <complex.h>
            double cimag(double complex z);
            float cimagf(float complex z);
            long double cimagl(long double complex z);
    Description
2   The cimag functions compute the imaginary part of z.196)
    Returns
Footnote 196) For a variable z of complex type, z == creal(z) + cimag(z)*I.
3   The cimag functions return the imaginary part value (as a real).

7.3.9.3 [The CMPLX macros]


1           #include <complex.h>
            double complex CMPLX(double x, double y);
            float complex CMPLXF(float x, float y);
            long double complex CMPLXL(long double x, long double y);
    Description
2   The CMPLX macros expand to an expression of the specified complex type, with the real
    part having the (converted) value of x and the imaginary part having the (converted)
    value of y. The resulting expression shall be suitable for use as an initializer for an object
    with static or thread storage duration, provided both arguments are likewise suitable.
    Returns
3   The CMPLX macros return the complex value x + i y.
4   NOTE    These macros act as if the implementation supported imaginary types and the definitions were:
         #define CMPLX(x, y)  ((double complex)((double)(x) + \
                                       _Imaginary_I * (double)(y)))
         #define CMPLXF(x, y) ((float complex)((float)(x) + \
                                       _Imaginary_I * (float)(y)))
         #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
                                       _Imaginary_I * (long double)(y)))


7.3.9.4 [The conj functions]


1          #include <complex.h>
           double complex conj(double complex z);
           float complex conjf(float complex z);
           long double complex conjl(long double complex z);
    Description
2   The conj functions compute the complex conjugate of z, by reversing the sign of its
    imaginary part.
    Returns
3   The conj functions return the complex conjugate value.

7.3.9.5 [The cproj functions]


1          #include <complex.h>
           double complex cproj(double complex z);
           float complex cprojf(float complex z);
           long double complex cprojl(long double complex z);
    Description
2   The cproj functions compute a projection of z onto the Riemann sphere: z projects to
    z except that all complex infinities (even those with one infinite part and one NaN part)
    project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
    equivalent to
           INFINITY + I * copysign(0.0, cimag(z))
    Returns
3   The cproj functions return the value of the projection onto the Riemann sphere.

7.3.9.6 [The creal functions]


1          #include <complex.h>
           double creal(double complex z);
           float crealf(float complex z);
           long double creall(long double complex z);
    Description
2   The creal functions compute the real part of z.197)
    Returns
Footnote 197) For a variable z of complex type, z == creal(z) + cimag(z)*I.
3   The creal functions return the real part value.


7.4 [Character handling ]


1   The header <ctype.h> declares several functions useful for classifying and mapping
    characters.198) In all cases the argument is an int, the value of which shall be
    representable as an unsigned char or shall equal the value of the macro EOF. If the
    argument has any other value, the behavior is undefined.
Footnote 198) See ``future library directions'' (7.31.2).
2   The behavior of these functions is affected by the current locale. Those functions that
    have locale-specific aspects only when not in the "C" locale are noted below.
3   The term printing character refers to a member of a locale-specific set of characters, each
    of which occupies one printing position on a display device; the term control character
    refers to a member of a locale-specific set of characters that are not printing
    characters.199) All letters and digits are printing characters.
    Forward references: EOF (7.21.1), localization (7.11).
Footnote 199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
         whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
         values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).

7.4.1 [Character classification functions]


1   The functions in this subclause return nonzero (true) if and only if the value of the
    argument c conforms to that in the description of the function.

7.4.1.1 [The isalnum function]


1            #include <ctype.h>
             int isalnum(int c);
    Description
2   The isalnum function tests for any character for which isalpha or isdigit is true.

7.4.1.2 [The isalpha function]


1            #include <ctype.h>
             int isalpha(int c);
    Description
2   The isalpha function tests for any character for which isupper or islower is true,
    or any character that is one of a locale-specific set of alphabetic characters for which

    none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale,
    isalpha returns true only for the characters for which isupper or islower is true.
Footnote 200) The functions islower and isupper test true or false separately for each of these additional
         characters; all four combinations are possible.

7.4.1.3 [The isblank function]


1           #include <ctype.h>
            int isblank(int c);
    Description
2   The isblank function tests for any character that is a standard blank character or is one
    of a locale-specific set of characters for which isspace is true and that is used to
    separate words within a line of text. The standard blank characters are the following:
    space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
    for the standard blank characters.

7.4.1.4 [The iscntrl function]


1           #include <ctype.h>
            int iscntrl(int c);
    Description
2   The iscntrl function tests for any control character.

7.4.1.5 [The isdigit function]


1           #include <ctype.h>
            int isdigit(int c);
    Description
2   The isdigit function tests for any decimal-digit character (as defined in 5.2.1).

7.4.1.6 [The isgraph function]


1           #include <ctype.h>
            int isgraph(int c);

    Description
2   The isgraph function tests for any printing character except space (' ').

7.4.1.7 [The islower function]


1          #include <ctype.h>
           int islower(int c);
    Description
2   The islower function tests for any character that is a lowercase letter or is one of a
    locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
    isspace is true. In the "C" locale, islower returns true only for the lowercase
    letters (as defined in 5.2.1).

7.4.1.8 [The isprint function]


1          #include <ctype.h>
           int isprint(int c);
    Description
2   The isprint function tests for any printing character including space (' ').

7.4.1.9 [The ispunct function]


1          #include <ctype.h>
           int ispunct(int c);
    Description
2   The ispunct function tests for any printing character that is one of a locale-specific set
    of punctuation characters for which neither isspace nor isalnum is true. In the "C"
    locale, ispunct returns true for every printing character for which neither isspace
    nor isalnum is true.

7.4.1.10 [The isspace function]


1          #include <ctype.h>
           int isspace(int c);
    Description
2   The isspace function tests for any character that is a standard white-space character or
    is one of a locale-specific set of characters for which isalnum is false. The standard

    white-space characters are the following: space (' '), form feed ('\f'), new-line
    ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
    "C" locale, isspace returns true only for the standard white-space characters.

7.4.1.11 [The isupper function]


1           #include <ctype.h>
            int isupper(int c);
    Description
2   The isupper function tests for any character that is an uppercase letter or is one of a
    locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
    isspace is true. In the "C" locale, isupper returns true only for the uppercase
    letters (as defined in 5.2.1).

7.4.1.12 [The isxdigit function]


1           #include <ctype.h>
            int isxdigit(int c);
    Description
2   The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).

7.4.2 [Character case mapping functions]

 Character case mapping functions

7.4.2.1 [The tolower function]


1           #include <ctype.h>
            int tolower(int c);
    Description
2   The tolower function converts an uppercase letter to a corresponding lowercase letter.
    Returns
3   If the argument is a character for which isupper is true and there are one or more
    corresponding characters, as specified by the current locale, for which islower is true,
    the tolower function returns one of the corresponding characters (always the same one
    for any given locale); otherwise, the argument is returned unchanged.

7.4.2.2 [The toupper function]


1          #include <ctype.h>
           int toupper(int c);
    Description
2   The toupper function converts a lowercase letter to a corresponding uppercase letter.
    Returns
3   If the argument is a character for which islower is true and there are one or more
    corresponding characters, as specified by the current locale, for which isupper is true,
    the toupper function returns one of the corresponding characters (always the same one
    for any given locale); otherwise, the argument is returned unchanged.

7.5 [Errors ]


1   The header <errno.h> defines several macros, all relating to the reporting of error
    conditions.
2   The macros are
             EDOM
             EILSEQ
             ERANGE
    which expand to integer constant expressions with type int, distinct positive values, and
    which are suitable for use in #if preprocessing directives; and
             errno
    which expands to a modifiable lvalue201) that has type int and thread local storage
    duration, the value of which is set to a positive error number by several library functions.
    If a macro definition is suppressed in order to access an actual object, or a program
    defines an identifier with the name errno, the behavior is undefined.
Footnote 201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
         resulting from a function call (for example, *errno()).
3   The value of errno in the initial thread is zero at program startup (the initial value of
    errno in other threads is an indeterminate value), but is never set to zero by any library
    function.202) The value of errno may be set to nonzero by a library function call
    whether or not there is an error, provided the use of errno is not documented in the
    description of the function in this International Standard.
Footnote 202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
         then inspect it before a subsequent library function call. Of course, a library function can save the
         value of errno on entry and then set it to zero, as long as the original value is restored if errno's
         value is still zero just before the return.
4   Additional macro definitions, beginning with E and a digit or E and an uppercase
    letter,203) may also be specified by the implementation.

Footnote 203) See ``future library directions'' (7.31.3).

7.6 [Floating-point environment ]


1   The header <fenv.h> defines several macros, and declares types and functions that
    provide access to the floating-point environment. The floating-point environment refers
    collectively to any floating-point status flags and control modes supported by the
    implementation.204) A floating-point status flag is a system variable whose value is set
    (but never cleared) when a floating-point exception is raised, which occurs as a side effect
    of exceptional floating-point arithmetic to provide auxiliary information.205) A floating-
    point control mode is a system variable whose value may be set by the user to affect the
    subsequent behavior of floating-point arithmetic.
Footnote 204) This header is designed to support the floating-point exception status flags and directed-rounding
         control modes required by IEC 60559, and other similar floating-point state information. It is also
         designed to facilitate code portability among all systems.
Footnote 205) A floating-point status flag is not an object and can be set more than once within an expression.
2   The floating-point environment has thread storage duration. The initial state for a
    thread's floating-point environment is the current state of the floating-point environment
    of the thread that creates it at the time of creation.
3   Certain programming conventions support the intended model of use for the floating-
    point environment:206)
    -- a function call does not alter its caller's floating-point control modes, clear its caller's
       floating-point status flags, nor depend on the state of its caller's floating-point status
       flags unless the function is so documented;
    -- a function call is assumed to require default floating-point control modes, unless its
       documentation promises otherwise;
    -- a function call is assumed to have the potential for raising floating-point exceptions,
       unless its documentation promises otherwise.
Footnote 206) With these conventions, a programmer can safely assume default floating-point control modes (or be
         unaware of them). The responsibilities associated with accessing the floating-point environment fall
         on the programmer or program that does so explicitly.
4   The type
             fenv_t
    represents the entire floating-point environment.
5   The type
             fexcept_t
    represents the floating-point status flags collectively, including any status the
    implementation associates with the flags.

6   Each of the macros
             FE_DIVBYZERO
             FE_INEXACT
             FE_INVALID
             FE_OVERFLOW
             FE_UNDERFLOW
    is defined if and only if the implementation supports the floating-point exception by
    means of the functions in 7.6.2.207) Additional implementation-defined floating-point
    exceptions, with macro definitions beginning with FE_ and an uppercase letter,208) may
    also be specified by the implementation. The defined macros expand to integer constant
    expressions with values such that bitwise ORs of all combinations of the macros result in
    distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
    zero.209)
Footnote 207) The implementation supports a floating-point exception if there are circumstances where a call to at
         least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not
         necessary for all the functions to succeed all the time.
Footnote 208) See ``future library directions'' (7.31.4).
Footnote 209) The macros should be distinct powers of two.
7   The macro
             FE_ALL_EXCEPT
    is simply the bitwise OR of all floating-point exception macros defined by the
    implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
8   Each of the macros
             FE_DOWNWARD
             FE_TONEAREST
             FE_TOWARDZERO
             FE_UPWARD
    is defined if and only if the implementation supports getting and setting the represented
    rounding direction by means of the fegetround and fesetround functions.
    Additional implementation-defined rounding directions, with macro definitions beginning
    with FE_ and an uppercase letter,210) may also be specified by the implementation. The
    defined macros expand to integer constant expressions whose values are distinct
    nonnegative values.211)

Footnote 210) See ``future library directions'' (7.31.4).
Footnote 211) Even though the rounding direction macros may expand to constants corresponding to the values of
         FLT_ROUNDS, they are not required to do so.
9    The macro
              FE_DFL_ENV
     represents the default floating-point environment -- the one installed at program startup
     -- and has type ``pointer to const-qualified fenv_t''. It can be used as an argument to
     <fenv.h> functions that manage the floating-point environment.
10   Additional implementation-defined environments, with macro definitions beginning with
     FE_ and an uppercase letter,212) and having type ``pointer to const-qualified fenv_t'',
     may also be specified by the implementation.
Footnote 212) See ``future library directions'' (7.31.4).

7.6.1 [The FENV_ACCESS pragma]


1             #include <fenv.h>
              #pragma STDC FENV_ACCESS on-off-switch
     Description
2    The FENV_ACCESS pragma provides a means to inform the implementation when a
     program might access the floating-point environment to test floating-point status flags or
     run under non-default floating-point control modes.213) The pragma shall occur either
     outside external declarations or preceding all explicit declarations and statements inside a
     compound statement. When outside external declarations, the pragma takes effect from
     its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
     the translation unit. When inside a compound statement, the pragma takes effect from its
     occurrence until another FENV_ACCESS pragma is encountered (including within a
     nested compound statement), or until the end of the compound statement; at the end of a
     compound statement the state for the pragma is restored to its condition just before the
     compound statement. If this pragma is used in any other context, the behavior is
     undefined. If part of a program tests floating-point status flags, sets floating-point control
     modes, or runs under non-default mode settings, but was translated with the state for the
     FENV_ACCESS pragma ``off'', the behavior is undefined. The default state (``on'' or
     ``off'') for the pragma is implementation-defined. (When execution passes from a part of
     the program translated with FENV_ACCESS ``off'' to a part translated with
     FENV_ACCESS ``on'', the state of the floating-point status flags is unspecified and the
     floating-point control modes have their default settings.)

Footnote 213) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
          tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
          folding). In general, if the state of FENV_ACCESS is ``off'', the translator can assume that default
          modes are in effect and the flags are not tested.
3   EXAMPLE
            #include <fenv.h>
            void f(double x)
            {
                  #pragma STDC FENV_ACCESS ON
                  void g(double);
                  void h(double);
                  /* ... */
                  g(x + 1);
                  h(x + 1);
                  /* ... */
            }
4   If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
    x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
    contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.214)

Footnote 214) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
         hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
         ``off'', just one evaluation of x + 1 would suffice.

7.6.2 [Floating-point exceptions]


1   The following functions provide access to the floating-point status flags.215) The int
    input argument for the functions represents a subset of floating-point exceptions, and can
    be zero or the bitwise OR of one or more floating-point exception macros, for example
    FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
    functions is undefined.
Footnote 215) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
         abstraction of flags that are either set or clear. An implementation may endow floating-point status
         flags with more information -- for example, the address of the code which first raised the floating-
         point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
         content of flags.

7.6.2.1 [The feclearexcept function]


1           #include <fenv.h>
            int feclearexcept(int excepts);
    Description
2   The feclearexcept function attempts to clear the supported floating-point exceptions
    represented by its argument.
    Returns
3   The feclearexcept function returns zero if the excepts argument is zero or if all
    the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.


7.6.2.2 [The fegetexceptflag function]


1            #include <fenv.h>
             int fegetexceptflag(fexcept_t *flagp,
                  int excepts);
    Description
2   The fegetexceptflag function attempts to store an implementation-defined
    representation of the states of the floating-point status flags indicated by the argument
    excepts in the object pointed to by the argument flagp.
    Returns
3   The fegetexceptflag function returns zero if the representation was successfully
    stored. Otherwise, it returns a nonzero value.

7.6.2.3 [The feraiseexcept function]


1            #include <fenv.h>
             int feraiseexcept(int excepts);
    Description
2   The feraiseexcept function attempts to raise the supported floating-point exceptions
    represented by its argument.216) The order in which these floating-point exceptions are
    raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
    additionally raises the ``inexact'' floating-point exception whenever it raises the
    ``overflow'' or ``underflow'' floating-point exception is implementation-defined.
    Returns
Footnote 216) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
         Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
         in F.8.6 is in the same spirit.
3   The feraiseexcept function returns zero if the excepts argument is zero or if all
    the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.


7.6.2.4 [The fesetexceptflag function]


1            #include <fenv.h>
             int fesetexceptflag(const fexcept_t *flagp,
                  int excepts);
    Description
2   The fesetexceptflag function attempts to set the floating-point status flags
    indicated by the argument excepts to the states stored in the object pointed to by
    flagp. The value of *flagp shall have been set by a previous call to
    fegetexceptflag whose second argument represented at least those floating-point
    exceptions represented by the argument excepts. This function does not raise floating-
    point exceptions, but only sets the state of the flags.
    Returns
3   The fesetexceptflag function returns zero if the excepts argument is zero or if
    all the specified flags were successfully set to the appropriate state. Otherwise, it returns
    a nonzero value.

7.6.2.5 [The fetestexcept function]


1            #include <fenv.h>
             int fetestexcept(int excepts);
    Description
2   The fetestexcept function determines which of a specified subset of the floating-
    point exception flags are currently set. The excepts argument specifies the floating-
    point status flags to be queried.217)
    Returns
Footnote 217) This mechanism allows testing several floating-point exceptions with just one function call.
3   The fetestexcept function returns the value of the bitwise OR of the floating-point
    exception macros corresponding to the currently set floating-point exceptions included in
    excepts.
4   EXAMPLE       Call f if ``invalid'' is set, then g if ``overflow'' is set:

           #include <fenv.h>
           /* ... */
           {
                   #pragma STDC FENV_ACCESS ON
                   int set_excepts;
                   feclearexcept(FE_INVALID | FE_OVERFLOW);
                   // maybe raise exceptions
                   set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
                   if (set_excepts & FE_INVALID) f();
                   if (set_excepts & FE_OVERFLOW) g();
                   /* ... */
           }


7.6.3 [Rounding]


1   The fegetround and fesetround functions provide control of rounding direction
    modes.

7.6.3.1 [The fegetround function]


1          #include <fenv.h>
           int fegetround(void);
    Description
2   The fegetround function gets the current rounding direction.
    Returns
3   The fegetround function returns the value of the rounding direction macro
    representing the current rounding direction or a negative value if there is no such
    rounding direction macro or the current rounding direction is not determinable.

7.6.3.2 [The fesetround function]


1          #include <fenv.h>
           int fesetround(int round);
    Description
2   The fesetround function establishes the rounding direction represented by its
    argument round. If the argument is not equal to the value of a rounding direction macro,
    the rounding direction is not changed.
    Returns
3   The fesetround function returns zero if and only if the requested rounding direction
    was established.
4   EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
    rounding direction fails.
            #include <fenv.h>
            #include <assert.h>
            void f(int round_dir)
            {
                  #pragma STDC FENV_ACCESS ON
                  int save_round;
                  int setround_ok;
                  save_round = fegetround();
                  setround_ok = fesetround(round_dir);
                  assert(setround_ok == 0);
                  /* ... */
                  fesetround(save_round);
                  /* ... */
            }


7.6.4 [Environment]


1   The functions in this section manage the floating-point environment -- status flags and
    control modes -- as one entity.

7.6.4.1 [The fegetenv function]


1           #include <fenv.h>
            int fegetenv(fenv_t *envp);
    Description
2   The fegetenv function attempts to store the current floating-point environment in the
    object pointed to by envp.
    Returns
3   The fegetenv function returns zero if the environment was successfully stored.
    Otherwise, it returns a nonzero value.

7.6.4.2 [The feholdexcept function]


1           #include <fenv.h>
            int feholdexcept(fenv_t *envp);
    Description
2   The feholdexcept function saves the current floating-point environment in the object
    pointed to by envp, clears the floating-point status flags, and then installs a non-stop
    (continue on floating-point exceptions) mode, if available, for all floating-point
    exceptions.218)

    Returns
Footnote 218) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
         handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
         such systems, the feholdexcept function can be used in conjunction with the feupdateenv
         function to write routines that hide spurious floating-point exceptions from their callers.
3   The feholdexcept function returns zero if and only if non-stop floating-point
    exception handling was successfully installed.

7.6.4.3 [The fesetenv function]


1           #include <fenv.h>
            int fesetenv(const fenv_t *envp);
    Description
2   The fesetenv function attempts to establish the floating-point environment represented
    by the object pointed to by envp. The argument envp shall point to an object set by a
    call to fegetenv or feholdexcept, or equal a floating-point environment macro.
    Note that fesetenv merely installs the state of the floating-point status flags
    represented through its argument, and does not raise these floating-point exceptions.
    Returns
3   The fesetenv function returns zero if the environment was successfully established.
    Otherwise, it returns a nonzero value.

7.6.4.4 [The feupdateenv function]


1           #include <fenv.h>
            int feupdateenv(const fenv_t *envp);
    Description
2   The feupdateenv function attempts to save the currently raised floating-point
    exceptions in its automatic storage, install the floating-point environment represented by
    the object pointed to by envp, and then raise the saved floating-point exceptions. The
    argument envp shall point to an object set by a call to feholdexcept or fegetenv,
    or equal a floating-point environment macro.
    Returns
3   The feupdateenv function returns zero if all the actions were successfully carried out.
    Otherwise, it returns a nonzero value.

4   EXAMPLE     Hide spurious underflow floating-point exceptions:
            #include <fenv.h>
            double f(double x)
            {
                  #pragma STDC FENV_ACCESS ON
                  double result;
                  fenv_t save_env;
                  if (feholdexcept(&save_env))
                        return /* indication of an environmental problem */;
                  // compute result
                  if (/* test spurious underflow */)
                        if (feclearexcept(FE_UNDERFLOW))
                                 return /* indication of an environmental problem */;
                  if (feupdateenv(&save_env))
                        return /* indication of an environmental problem */;
                  return result;
            }

7.7 [Characteristics of floating types ]


1   The header <float.h> defines several macros that expand to various limits and
    parameters of the standard floating-point types.
2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
    in 5.2.4.2.2.

7.8 [Format conversion of integer types ]


1   The header <inttypes.h> includes the header <stdint.h> and extends it with
    additional facilities provided by hosted implementations.
2   It declares functions for manipulating greatest-width integers and converting numeric
    character strings to greatest-width integers, and it declares the type
             imaxdiv_t
    which is a structure type that is the type of the value returned by the imaxdiv function.
    For each type declared in <stdint.h>, it defines corresponding macros for conversion
    specifiers for use with the formatted input/output functions.219)
    Forward references: integer types <stdint.h> (7.20), formatted input/output
    functions (7.21.6), formatted wide character input/output functions (7.29.2).
Footnote 219) See ``future library directions'' (7.31.5).

7.8.1 [Macros for format specifiers]


1   Each of the following object-like macros expands to a character string literal containing a
    conversion specifier, possibly modified by a length modifier, suitable for use within the
    format argument of a formatted input/output function when converting the corresponding
    integer type. These macro names have the general form of PRI (character string literals
    for the fprintf and fwprintf family) or SCN (character string literals for the
    fscanf and fwscanf family),220) followed by the conversion specifier, followed by a
    name corresponding to a similar type name in 7.20.1. In these names, N represents the
    width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
    format string to print the value of an integer of type int_fast32_t.
Footnote 220) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
         different format specifiers may be required for fprintf and fscanf, even when the type is the
         same.
2   The fprintf macros for signed integers are:
           PRIdN             PRIdLEASTN                PRIdFASTN          PRIdMAX             PRIdPTR
           PRIiN             PRIiLEASTN                PRIiFASTN          PRIiMAX             PRIiPTR
3   The fprintf macros for unsigned integers are:
           PRIoN             PRIoLEASTN                PRIoFASTN          PRIoMAX             PRIoPTR
           PRIuN             PRIuLEASTN                PRIuFASTN          PRIuMAX             PRIuPTR
           PRIxN             PRIxLEASTN                PRIxFASTN          PRIxMAX             PRIxPTR
           PRIXN             PRIXLEASTN                PRIXFASTN          PRIXMAX             PRIXPTR
4   The fscanf macros for signed integers are:

           SCNdN           SCNdLEASTN               SCNdFASTN              SCNdMAX             SCNdPTR
           SCNiN           SCNiLEASTN               SCNiFASTN              SCNiMAX             SCNiPTR
5   The fscanf macros for unsigned integers are:
           SCNoN           SCNoLEASTN               SCNoFASTN              SCNoMAX             SCNoPTR
           SCNuN           SCNuLEASTN               SCNuFASTN              SCNuMAX             SCNuPTR
           SCNxN           SCNxLEASTN               SCNxFASTN              SCNxMAX             SCNxPTR
6   For each type that the implementation provides in <stdint.h>, the corresponding
    fprintf macros shall be defined and the corresponding fscanf macros shall be
    defined unless the implementation does not have a suitable fscanf length modifier for
    the type.
7   EXAMPLE
            #include <inttypes.h>
            #include <wchar.h>
            int main(void)
            {
                  uintmax_t i = UINTMAX_MAX;    // this type always exists
                  wprintf(L"The largest integer value is %020"
                        PRIxMAX "\n", i);
                  return 0;
            }


7.8.2 [Functions for greatest-width integer types]

 Functions for greatest-width integer types

7.8.2.1 [The imaxabs function]


1           #include <inttypes.h>
            intmax_t imaxabs(intmax_t j);
    Description
2   The imaxabs function computes the absolute value of an integer j. If the result cannot
    be represented, the behavior is undefined.221)
    Returns
Footnote 221) The absolute value of the most negative number cannot be represented in two's complement.
3   The imaxabs function returns the absolute value.


7.8.2.2 [The imaxdiv function]


1           #include <inttypes.h>
            imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
    Description
2   The imaxdiv function computes numer / denom and numer % denom in a single
    operation.
    Returns
3   The imaxdiv function returns a structure of type imaxdiv_t comprising both the
    quotient and the remainder. The structure shall contain (in either order) the members
    quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
    either part of the result cannot be represented, the behavior is undefined.

7.8.2.3 [The strtoimax and strtoumax functions]


1           #include <inttypes.h>
            intmax_t strtoimax(const char * restrict nptr,
                 char ** restrict endptr, int base);
            uintmax_t strtoumax(const char * restrict nptr,
                 char ** restrict endptr, int base);
    Description
2   The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
    strtoul, and strtoull functions, except that the initial portion of the string is
    converted to intmax_t and uintmax_t representation, respectively.
    Returns
3   The strtoimax and strtoumax functions return the converted value, if any. If no
    conversion could be performed, zero is returned. If the correct value is outside the range
    of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
    (according to the return type and sign of the value, if any), and the value of the macro
    ERANGE is stored in errno.
    Forward references: the strtol, strtoll, strtoul, and strtoull functions
    (7.22.1.4).

7.8.2.4 [The wcstoimax and wcstoumax functions]


1          #include <stddef.h>           // for wchar_t
           #include <inttypes.h>
           intmax_t wcstoimax(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr, int base);
           uintmax_t wcstoumax(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr, int base);
    Description
2   The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
    wcstoul, and wcstoull functions except that the initial portion of the wide string is
    converted to intmax_t and uintmax_t representation, respectively.
    Returns
3   The wcstoimax function returns the converted value, if any. If no conversion could be
    performed, zero is returned. If the correct value is outside the range of representable
    values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
    return type and sign of the value, if any), and the value of the macro ERANGE is stored in
    errno.
    Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
    (7.29.4.1.2).

7.9 [Alternative spellings ]


1   The header <iso646.h> defines the following eleven macros (on the left) that expand
    to the corresponding tokens (on the right):
            and        &&
            and_eq     &=
            bitand     &
            bitor      |
            compl      ~
            not        !
            not_eq     !=
            or         ||
            or_eq      |=
            xor        ^
            xor_eq     ^=

7.10 [Sizes of integer types ]


1   The header <limits.h> defines several macros that expand to various limits and
    parameters of the standard integer types.
2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
    in 5.2.4.2.1.

7.11 [Localization ]


1   The header <locale.h> declares two functions, one type, and defines several macros.
2   The type is
            struct lconv
    which contains members related to the formatting of numeric values. The structure shall
    contain at least the following members, in any order. The semantics of the members and
    their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
    the values specified in the comments.
            char   *decimal_point;                //   "."
            char   *thousands_sep;                //   ""
            char   *grouping;                     //   ""
            char   *mon_decimal_point;            //   ""
            char   *mon_thousands_sep;            //   ""
            char   *mon_grouping;                 //   ""
            char   *positive_sign;                //   ""
            char   *negative_sign;                //   ""
            char   *currency_symbol;              //   ""
            char   frac_digits;                   //   CHAR_MAX
            char   p_cs_precedes;                 //   CHAR_MAX
            char   n_cs_precedes;                 //   CHAR_MAX
            char   p_sep_by_space;                //   CHAR_MAX
            char   n_sep_by_space;                //   CHAR_MAX
            char   p_sign_posn;                   //   CHAR_MAX
            char   n_sign_posn;                   //   CHAR_MAX
            char   *int_curr_symbol;              //   ""
            char   int_frac_digits;               //   CHAR_MAX
            char   int_p_cs_precedes;             //   CHAR_MAX
            char   int_n_cs_precedes;             //   CHAR_MAX
            char   int_p_sep_by_space;            //   CHAR_MAX
            char   int_n_sep_by_space;            //   CHAR_MAX
            char   int_p_sign_posn;               //   CHAR_MAX
            char   int_n_sign_posn;               //   CHAR_MAX
3   The macros defined are NULL (described in 7.19); and
             LC_ALL
             LC_COLLATE
             LC_CTYPE
             LC_MONETARY
             LC_NUMERIC
             LC_TIME
    which expand to integer constant expressions with distinct values, suitable for use as the
    first argument to the setlocale function.222) Additional macro definitions, beginning
    with the characters LC_ and an uppercase letter,223) may also be specified by the
    implementation.
Footnote 222) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
Footnote 223) See ``future library directions'' (7.31.6).

7.11.1 [Locale control]

 Locale control

7.11.1.1 [The setlocale function]


1            #include <locale.h>
             char *setlocale(int category, const char *locale);
    Description
2   The setlocale function selects the appropriate portion of the program's locale as
    specified by the category and locale arguments. The setlocale function may be
    used to change or query the program's entire current locale or portions thereof. The value
    LC_ALL for category names the program's entire locale; the other values for
    category name only a portion of the program's locale. LC_COLLATE affects the
    behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
    the character handling functions224) and the multibyte and wide character functions.
    LC_MONETARY affects the monetary formatting information returned by the
    localeconv function. LC_NUMERIC affects the decimal-point character for the
    formatted input/output functions and the string conversion functions, as well as the
    nonmonetary formatting information returned by the localeconv function. LC_TIME
    affects the behavior of the strftime and wcsftime functions.
Footnote 224) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
         isxdigit.
3   A value of "C" for locale specifies the minimal environment for C translation; a value
    of "" for locale specifies the locale-specific native environment. Other
    implementation-defined strings may be passed as the second argument to setlocale.

4   At program startup, the equivalent of
            setlocale(LC_ALL, "C");
    is executed.
5   A call to the setlocale function may introduce a data race with other calls to the
    setlocale function or with calls to functions that are affected by the current locale.
    The implementation shall behave as if no library function calls the setlocale function.
    Returns
6   If a pointer to a string is given for locale and the selection can be honored, the
    setlocale function returns a pointer to the string associated with the specified
    category for the new locale. If the selection cannot be honored, the setlocale
    function returns a null pointer and the program's locale is not changed.
7   A null pointer for locale causes the setlocale function to return a pointer to the
    string associated with the category for the program's current locale; the program's
    locale is not changed.225)
Footnote 225) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
         locale when category has the value LC_ALL.
8   The pointer to string returned by the setlocale function is such that a subsequent call
    with that string value and its associated category will restore that part of the program's
    locale. The string pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the setlocale function.
    Forward references: formatted input/output functions (7.21.6), multibyte/wide
    character conversion functions (7.22.7), multibyte/wide string conversion functions
    (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.24.4.3), the
    strftime function (7.27.3.5), the strxfrm function (7.24.4.5).

7.11.2 [Numeric formatting convention inquiry]

 Numeric formatting convention inquiry

7.11.2.1 [The localeconv function]


1           #include <locale.h>
            struct lconv *localeconv(void);
    Description
2   The localeconv function sets the components of an object with type struct lconv
    with values appropriate for the formatting of numeric quantities (monetary and otherwise)
    according to the rules of the current locale.

3   The members of the structure with type char * are pointers to strings, any of which
    (except decimal_point) can point to "", to indicate that the value is not available in
    the current locale or is of zero length. Apart from grouping and mon_grouping, the
    strings shall start and end in the initial shift state. The members with type char are
    nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
    available in the current locale. The members include the following:
    char *decimal_point
              The decimal-point character used to format nonmonetary quantities.
    char *thousands_sep
              The character used to separate groups of digits before the decimal-point
              character in formatted nonmonetary quantities.
    char *grouping
              A string whose elements indicate the size of each group of digits in
              formatted nonmonetary quantities.
    char *mon_decimal_point
              The decimal-point used to format monetary quantities.
    char *mon_thousands_sep
              The separator for groups of digits before the decimal-point in formatted
              monetary quantities.
    char *mon_grouping
              A string whose elements indicate the size of each group of digits in
              formatted monetary quantities.
    char *positive_sign
              The string used to indicate a nonnegative-valued formatted monetary
              quantity.
    char *negative_sign
              The string used to indicate a negative-valued formatted monetary quantity.
    char *currency_symbol
              The local currency symbol applicable to the current locale.
    char frac_digits
              The number of fractional digits (those after the decimal-point) to be
              displayed in a locally formatted monetary quantity.
    char p_cs_precedes
              Set to 1 or 0 if the currency_symbol respectively precedes or
              succeeds the value for a nonnegative locally formatted monetary quantity.

char n_cs_precedes
          Set to 1 or 0 if the currency_symbol respectively precedes or
          succeeds the value for a negative locally formatted monetary quantity.
char p_sep_by_space
          Set to a value indicating the separation of the currency_symbol, the
          sign string, and the value for a nonnegative locally formatted monetary
          quantity.
char n_sep_by_space
          Set to a value indicating the separation of the currency_symbol, the
          sign string, and the value for a negative locally formatted monetary
          quantity.
char p_sign_posn
          Set to a value indicating the positioning of the positive_sign for a
          nonnegative locally formatted monetary quantity.
char n_sign_posn
          Set to a value indicating the positioning of the negative_sign for a
          negative locally formatted monetary quantity.
char *int_curr_symbol
          The international currency symbol applicable to the current locale. The
          first three characters contain the alphabetic international currency symbol
          in accordance with those specified in ISO 4217. The fourth character
          (immediately preceding the null character) is the character used to separate
          the international currency symbol from the monetary quantity.
char int_frac_digits
          The number of fractional digits (those after the decimal-point) to be
          displayed in an internationally formatted monetary quantity.
char int_p_cs_precedes
          Set to 1 or 0 if the int_curr_symbol respectively precedes or
          succeeds the value for a nonnegative internationally formatted monetary
          quantity.
char int_n_cs_precedes
          Set to 1 or 0 if the int_curr_symbol respectively precedes or
          succeeds the value for a negative internationally formatted monetary
          quantity.
char int_p_sep_by_space
          Set to a value indicating the separation of the int_curr_symbol, the
          sign string, and the value for a nonnegative internationally formatted
          monetary quantity.
    char int_n_sep_by_space
              Set to a value indicating the separation of the int_curr_symbol, the
              sign string, and the value for a negative internationally formatted monetary
              quantity.
    char int_p_sign_posn
              Set to a value indicating the positioning of the positive_sign for a
              nonnegative internationally formatted monetary quantity.
    char int_n_sign_posn
              Set to a value indicating the positioning of the negative_sign for a
              negative internationally formatted monetary quantity.
4   The elements of grouping and mon_grouping are interpreted according to the
    following:
    CHAR_MAX        No further grouping is to be performed.
    0               The previous element is to be repeatedly used for the remainder of the
                    digits.
    other           The integer value is the number of digits that compose the current group.
                    The next element is examined to determine the size of the next group of
                    digits before the current group.
5   The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
    and int_n_sep_by_space are interpreted according to the following:
    0     No space separates the currency symbol and value.
    1     If the currency symbol and sign string are adjacent, a space separates them from the
          value; otherwise, a space separates the currency symbol from the value.
    2   If the currency symbol and sign string are adjacent, a space separates them;
        otherwise, a space separates the sign string from the value.
    For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
    int_curr_symbol is used instead of a space.
6   The values of p_sign_posn, n_sign_posn, int_p_sign_posn,                              and
    int_n_sign_posn are interpreted according to the following:
    0     Parentheses surround the quantity and currency symbol.
    1     The sign string precedes the quantity and currency symbol.
    2     The sign string succeeds the quantity and currency symbol.
    3     The sign string immediately precedes the currency symbol.
    4     The sign string immediately succeeds the currency symbol.
7    The implementation shall behave as if no library function calls the localeconv
     function.
     Returns
8    The localeconv function returns a pointer to the filled-in object. The structure
     pointed to by the return value shall not be modified by the program, but may be
     overwritten by a subsequent call to the localeconv function. In addition, calls to the
     setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
     overwrite the contents of the structure.
9    EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
     monetary quantities.
                                   Local format                                     International format

     Country            Positive                  Negative                    Positive               Negative

     Country1     1.234,56 mk             -1.234,56 mk                  FIM   1.234,56         FIM -1.234,56
     Country2     L.1.234                 -L.1.234                      ITL   1.234            -ITL 1.234
     Country3      1.234,56                -1.234,56                    NLG   1.234,56         NLG -1.234,56
     Country4     SFrs.1,234.56           SFrs.1,234.56C                CHF   1,234.56         CHF 1,234.56C
10   For these four countries, the respective values for the monetary members of the structure returned by
     localeconv could be:
                                       Country1              Country2              Country3            Country4

     mon_decimal_point                 ","                   ""                   ","                 "."
     mon_thousands_sep                 "."                   "."                  "."                 ","
     mon_grouping                      "\3"                  "\3"                 "\3"                "\3"
     positive_sign                     ""                    ""                   ""                  ""
     negative_sign                     "-"                   "-"                  "-"                 "C"
     currency_symbol                   "mk"                  "L."                 "\u0192"            "SFrs."
     frac_digits                       2                     0                    2                   2
     p_cs_precedes                     0                     1                    1                   1
     n_cs_precedes                     0                     1                    1                   1
     p_sep_by_space                    1                     0                    1                   0
     n_sep_by_space                    1                     0                    2                   0
     p_sign_posn                       1                     1                    1                   1
     n_sign_posn                       1                     1                    4                   2
     int_curr_symbol                   "FIM "                "ITL "               "NLG "              "CHF "
     int_frac_digits                   2                     0                    2                   2
     int_p_cs_precedes                 1                     1                    1                   1
     int_n_cs_precedes                 1                     1                    1                   1
     int_p_sep_by_space                1                     1                    1                   1
     int_n_sep_by_space                2                     1                    2                   1
     int_p_sign_posn                   1                     1                    1                   1
     int_n_sign_posn                   4                     1                    4                   2
11   EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
     affect the formatted value.
                                                                   p_sep_by_space

     p_cs_precedes           p_sign_posn                0                   1                  2

                     0                    0         (1.25$)            (1.25 $)            (1.25$)
                                          1         +1.25$             +1.25 $             + 1.25$
                                          2         1.25$+             1.25 $+             1.25$ +
                                          3         1.25+$             1.25 +$             1.25+ $
                                          4         1.25$+             1.25 $+             1.25$ +

                     1                    0         ($1.25)            ($ 1.25)            ($1.25)
                                          1         +$1.25             +$ 1.25             + $1.25
                                          2         $1.25+             $ 1.25+             $1.25 +
                                          3         +$1.25             +$ 1.25             + $1.25
                                          4         $+1.25             $+ 1.25             $ +1.25

7.12 [Mathematics ]


1   The header <math.h> declares two types and many mathematical functions and defines
    several macros. Most synopses specify a family of functions consisting of a principal
    function with one or more double parameters, a double return value, or both; and
    other functions with the same name but with f and l suffixes, which are corresponding
    functions with float and long double parameters, return values, or both.226)
    Integer arithmetic functions and conversion functions are discussed later.
Footnote 226) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
         and return values in wider format than the synopsis prototype indicates.
2   The types
            float_t
            double_t
    are floating types at least as wide as float and double, respectively, and such that
    double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
    float_t and double_t are float and double, respectively; if
    FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
    2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
    otherwise implementation-defined.227)
Footnote 227) The types float_t and double_t are intended to be the implementation's most efficient types at
         least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
         type float_t is the narrowest type used by the implementation to evaluate floating expressions.
3   The macro
            HUGE_VAL
    expands to a positive double constant expression, not necessarily representable as a
    float. The macros
            HUGE_VALF
            HUGE_VALL
    are respectively float and long double analogs of HUGE_VAL.228)
Footnote 228) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
         supports infinities.
4   The macro
            INFINITY
    expands to a constant expression of type float representing positive or unsigned
    infinity, if available; else to a positive constant of type float that overflows at

    translation time.229)
Footnote 229) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
5   The macro
             NAN
    is defined if and only if the implementation supports quiet NaNs for the float type. It
    expands to a constant expression of type float representing a quiet NaN.
6   The number classification macros
             FP_INFINITE
             FP_NAN
             FP_NORMAL
             FP_SUBNORMAL
             FP_ZERO
    represent the mutually exclusive kinds of floating-point values. They expand to integer
    constant expressions with distinct values. Additional implementation-defined floating-
    point classifications, with macro definitions beginning with FP_ and an uppercase letter,
    may also be specified by the implementation.
7   The macro
             FP_FAST_FMA
    is optionally defined. If defined, it indicates that the fma function generally executes
    about as fast as, or faster than, a multiply and an add of double operands.230) The
    macros
             FP_FAST_FMAF
             FP_FAST_FMAL
    are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
    these macros expand to the integer constant 1.
Footnote 230) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
         directly with a hardware multiply-add instruction. Software implementations are expected to be
         substantially slower.
8   The macros
             FP_ILOGB0
             FP_ILOGBNAN
    expand to integer constant expressions whose values are returned by ilogb(x) if x is
    zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
    -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.

9   The macros
              MATH_ERRNO
              MATH_ERREXCEPT
    expand to the integer constants 1 and 2, respectively; the macro
            math_errhandling
    expands to an expression that has type int and the value MATH_ERRNO,
    MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
    constant for the duration of the program. It is unspecified whether
    math_errhandling is a macro or an identifier with external linkage. If a macro
    definition is suppressed or a program defines an identifier with the name
    math_errhandling, the behavior is undefined.              If the expression
    math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
    shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
    <fenv.h>.

7.12.1 [Treatment of error conditions]


1   The behavior of each of the functions in <math.h> is specified for all representable
    values of its input arguments, except where stated otherwise. Each function shall execute
    as if it were a single operation without raising SIGFPE and without generating any of the
    floating-point exceptions ``invalid'', ``divide-by-zero'', or ``overflow'' except to reflect
    the result of the function.
2   For all functions, a domain error occurs if an input argument is outside the domain over
    which the mathematical function is defined. The description of each function lists any
    required domain errors; an implementation may define additional domain errors, provided
    that such errors are consistent with the mathematical definition of the function.231) On a
    domain error, the function returns an implementation-defined value; if the integer
    expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
    errno acquires the value EDOM; if the integer expression math_errhandling &
    MATH_ERREXCEPT is nonzero, the ``invalid'' floating-point exception is raised.
Footnote 231) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
         error if the mathematical domain of the function does not include the infinity.
3   Similarly, a pole error (also known as a singularity or infinitary) occurs if the
    mathematical function has an exact infinite result as the finite input argument(s) are
    approached in the limit (for example, log(0.0)). The description of each function lists
    any required pole errors; an implementation may define additional pole errors, provided
    that such errors are consistent with the mathematical definition of the function. On a pole
    error, the function returns an implementation-defined value; if the integer expression

    math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
    acquires the value ERANGE; if the integer expression math_errhandling &
    MATH_ERREXCEPT is nonzero, the ``divide-by-zero'' floating-point exception is raised.
4   Likewise, a range error occurs if the mathematical result of the function cannot be
    represented in an object of the specified type, due to extreme magnitude.
5   A floating result overflows if the magnitude of the mathematical result is finite but so
    large that the mathematical result cannot be represented without extraordinary roundoff
    error in an object of the specified type. If a floating result overflows and default rounding
    is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or
    HUGE_VALL according to the return type, with the same sign as the correct value of the
    function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
    the integer expression errno acquires the value ERANGE; if the integer expression
    math_errhandling & MATH_ERREXCEPT is nonzero, the ``overflow'' floating-
    point exception is raised.
6   The result underflows if the magnitude of the mathematical result is so small that the
    mathematical result cannot be represented, without extraordinary roundoff error, in an
    object of the specified type.232) If the result underflows, the function returns an
    implementation-defined value whose magnitude is no greater than the smallest
    normalized positive number in the specified type; if the integer expression
    math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
    value     ERANGE       is    implementation-defined;     if   the integer  expression
    math_errhandling & MATH_ERREXCEPT is nonzero, whether the ``underflow''
    floating-point exception is raised is implementation-defined.
Footnote 232) The term underflow here is intended to encompass both ``gradual underflow'' as in IEC 60559 and
         also ``flush-to-zero'' underflow.
7   If a domain, pole, or range error occurs and the integer expression
    math_errhandling & MATH_ERRNO is zero,233) then errno shall either be set to
    the value corresponding to the error or left unmodified. If no such error occurs, errno
    shall be left unmodified regardless of the setting of math_errhandling.

Footnote 233) Math errors are being indicated by the floating-point exception flags rather than by errno.

7.12.2 [The FP_CONTRACT pragma]


1            #include <math.h>
             #pragma STDC FP_CONTRACT on-off-switch
    Description
2   The FP_CONTRACT pragma can be used to allow (if the state is ``on'') or disallow (if the
    state is ``off'') the implementation to contract expressions (6.5). Each pragma can occur
    either outside external declarations or preceding all explicit declarations and statements
    inside a compound statement. When outside external declarations, the pragma takes
    effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
    the end of the translation unit. When inside a compound statement, the pragma takes
    effect from its occurrence until another FP_CONTRACT pragma is encountered
    (including within a nested compound statement), or until the end of the compound
    statement; at the end of a compound statement the state for the pragma is restored to its
    condition just before the compound statement. If this pragma is used in any other
    context, the behavior is undefined. The default state (``on'' or ``off'') for the pragma is
    implementation-defined.

7.12.3 [Classification macros]


1   In the synopses in this subclause, real-floating indicates that the argument shall be an
    expression of real floating type.

7.12.3.1 [The fpclassify macro]


1            #include <math.h>
             int fpclassify(real-floating x);
    Description
2   The fpclassify macro classifies its argument value as NaN, infinite, normal,
    subnormal, zero, or into another implementation-defined category. First, an argument
    represented in a format wider than its semantic type is converted to its semantic type.
    Then classification is based on the type of the argument.234)
    Returns
Footnote 234) Since an expression can be evaluated with more range and precision than its type has, it is important to
         know the type that classification is based on. For example, a normal long double value might
         become subnormal when converted to double, and zero when converted to float.
3   The fpclassify macro returns the value of the number classification macro
    appropriate to the value of its argument.


7.12.3.2 [The isfinite macro]


1           #include <math.h>
            int isfinite(real-floating x);
    Description
2   The isfinite macro determines whether its argument has a finite value (zero,
    subnormal, or normal, and not infinite or NaN). First, an argument represented in a
    format wider than its semantic type is converted to its semantic type. Then determination
    is based on the type of the argument.
    Returns
3   The isfinite macro returns a nonzero value if and only if its argument has a finite
    value.

7.12.3.3 [The isinf macro]


1           #include <math.h>
            int isinf(real-floating x);
    Description
2   The isinf macro determines whether its argument value is an infinity (positive or
    negative). First, an argument represented in a format wider than its semantic type is
    converted to its semantic type. Then determination is based on the type of the argument.
    Returns
3   The isinf macro returns a nonzero value if and only if its argument has an infinite
    value.

7.12.3.4 [The isnan macro]


1           #include <math.h>
            int isnan(real-floating x);
    Description
2   The isnan macro determines whether its argument value is a NaN. First, an argument
    represented in a format wider than its semantic type is converted to its semantic type.
    Then determination is based on the type of the argument.235)

    Returns
Footnote 235) For the isnan macro, the type for determination does not matter unless the implementation supports
         NaNs in the evaluation type but not in the semantic type.
3   The isnan macro returns a nonzero value if and only if its argument has a NaN value.

7.12.3.5 [The isnormal macro]


1           #include <math.h>
            int isnormal(real-floating x);
    Description
2   The isnormal macro determines whether its argument value is normal (neither zero,
    subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
    semantic type is converted to its semantic type. Then determination is based on the type
    of the argument.
    Returns
3   The isnormal macro returns a nonzero value if and only if its argument has a normal
    value.

7.12.3.6 [The signbit macro]


1           #include <math.h>
            int signbit(real-floating x);
    Description
2   The signbit macro determines whether the sign of its argument value is negative.236)
    Returns
Footnote 236) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
         unsigned, it is treated as positive.
3   The signbit macro returns a nonzero value if and only if the sign of its argument value
    is negative.


7.12.4 [Trigonometric functions]

 Trigonometric functions

7.12.4.1 [The acos functions]


1          #include <math.h>
           double acos(double x);
           float acosf(float x);
           long double acosl(long double x);
    Description
2   The acos functions compute the principal value of the arc cosine of x. A domain error
    occurs for arguments not in the interval [-1, +1].
    Returns
3   The acos functions return arccos x in the interval [0,  ] radians.

7.12.4.2 [The asin functions]


1          #include <math.h>
           double asin(double x);
           float asinf(float x);
           long double asinl(long double x);
    Description
2   The asin functions compute the principal value of the arc sine of x. A domain error
    occurs for arguments not in the interval [-1, +1].
    Returns
3   The asin functions return arcsin x in the interval [- /2, + /2] radians.

7.12.4.3 [The atan functions]


1          #include <math.h>
           double atan(double x);
           float atanf(float x);
           long double atanl(long double x);
    Description
2   The atan functions compute the principal value of the arc tangent of x.
    Returns
3   The atan functions return arctan x in the interval [- /2, + /2] radians.

7.12.4.4 [The atan2 functions]


1           #include <math.h>
            double atan2(double y, double x);
            float atan2f(float y, float x);
            long double atan2l(long double y, long double x);
    Description
2   The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
    arguments to determine the quadrant of the return value. A domain error may occur if
    both arguments are zero.
    Returns
3   The atan2 functions return arctan y/x in the interval [- , + ] radians.

7.12.4.5 [The cos functions]


1           #include <math.h>
            double cos(double x);
            float cosf(float x);
            long double cosl(long double x);
    Description
2   The cos functions compute the cosine of x (measured in radians).
    Returns
3   The cos functions return cos x.

7.12.4.6 [The sin functions]


1           #include <math.h>
            double sin(double x);
            float sinf(float x);
            long double sinl(long double x);
    Description
2   The sin functions compute the sine of x (measured in radians).

    Returns
3   The sin functions return sin x.

7.12.4.7 [The tan functions]


1          #include <math.h>
           double tan(double x);
           float tanf(float x);
           long double tanl(long double x);
    Description
2   The tan functions return the tangent of x (measured in radians).
    Returns
3   The tan functions return tan x.

7.12.5 [Hyperbolic functions]

 Hyperbolic functions

7.12.5.1 [The acosh functions]


1          #include <math.h>
           double acosh(double x);
           float acoshf(float x);
           long double acoshl(long double x);
    Description
2   The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
    error occurs for arguments less than 1.
    Returns
3   The acosh functions return arcosh x in the interval [0, +].

7.12.5.2 [The asinh functions]


1          #include <math.h>
           double asinh(double x);
           float asinhf(float x);
           long double asinhl(long double x);
    Description
2   The asinh functions compute the arc hyperbolic sine of x.
    Returns
3   The asinh functions return arsinh x.

7.12.5.3 [The atanh functions]


1           #include <math.h>
            double atanh(double x);
            float atanhf(float x);
            long double atanhl(long double x);
    Description
2   The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
    for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
    -1 or +1.
    Returns
3   The atanh functions return artanh x.

7.12.5.4 [The cosh functions]


1           #include <math.h>
            double cosh(double x);
            float coshf(float x);
            long double coshl(long double x);
    Description
2   The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
    magnitude of x is too large.
    Returns
3   The cosh functions return cosh x.

7.12.5.5 [The sinh functions]


1           #include <math.h>
            double sinh(double x);
            float sinhf(float x);
            long double sinhl(long double x);
    Description
2   The sinh functions compute the hyperbolic sine of x. A range error occurs if the
    magnitude of x is too large.
    Returns
3   The sinh functions return sinh x.

7.12.5.6 [The tanh functions]


1          #include <math.h>
           double tanh(double x);
           float tanhf(float x);
           long double tanhl(long double x);
    Description
2   The tanh functions compute the hyperbolic tangent of x.
    Returns
3   The tanh functions return tanh x.

7.12.6 [Exponential and logarithmic functions]

 Exponential and logarithmic functions

7.12.6.1 [The exp functions]


1          #include <math.h>
           double exp(double x);
           float expf(float x);
           long double expl(long double x);
    Description
2   The exp functions compute the base-e exponential of x. A range error occurs if the
    magnitude of x is too large.
    Returns
3   The exp functions return ex .

7.12.6.2 [The exp2 functions]


1          #include <math.h>
           double exp2(double x);
           float exp2f(float x);
           long double exp2l(long double x);
    Description
2   The exp2 functions compute the base-2 exponential of x. A range error occurs if the
    magnitude of x is too large.

    Returns
3   The exp2 functions return 2x .

7.12.6.3 [The expm1 functions]


1           #include <math.h>
            double expm1(double x);
            float expm1f(float x);
            long double expm1l(long double x);
    Description
2   The expm1 functions compute the base-e exponential of the argument, minus 1. A range
    error occurs if x is too large.237)
    Returns
Footnote 237) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.
3   The expm1 functions return ex - 1.

7.12.6.4 [The frexp functions]


1           #include <math.h>
            double frexp(double value, int *exp);
            float frexpf(float value, int *exp);
            long double frexpl(long double value, int *exp);
    Description
2   The frexp functions break a floating-point number into a normalized fraction and an
    integral power of 2. They store the integer in the int object pointed to by exp.
    Returns
3   If value is not a floating-point number or if the integral power of 2 is outside the range
    of int, the results are unspecified. Otherwise, the frexp functions return the value x,
    such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x × 2*exp .
    If value is zero, both parts of the result are zero.

Footnote 1) This International Standard is designed to promote the portability of C programs among a variety of
         data-processing systems. It is intended for use by implementors and programmers.

7.12.6.5 [The ilogb functions]


1          #include <math.h>
           int ilogb(double x);
           int ilogbf(float x);
           int ilogbl(long double x);
    Description
2   The ilogb functions extract the exponent of x as a signed int value. If x is zero they
    compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
    a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
    the corresponding logb function and casting the returned value to type int. A domain
    error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
    the range of the return type, the numeric result is unspecified.
    Returns
3   The ilogb functions return the exponent of x as a signed int value.
    Forward references: the logb functions (7.12.6.11).

7.12.6.6 [The ldexp functions]


1          #include <math.h>
           double ldexp(double x, int exp);
           float ldexpf(float x, int exp);
           long double ldexpl(long double x, int exp);
    Description
2   The ldexp functions multiply a floating-point number by an integral power of 2. A
    range error may occur.
    Returns
3   The ldexp functions return x × 2exp .

7.12.6.7 [The log functions]


1          #include <math.h>
           double log(double x);
           float logf(float x);
           long double logl(long double x);

    Description
2   The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
    the argument is negative. A pole error may occur if the argument is zero.
    Returns
3   The log functions return loge x.

7.12.6.8 [The log10 functions]


1           #include <math.h>
            double log10(double x);
            float log10f(float x);
            long double log10l(long double x);
    Description
2   The log10 functions compute the base-10 (common) logarithm of x. A domain error
    occurs if the argument is negative. A pole error may occur if the argument is zero.
    Returns
3   The log10 functions return log10 x.

7.12.6.9 [The log1p functions]


1           #include <math.h>
            double log1p(double x);
            float log1pf(float x);
            long double log1pl(long double x);
    Description
2   The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.238)
    A domain error occurs if the argument is less than -1. A pole error may occur if the
    argument equals -1.
    Returns
Footnote 238) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).
3   The log1p functions return loge (1 + x).


7.12.6.10 [The log2 functions]


1          #include <math.h>
           double log2(double x);
           float log2f(float x);
           long double log2l(long double x);
    Description
2   The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
    argument is less than zero. A pole error may occur if the argument is zero.
    Returns
3   The log2 functions return log2 x.

7.12.6.11 [The logb functions]


1          #include <math.h>
           double logb(double x);
           float logbf(float x);
           long double logbl(long double x);
    Description
2   The logb functions extract the exponent of x, as a signed integer value in floating-point
    format. If x is subnormal it is treated as though it were normalized; thus, for positive
    finite x,
          1  x × FLT_RADIX-logb(x) < FLT_RADIX
    A domain error or pole error may occur if the argument is zero.
    Returns
3   The logb functions return the signed exponent of x.

7.12.6.12 [The modf functions]


1          #include <math.h>
           double modf(double value, double *iptr);
           float modff(float value, float *iptr);
           long double modfl(long double value, long double *iptr);
    Description
2   The modf functions break the argument value into integral and fractional parts, each of
    which has the same type and sign as the argument. They store the integral part (in
    floating-point format) in the object pointed to by iptr.
    Returns
3   The modf functions return the signed fractional part of value.

7.12.6.13 [The scalbn and scalbln functions]


1           #include <math.h>
            double scalbn(double x, int n);
            float scalbnf(float x, int n);
            long double scalbnl(long double x, int n);
            double scalbln(double x, long int n);
            float scalblnf(float x, long int n);
            long double scalblnl(long double x, long int n);
    Description
2   The scalbn and scalbln functions compute x × FLT_RADIXn efficiently, not
    normally by computing FLT_RADIXn explicitly. A range error may occur.
    Returns
3   The scalbn and scalbln functions return x × FLT_RADIXn .

7.12.7 [Power and absolute-value functions]

 Power and absolute-value functions

7.12.7.1 [The cbrt functions]


1           #include <math.h>
            double cbrt(double x);
            float cbrtf(float x);
            long double cbrtl(long double x);
    Description
2   The cbrt functions compute the real cube root of x.
    Returns
3   The cbrt functions return x1/3 .

7.12.7.2 [The fabs functions]


1          #include <math.h>
           double fabs(double x);
           float fabsf(float x);
           long double fabsl(long double x);
    Description
2   The fabs functions compute the absolute value of a floating-point number x.
    Returns
3   The fabs functions return | x |.

7.12.7.3 [The hypot functions]


1          #include <math.h>
           double hypot(double x, double y);
           float hypotf(float x, float y);
           long double hypotl(long double x, long double y);
    Description
2   The hypot functions compute the square root of the sum of the squares of x and y,
    without undue overflow or underflow. A range error may occur.
3   Returns
4   The hypot functions return  x2 + y 2 .

7.12.7.4 [The pow functions]


1          #include <math.h>
           double pow(double x, double y);
           float powf(float x, float y);
           long double powl(long double x, long double y);
    Description
2   The pow functions compute x raised to the power y. A domain error occurs if x is finite
    and negative and y is finite and not an integer value. A range error may occur. A domain
    error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
    zero and y is less than zero.
    Returns
3   The pow functions return xy .

7.12.7.5 [The sqrt functions]


1           #include <math.h>
            double sqrt(double x);
            float sqrtf(float x);
            long double sqrtl(long double x);
    Description
2   The sqrt functions compute the nonnegative square root of x. A domain error occurs if
    the argument is less than zero.
    Returns
3   The sqrt functions return x.
                              

7.12.8 [Error and gamma functions]

 Error and gamma functions

7.12.8.1 [The erf functions]


1           #include <math.h>
            double erf(double x);
            float erff(float x);
            long double erfl(long double x);
    Description
2   The erf functions compute the error function of x.
    Returns
3                                      2      x
                                                  e-t dt .
                                                     2
    The erf functions return erf x =
                                           0


7.12.8.2 [The erfc functions]


1           #include <math.h>
            double erfc(double x);
            float erfcf(float x);
            long double erfcl(long double x);
    Description
2   The erfc functions compute the complementary error function of x. A range error
    occurs if x is too large.
    Returns
3                                                       2      
                                                                  e-t dt .
                                                                     2
    The erfc functions return erfc x = 1 - erf x =
                                                            x


7.12.8.3 [The lgamma functions]


1          #include <math.h>
           double lgamma(double x);
           float lgammaf(float x);
           long double lgammal(long double x);
    Description
2   The lgamma functions compute the natural logarithm of the absolute value of gamma of
    x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
    or zero.
    Returns
3   The lgamma functions return loge | (x) |.

7.12.8.4 [The tgamma functions]


1          #include <math.h>
           double tgamma(double x);
           float tgammaf(float x);
           long double tgammal(long double x);
    Description
2   The tgamma functions compute the gamma function of x. A domain error or pole error
    may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
    too large and may occur if the magnitude of x is too small.
    Returns
3   The tgamma functions return (x).

7.12.9 [Nearest integer functions]

 Nearest integer functions

7.12.9.1 [The ceil functions]


1           #include <math.h>
            double ceil(double x);
            float ceilf(float x);
            long double ceill(long double x);
    Description
2   The ceil functions compute the smallest integer value not less than x.
    Returns
3   The ceil functions return x, expressed as a floating-point number.

7.12.9.2 [The floor functions]


1           #include <math.h>
            double floor(double x);
            float floorf(float x);
            long double floorl(long double x);
    Description
2   The floor functions compute the largest integer value not greater than x.
    Returns
3   The floor functions return x, expressed as a floating-point number.

7.12.9.3 [The nearbyint functions]


1           #include <math.h>
            double nearbyint(double x);
            float nearbyintf(float x);
            long double nearbyintl(long double x);
    Description
2   The nearbyint functions round their argument to an integer value in floating-point
    format, using the current rounding direction and without raising the ``inexact'' floating-
    point exception.
    Returns
3   The nearbyint functions return the rounded integer value.

7.12.9.4 [The rint functions]


1          #include <math.h>
           double rint(double x);
           float rintf(float x);
           long double rintl(long double x);
    Description
2   The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
    rint functions may raise the ``inexact'' floating-point exception if the result differs in
    value from the argument.
    Returns
3   The rint functions return the rounded integer value.

7.12.9.5 [The lrint and llrint functions]


1          #include <math.h>
           long int lrint(double x);
           long int lrintf(float x);
           long int lrintl(long double x);
           long long int llrint(double x);
           long long int llrintf(float x);
           long long int llrintl(long double x);
    Description
2   The lrint and llrint functions round their argument to the nearest integer value,
    rounding according to the current rounding direction. If the rounded value is outside the
    range of the return type, the numeric result is unspecified and a domain error or range
    error may occur.
    Returns
3   The lrint and llrint functions return the rounded integer value.

7.12.9.6 [The round functions]


1           #include <math.h>
            double round(double x);
            float roundf(float x);
            long double roundl(long double x);
    Description
2   The round functions round their argument to the nearest integer value in floating-point
    format, rounding halfway cases away from zero, regardless of the current rounding
    direction.
    Returns
3   The round functions return the rounded integer value.

7.12.9.7 [The lround and llround functions]


1           #include <math.h>
            long int lround(double x);
            long int lroundf(float x);
            long int lroundl(long double x);
            long long int llround(double x);
            long long int llroundf(float x);
            long long int llroundl(long double x);
    Description
2   The lround and llround functions round their argument to the nearest integer value,
    rounding halfway cases away from zero, regardless of the current rounding direction. If
    the rounded value is outside the range of the return type, the numeric result is unspecified
    and a domain error or range error may occur.
    Returns
3   The lround and llround functions return the rounded integer value.

7.12.9.8 [The trunc functions]


1           #include <math.h>
            double trunc(double x);
            float truncf(float x);
            long double truncl(long double x);
    Description
2   The trunc functions round their argument to the integer value, in floating format,
    nearest to but no larger in magnitude than the argument.
    Returns
3   The trunc functions return the truncated integer value.

7.12.10 [Remainder functions]

 Remainder functions

7.12.10.1 [The fmod functions]


1            #include <math.h>
             double fmod(double x, double y);
             float fmodf(float x, float y);
             long double fmodl(long double x, long double y);
    Description
2   The fmod functions compute the floating-point remainder of x/y.
    Returns
3   The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
    the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
    whether a domain error occurs or the fmod functions return zero is implementation-
    defined.

7.12.10.2 [The remainder functions]


1            #include <math.h>
             double remainder(double x, double y);
             float remainderf(float x, float y);
             long double remainderl(long double x, long double y);
    Description
2   The remainder functions compute the remainder x REM y required by IEC 60559.239)

    Returns
Footnote 239) ``When y  0, the remainder r = x REM y is defined regardless of the rounding mode by the
         mathematical relation r = x - ny , where n is the integer nearest the exact value of x / y ; whenever
         | n - x / y | = 1/2, then n is even. If r = 0, its sign shall be that of x .'' This definition is applicable for
         all implementations.
3   The remainder functions return x REM y. If y is zero, whether a domain error occurs
    or the functions return zero is implementation defined.

7.12.10.3 [The remquo functions]


1           #include <math.h>
            double remquo(double x, double y, int *quo);
            float remquof(float x, float y, int *quo);
            long double remquol(long double x, long double y,
                 int *quo);
    Description
2   The remquo functions compute the same remainder as the remainder functions. In
    the object pointed to by quo they store a value whose sign is the sign of x/y and whose
    magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
    n is an implementation-defined integer greater than or equal to 3.
    Returns
3   The remquo functions return x REM y. If y is zero, the value stored in the object
    pointed to by quo is unspecified and whether a domain error occurs or the functions
    return zero is implementation defined.

7.12.11 [Manipulation functions]

 Manipulation functions

7.12.11.1 [The copysign functions]


1           #include <math.h>
            double copysign(double x, double y);
            float copysignf(float x, float y);
            long double copysignl(long double x, long double y);
    Description
2   The copysign functions produce a value with the magnitude of x and the sign of y.
    They produce a NaN (with the sign of y) if x is a NaN. On implementations that
    represent a signed zero but do not treat negative zero consistently in arithmetic
    operations, the copysign functions regard the sign of zero as positive.
    Returns
3   The copysign functions return a value with the magnitude of x and the sign of y.


7.12.11.2 [The nan functions]


1           #include <math.h>
            double nan(const char *tagp);
            float nanf(const char *tagp);
            long double nanl(const char *tagp);
    Description
2   The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
    sequence)",     (char**)       NULL); the call nan("") is equivalent to
    strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
    sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
    NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
    and strtold.
    Returns
3   The nan functions return a quiet NaN, if available, with content indicated through tagp.
    If the implementation does not support quiet NaNs, the functions return zero.
    Forward references: the strtod, strtof, and strtold functions (7.22.1.3).

7.12.11.3 [The nextafter functions]


1           #include <math.h>
            double nextafter(double x, double y);
            float nextafterf(float x, float y);
            long double nextafterl(long double x, long double y);
    Description
2   The nextafter functions determine the next representable value, in the type of the
    function, after x in the direction of y, where x and y are first converted to the type of the
    function.240) The nextafter functions return y if x equals y. A range error may occur
    if the magnitude of x is the largest finite value representable in the type and the result is
    infinite or not representable in the type.
    Returns
Footnote 240) The argument values are converted to the type of the function, even by a macro implementation of the
         function.
3   The nextafter functions return the next representable value in the specified format
    after x in the direction of y.


7.12.11.4 [The nexttoward functions]


1           #include <math.h>
            double nexttoward(double x, long double y);
            float nexttowardf(float x, long double y);
            long double nexttowardl(long double x, long double y);
    Description
2   The nexttoward functions are equivalent to the nextafter functions except that the
    second parameter has type long double and the functions return y converted to the
    type of the function if x equals y.241)
Footnote 241) The result of the nexttoward functions is determined in the type of the function, without loss of
         range or precision in a floating second argument.

7.12.12 [Maximum, minimum, and positive difference functions]

 Maximum, minimum, and positive difference functions

7.12.12.1 [The fdim functions]


1           #include <math.h>
            double fdim(double x, double y);
            float fdimf(float x, float y);
            long double fdiml(long double x, long double y);
    Description
2   The fdim functions determine the positive difference between their arguments:
          x - y if x > y
          
          +0      if x  y
    A range error may occur.
    Returns
3   The fdim functions return the positive difference value.

7.12.12.2 [The fmax functions]


1           #include <math.h>
            double fmax(double x, double y);
            float fmaxf(float x, float y);
            long double fmaxl(long double x, long double y);

    Description
2   The fmax functions determine the maximum numeric value of their arguments.242)
    Returns
Footnote 242) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
         fmax functions choose the numeric value. See F.10.9.2.
3   The fmax functions return the maximum numeric value of their arguments.

7.12.12.3 [The fmin functions]


1           #include <math.h>
            double fmin(double x, double y);
            float fminf(float x, float y);
            long double fminl(long double x, long double y);
    Description
2   The fmin functions determine the minimum numeric value of their arguments.243)
    Returns
Footnote 243) The fmin functions are analogous to the fmax functions in their treatment of NaNs.
3   The fmin functions return the minimum numeric value of their arguments.

7.12.13 [Floating multiply-add]

 Floating multiply-add

7.12.13.1 [The fma functions]


1           #include <math.h>
            double fma(double x, double y, double z);
            float fmaf(float x, float y, float z);
            long double fmal(long double x, long double y,
                 long double z);
    Description
2   The fma functions compute (x × y) + z, rounded as one ternary operation: they compute
    the value (as if) to infinite precision and round once to the result format, according to the
    current rounding mode. A range error may occur.
    Returns
3   The fma functions return (x × y) + z, rounded as one ternary operation.


7.12.14 [Comparison macros]


1   The relational and equality operators support the usual mathematical relationships
    between numeric values. For any ordered pair of numeric values exactly one of the
    relationships -- less, greater , and equal -- is true. Relational operators may raise the
    ``invalid'' floating-point exception when argument values are NaNs. For a NaN and a
    numeric value, or for two NaNs, just the unordered relationship is true.244) The following
    subclauses provide macros that are quiet (non floating-point exception raising) versions
    of the relational operators, and other comparison macros that facilitate writing efficient
    code that accounts for NaNs without suffering the ``invalid'' floating-point exception. In
    the synopses in this subclause, real-floating indicates that the argument shall be an
    expression of real floating type245) (both arguments need not have the same type).246)
Footnote 244) IEC 60559 requires that the built-in relational operators raise the ``invalid'' floating-point exception if
         the operands compare unordered, as an error indicator for programs written without consideration of
         NaNs; the result in these cases is false.
Footnote 245) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
         undefined.
Footnote 246) Whether an argument represented in a format wider than its semantic type is converted to the semantic
         type is unspecified.

7.12.14.1 [The isgreater macro]


1            #include <math.h>
             int isgreater(real-floating x, real-floating y);
    Description
2   The isgreater macro determines whether its first argument is greater than its second
    argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
    unlike (x) > (y), isgreater(x, y) does not raise the ``invalid'' floating-point
    exception when x and y are unordered.
    Returns
3   The isgreater macro returns the value of (x) > (y).

7.12.14.2 [The isgreaterequal macro]


1            #include <math.h>
             int isgreaterequal(real-floating x, real-floating y);

    Description
2   The isgreaterequal macro determines whether its first argument is greater than or
    equal to its second argument. The value of isgreaterequal(x, y) is always equal
    to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
    not raise the ``invalid'' floating-point exception when x and y are unordered.
    Returns
3   The isgreaterequal macro returns the value of (x) >= (y).

7.12.14.3 [The isless macro]


1         #include <math.h>
          int isless(real-floating x, real-floating y);
    Description
2   The isless macro determines whether its first argument is less than its second
    argument. The value of isless(x, y) is always equal to (x) < (y); however,
    unlike (x) < (y), isless(x, y) does not raise the ``invalid'' floating-point
    exception when x and y are unordered.
    Returns
3   The isless macro returns the value of (x) < (y).

7.12.14.4 [The islessequal macro]


1         #include <math.h>
          int islessequal(real-floating x, real-floating y);
    Description
2   The islessequal macro determines whether its first argument is less than or equal to
    its second argument. The value of islessequal(x, y) is always equal to
    (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
    the ``invalid'' floating-point exception when x and y are unordered.
    Returns
3   The islessequal macro returns the value of (x) <= (y).

7.12.14.5 [The islessgreater macro]


1           #include <math.h>
            int islessgreater(real-floating x, real-floating y);
    Description
2   The islessgreater macro determines whether its first argument is less than or
    greater than its second argument. The islessgreater(x, y) macro is similar to
    (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
    the ``invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
    and y twice).
    Returns
3   The islessgreater macro returns the value of (x) < (y) || (x) > (y).

7.12.14.6 [The isunordered macro]


1           #include <math.h>
            int isunordered(real-floating x, real-floating y);
    Description
2   The isunordered macro determines whether its arguments are unordered.
    Returns
3   The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.

7.13 [Nonlocal jumps ]


1   The header <setjmp.h> defines the macro setjmp, and declares one function and
    one type, for bypassing the normal function call and return discipline.247)
Footnote 247) These functions are useful for dealing with unusual conditions encountered in a low-level function of
         a program.
2   The type declared is
            jmp_buf
    which is an array type suitable for holding the information needed to restore a calling
    environment. The environment of a call to the setjmp macro consists of information
    sufficient for a call to the longjmp function to return execution to the correct block and
    invocation of that block, were it called recursively. It does not include the state of the
    floating-point status flags, of open files, or of any other component of the abstract
    machine.
3   It is unspecified whether setjmp is a macro or an identifier declared with external
    linkage. If a macro definition is suppressed in order to access an actual function, or a
    program defines an external identifier with the name setjmp, the behavior is undefined.

7.13.1 [Save calling environment]

 Save calling environment

7.13.1.1 [The setjmp macro]


1           #include <setjmp.h>
            int setjmp(jmp_buf env);
    Description
2   The setjmp macro saves its calling environment in its jmp_buf argument for later use
    by the longjmp function.
    Returns
3   If the return is from a direct invocation, the setjmp macro returns the value zero. If the
    return is from a call to the longjmp function, the setjmp macro returns a nonzero
    value.
    Environmental limits
4   An invocation of the setjmp macro shall appear only in one of the following contexts:
    -- the entire controlling expression of a selection or iteration statement;
    -- one operand of a relational or equality operator with the other operand an integer
       constant expression, with the resulting expression being the entire controlling

        expression of a selection or iteration statement;
    -- the operand of a unary ! operator with the resulting expression being the entire
       controlling expression of a selection or iteration statement; or
    -- the entire expression of an expression statement (possibly cast to void).
5   If the invocation appears in any other context, the behavior is undefined.

7.13.2 [Restore calling environment]

 Restore calling environment

7.13.2.1 [The longjmp function]


1            #include <setjmp.h>
             _Noreturn void longjmp(jmp_buf env, int val);
    Description
2   The longjmp function restores the environment saved by the most recent invocation of
    the setjmp macro in the same invocation of the program with the corresponding
    jmp_buf argument. If there has been no such invocation, or if the invocation was from
    another thread of execution, or if the function containing the invocation of the setjmp
    macro has terminated execution248) in the interim, or if the invocation of the setjmp
    macro was within the scope of an identifier with variably modified type and execution has
    left that scope in the interim, the behavior is undefined.
Footnote 248) For example, by executing a return statement or because another longjmp call has caused a
         transfer to a setjmp invocation in a function earlier in the set of nested calls.
3   All accessible objects have values, and all other components of the abstract machine249)
    have state, as of the time the longjmp function was called, except that the values of
    objects of automatic storage duration that are local to the function containing the
    invocation of the corresponding setjmp macro that do not have volatile-qualified type
    and have been changed between the setjmp invocation and longjmp call are
    indeterminate.
    Returns
Footnote 249) This includes, but is not limited to, the floating-point status flags and the state of open files.
4   After longjmp is completed, thread execution continues as if the corresponding
    invocation of the setjmp macro had just returned the value specified by val. The
    longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
    the setjmp macro returns the value 1.
5   EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
    might cause memory associated with a variable length array object to be squandered.

      #include <setjmp.h>
      jmp_buf buf;
      void g(int n);
      void h(int n);
      int n = 6;
      void f(void)
      {
            int x[n];             // valid: f is not terminated
            setjmp(buf);
            g(n);
      }
      void g(int n)
      {
            int a[n];             // a may remain allocated
            h(n);
      }
      void h(int n)
      {
            int b[n];             // b may remain allocated
            longjmp(buf, 2);      // might cause memory loss
      }

7.14 [Signal handling ]


1   The header <signal.h> declares a type and two functions and defines several macros,
    for handling various signals (conditions that may be reported during program execution).
2   The type defined is
             sig_atomic_t
    which is the (possibly volatile-qualified) integer type of an object that can be accessed as
    an atomic entity, even in the presence of asynchronous interrupts.
3   The macros defined are
             SIG_DFL
             SIG_ERR
             SIG_IGN
    which expand to constant expressions with distinct values that have type compatible with
    the second argument to, and the return value of, the signal function, and whose values
    compare unequal to the address of any declarable function; and the following, which
    expand to positive integer constant expressions with type int and distinct values that are
    the signal numbers, each corresponding to the specified condition:
             SIGABRT abnormal termination, such as is initiated by the abort function
             SIGFPE        an erroneous arithmetic operation, such as zero divide or an operation
                           resulting in overflow
             SIGILL        detection of an invalid function image, such as an invalid instruction
             SIGINT        receipt of an interactive attention signal
             SIGSEGV an invalid access to storage
             SIGTERM a termination request sent to the program
4   An implementation need not generate any of these signals, except as a result of explicit
    calls to the raise function. Additional signals and pointers to undeclarable functions,
    with macro definitions beginning, respectively, with the letters SIG and an uppercase
    letter or with SIG_ and an uppercase letter,250) may also be specified by the
    implementation. The complete set of signals, their semantics, and their default handling
    is implementation-defined; all signal numbers shall be positive.

Footnote 250) See ``future library directions'' (7.31.7). The names of the signal numbers reflect the following terms
         (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
         and termination.

7.14.1 [Specify signal handling]

 Specify signal handling

7.14.1.1 [The signal function]


1            #include <signal.h>
             void (*signal(int sig, void (*func)(int)))(int);
    Description
2   The signal function chooses one of three ways in which receipt of the signal number
    sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
    for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
    Otherwise, func shall point to a function to be called when that signal occurs. An
    invocation of such a function because of a signal, or (recursively) of any further functions
    called by that invocation (other than functions in the standard library),251) is called a
    signal handler .
Footnote 251) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
         called via the abort function).
3   When a signal occurs and func points to a function, it is implementation-defined
    whether the equivalent of signal(sig, SIG_DFL); is executed or the
    implementation prevents some implementation-defined set of signals (at least including
    sig) from occurring until the current signal handling has completed; in the case of
    SIGILL, the implementation may alternatively define that no action is taken. Then the
    equivalent of (*func)(sig); is executed. If and when the function returns, if the
    value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
    value corresponding to a computational exception, the behavior is undefined; otherwise
    the program will resume execution at the point it was interrupted.
4   If the signal occurs as the result of calling the abort or raise function, the signal
    handler shall not call the raise function.
5   If the signal occurs other than as the result of calling the abort or raise function, the
    behavior is undefined if the signal handler refers to any object with static or thread
    storage duration that is not a lock-free atomic object other than by assigning a value to an
    object declared as volatile sig_atomic_t, or the signal handler calls any function
    in the standard library other than the abort function, the _Exit function, the
    quick_exit function, or the signal function with the first argument equal to the
    signal number corresponding to the signal that caused the invocation of the handler.
    Furthermore, if such a call to the signal function results in a SIG_ERR return, the
    value of errno is indeterminate.252)

Footnote 252) If any signal is generated by an asynchronous signal handler, the behavior is undefined.
6   At program startup, the equivalent of
            signal(sig, SIG_IGN);
    may be executed for some signals selected in an implementation-defined manner; the
    equivalent of
            signal(sig, SIG_DFL);
    is executed for all other signals defined by the implementation.
7   Use of this function in a multi-threaded program results in undefined behavior. The
    implementation shall behave as if no library function calls the signal function.
    Returns
8   If the request can be honored, the signal function returns the value of func for the
    most recent successful call to signal for the specified signal sig. Otherwise, a value of
    SIG_ERR is returned and a positive value is stored in errno.
    Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
    _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).

7.14.2 [Send signal]

 Send signal

7.14.2.1 [The raise function]


1           #include <signal.h>
            int raise(int sig);
    Description
2   The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
    signal handler is called, the raise function shall not return until after the signal handler
    does.
    Returns
3   The raise function returns zero if successful, nonzero if unsuccessful.

7.15 [Alignment ]


1   The header <stdalign.h> defines four macros.
2   The macro
           alignas
    expands to _Alignas; the macro
           alignof
    expands to _Alignof.
3   The remaining macros are suitable for use in #if preprocessing directives. They are
           _ _alignas_is_defined
    and
           _ _alignof_is_defined
    which both expand to the integer constant 1.

7.16 [Variable arguments ]


1   The header <stdarg.h> declares a type and defines four macros, for advancing
    through a list of arguments whose number and types are not known to the called function
    when it is translated.
2   A function may be called with a variable number of arguments of varying types. As
    described in 6.9.1, its parameter list contains one or more parameters. The rightmost
    parameter plays a special role in the access mechanism, and will be designated parmN in
    this description.
3   The type declared is
            va_list
    which is a complete object type suitable for holding information needed by the macros
    va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
    desired, the called function shall declare an object (generally referred to as ap in this
    subclause) having type va_list. The object ap may be passed as an argument to
    another function; if that function invokes the va_arg macro with parameter ap, the
    value of ap in the calling function is indeterminate and shall be passed to the va_end
    macro prior to any further reference to ap.253)
Footnote 253) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
         case the original function may make further use of the original list after the other function returns.

7.16.1 [Variable argument list access macros]


1   The va_start and va_arg macros described in this subclause shall be implemented
    as macros, not functions. It is unspecified whether va_copy and va_end are macros or
    identifiers declared with external linkage. If a macro definition is suppressed in order to
    access an actual function, or a program defines an external identifier with the same name,
    the behavior is undefined. Each invocation of the va_start and va_copy macros
    shall be matched by a corresponding invocation of the va_end macro in the same
    function.

7.16.1.1 [The va_arg macro]


1           #include <stdarg.h>
            type va_arg(va_list ap, type);
    Description
2   The va_arg macro expands to an expression that has the specified type and the value of
    the next argument in the call. The parameter ap shall have been initialized by the
    va_start or va_copy macro (without an intervening invocation of the va_end

    macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
    values of successive arguments are returned in turn. The parameter type shall be a type
    name specified such that the type of a pointer to an object that has the specified type can
    be obtained simply by postfixing a * to type. If there is no actual next argument, or if
    type is not compatible with the type of the actual next argument (as promoted according
    to the default argument promotions), the behavior is undefined, except for the following
    cases:
    -- one type is a signed integer type, the other type is the corresponding unsigned integer
       type, and the value is representable in both types;
    -- one type is pointer to void and the other is a pointer to a character type.
    Returns
3   The first invocation of the va_arg macro after that of the va_start macro returns the
    value of the argument after that specified by parmN . Successive invocations return the
    values of the remaining arguments in succession.

7.16.1.2 [The va_copy macro]


1          #include <stdarg.h>
           void va_copy(va_list dest, va_list src);
    Description
2   The va_copy macro initializes dest as a copy of src, as if the va_start macro had
    been applied to dest followed by the same sequence of uses of the va_arg macro as
    had previously been used to reach the present state of src. Neither the va_copy nor
    va_start macro shall be invoked to reinitialize dest without an intervening
    invocation of the va_end macro for the same dest.
    Returns
3   The va_copy macro returns no value.

7.16.1.3 [The va_end macro]


1          #include <stdarg.h>
           void va_end(va_list ap);
    Description
2   The va_end macro facilitates a normal return from the function whose variable
    argument list was referred to by the expansion of the va_start macro, or the function
    containing the expansion of the va_copy macro, that initialized the va_list ap. The
    va_end macro may modify ap so that it is no longer usable (without being reinitialized

    by the va_start or va_copy macro). If there is no corresponding invocation of the
    va_start or va_copy macro, or if the va_end macro is not invoked before the
    return, the behavior is undefined.
    Returns
3   The va_end macro returns no value.

7.16.1.4 [The va_start macro]


1           #include <stdarg.h>
            void va_start(va_list ap, parmN);
    Description
2   The va_start macro shall be invoked before any access to the unnamed arguments.
3   The va_start macro initializes ap for subsequent use by the va_arg and va_end
    macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
    without an intervening invocation of the va_end macro for the same ap.
4   The parameter parmN is the identifier of the rightmost parameter in the variable
    parameter list in the function definition (the one just before the , ...). If the parameter
    parmN is declared with the register storage class, with a function or array type, or
    with a type that is not compatible with the type that results after application of the default
    argument promotions, the behavior is undefined.
    Returns
5   The va_start macro returns no value.
6   EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
    more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
    pointers is specified by the first argument to f1.
            #include <stdarg.h>
            #define MAXARGS   31
            void f1(int n_ptrs, ...)
            {
                  va_list ap;
                  char *array[MAXARGS];
                  int ptr_no = 0;
                      if (n_ptrs > MAXARGS)
                            n_ptrs = MAXARGS;
                      va_start(ap, n_ptrs);
                      while (ptr_no < n_ptrs)
                            array[ptr_no++] = va_arg(ap, char *);
                      va_end(ap);
                      f2(n_ptrs, array);
             }
    Each call to f1 is required to have visible the definition of the function or a declaration such as
             void f1(int, ...);

7   EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
    indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
    is gathered again and passed to function f4.
             #include <stdarg.h>
             #define MAXARGS 31
             void f3(int n_ptrs, int f4_after, ...)
             {
                   va_list ap, ap_save;
                   char *array[MAXARGS];
                   int ptr_no = 0;
                   if (n_ptrs > MAXARGS)
                         n_ptrs = MAXARGS;
                   va_start(ap, f4_after);
                   while (ptr_no < n_ptrs) {
                         array[ptr_no++] = va_arg(ap, char *);
                         if (ptr_no == f4_after)
                               va_copy(ap_save, ap);
                   }
                   va_end(ap);
                   f2(n_ptrs, array);
                      // Now process the saved copy.
                      n_ptrs -= f4_after;
                      ptr_no = 0;
                      while (ptr_no < n_ptrs)
                            array[ptr_no++] = va_arg(ap_save, char *);
                      va_end(ap_save);
                      f4(n_ptrs, array);
             }

7.17 [Atomics ]

 Atomics 

7.17.1 [Introduction]


1   The header <stdatomic.h> defines several macros and declares several types and
    functions for performing atomic operations on data shared between threads.254)
Footnote 254) See ``future library directions'' (7.31.8).
2   Implementations that define the macro _ _STDC_NO_ATOMICS_ _ need not provide
    this header nor support any of its facilities.
3   The macros defined are the atomic lock-free macros
             ATOMIC_BOOL_LOCK_FREE
             ATOMIC_CHAR_LOCK_FREE
             ATOMIC_CHAR16_T_LOCK_FREE
             ATOMIC_CHAR32_T_LOCK_FREE
             ATOMIC_WCHAR_T_LOCK_FREE
             ATOMIC_SHORT_LOCK_FREE
             ATOMIC_INT_LOCK_FREE
             ATOMIC_LONG_LOCK_FREE
             ATOMIC_LLONG_LOCK_FREE
             ATOMIC_POINTER_LOCK_FREE
    which indicate the lock-free property of the corresponding atomic types (both signed and
    unsigned); and
             ATOMIC_FLAG_INIT
    which expands to an initializer for an object of type atomic_flag.
4   The types include
              memory_order
    which is an enumerated type whose enumerators identify memory ordering constraints;
              atomic_flag
    which is a structure type representing a lock-free, primitive atomic flag; and several 
    atomic analogs of integer types.
5   In the following synopses:
    -- An A refers to one of the atomic types.
    -- A C refers to its corresponding non-atomic type.                                        
    -- An M refers to the type of the other argument for arithmetic operations. For atomic
       integer types, M is C . For atomic pointer types, M is ptrdiff_t.

    -- The functions not ending in _explicit have the same semantics as the
       corresponding _explicit function with memory_order_seq_cst for the
       memory_order argument.
6   NOTE Many operations are volatile-qualified. The ``volatile as device register'' semantics have not
    changed in the standard. This qualification means that volatility is preserved when applying these
    operations to volatile objects.


7.17.2 [Initialization]

 Initialization

7.17.2.1 [The ATOMIC_VAR_INIT macro]


1           #include <stdatomic.h>
            #define ATOMIC_VAR_INIT(C value)
    Description
2   The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
    atomic object of a type that is initialization-compatible with value. An atomic object
    with automatic storage duration that is not explicitly initialized using
    ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
    initialization for objects with static or thread-local storage duration is guaranteed to
    produce a valid state.
3   Concurrent access to the variable being initialized, even via an atomic operation,
    constitutes a data race.
4   EXAMPLE
            atomic_int guide = ATOMIC_VAR_INIT(42);


7.17.2.2 [The atomic_init generic function]


1           #include <stdatomic.h>
            void atomic_init(volatile A *obj, C value);
    Description
2   The atomic_init generic function initializes the atomic object pointed to by obj to
    the value value, while also initializing any additional state that the implementation
    might need to carry for the atomic object.
3   Although this function initializes an atomic object, it does not avoid data races;
    concurrent access to the variable being initialized, even via an atomic operation,
    constitutes a data race.
    Returns
4   The atomic_init generic function returns no value.
5   EXAMPLE
              atomic_int guide;
              atomic_init(&guide, 42);


7.17.3 [Order and consistency]


1   The enumerated type memory_order specifies the detailed regular (non-atomic)
    memory synchronization operations as defined in 5.1.2.4 and may provide for operation
    ordering. Its enumeration constants are as follows:255)
             memory_order_relaxed
             memory_order_consume
             memory_order_acquire
             memory_order_release
             memory_order_acq_rel
             memory_order_seq_cst
Footnote 255) See ``future library directions'' (7.31.8).
2   For memory_order_relaxed, no operation orders memory.
3   For       memory_order_release,       memory_order_acq_rel,             and
    memory_order_seq_cst, a store operation performs a release operation on the
    affected memory location.
4   For       memory_order_acquire,       memory_order_acq_rel,             and
    memory_order_seq_cst, a load operation performs an acquire operation on the
    affected memory location.
5   For memory_order_consume, a load operation performs a consume operation on the
    affected memory location.
6   There shall be a single total order S on all memory_order_seq_cst operations,
    consistent with the ``happens before'' order and modification orders for all affected
    locations, such that each memory_order_seq_cst operation B that loads a value
    from an atomic object M observes one of the following values:
    -- the result of the last modification A of M that precedes B in S , if it exists, or
    -- if A exists, the result of some modification of M in the visible sequence of side
       effects with respect to B that is not memory_order_seq_cst and that does not
       happen before A, or

     -- if A does not exist, the result of some modification of M in the visible sequence of
        side effects with respect to B that is not memory_order_seq_cst.
7    NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
     an order that does include lock and unlock operations, since the ordering between those is already included
     in the ``happens before'' ordering.

8    NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
     memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic
     object be indivisible with respect to all other atomic accesses to that object.

9    For an atomic operation B that reads the value of an atomic object M , if there is a
     memory_order_seq_cst fence X sequenced before B, then B observes either the
     last memory_order_seq_cst modification of M preceding X in the total order S or
     a later modification of M in its modification order.
10   For atomic operations A and B on an atomic object M , where A modifies M and B takes
     its value, if there is a memory_order_seq_cst fence X such that A is sequenced
     before X and B follows X in S , then B observes either the effects of A or a later
     modification of M in its modification order.
11   For atomic operations A and B on an atomic object M , where A modifies M and B takes
     its value, if there are memory_order_seq_cst fences X and Y such that A is
     sequenced before X , Y is sequenced before B, and X precedes Y in S , then B observes
     either the effects of A or a later modification of M in its modification order.
12   Atomic read-modify-write operations shall always read the last value (in the modification
     order) stored before the write associated with the read-modify-write operation.
13   An atomic store shall only store a value that has been computed from constants and
     program input values by a finite sequence of program evaluations, such that each
     evaluation observes the values of variables as computed by the last prior assignment in
     the sequence.256) The ordering of evaluations in this sequence shall be such that
     -- If an evaluation B observes a value computed by A in a different thread, then B does
        not happen before A.
     -- If an evaluation A is included in the sequence, then all evaluations that assign to the
        same variable and happen before A are also included.
Footnote 256) Among other implications, atomic variables shall not decay.
14   NOTE 3 The second requirement disallows ``out-of-thin-air'', or ``speculative'' stores of atomics when
     relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
     sequence out of thread order. For example, with x and y initially zero,

               // Thread 1:
               r1 = atomic_load_explicit(&y, memory_order_relaxed);
               atomic_store_explicit(&x, r1, memory_order_relaxed);

               // Thread 2:
               r2 = atomic_load_explicit(&x, memory_order_relaxed);
               atomic_store_explicit(&y, 42, memory_order_relaxed);
     is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:
               atomic_store_explicit(&y, 42,             memory_order_relaxed);
               r1 = atomic_load_explicit(&y,             memory_order_relaxed);
               atomic_store_explicit(&x, r1,             memory_order_relaxed);
               r2 = atomic_load_explicit(&x,             memory_order_relaxed);
     On the other hand,
               // Thread 1:
               r1 = atomic_load_explicit(&y, memory_order_relaxed);
               atomic_store_explicit(&x, r1, memory_order_relaxed);

               // Thread 2:
               r2 = atomic_load_explicit(&x, memory_order_relaxed);
               atomic_store_explicit(&y, r2, memory_order_relaxed);
     is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
     in the computation of 42. In the absence of ``relaxed'' operations and read-modify-write operations with
     weaker than memory_order_acq_rel ordering, the second requirement has no impact.

     Recommended practice
15   The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
     with x and y initially zero:
             // Thread 1:
             r1 = atomic_load_explicit(&x, memory_order_relaxed);
             if (r1 == 42)
                  atomic_store_explicit(&y, r1, memory_order_relaxed);

             // Thread 2:
             r2 = atomic_load_explicit(&y, memory_order_relaxed);
             if (r2 == 42)
                  atomic_store_explicit(&x, 42, memory_order_relaxed);
     However, this is not useful behavior, and implementations should not allow it.
16   Implementations should make atomic stores visible to atomic loads within a reasonable
     amount of time.

7.17.3.1 [The kill_dependency macro]


1          #include <stdatomic.h>
           type kill_dependency(type y);
    Description
2   The kill_dependency macro terminates a dependency chain; the argument does not
    carry a dependency to the return value.
    Returns
3   The kill_dependency macro returns the value of y.

7.17.4 [Fences]


1   This subclause introduces synchronization primitives called fences. Fences can have
    acquire semantics, release semantics, or both. A fence with acquire semantics is called
    an acquire fence; a fence with release semantics is called a release fence.
2   A release fence A synchronizes with an acquire fence B if there exist atomic operations
    X and Y , both operating on some atomic object M , such that A is sequenced before X , X
    modifies M , Y is sequenced before B, and Y reads the value written by X or a value
    written by any side effect in the hypothetical release sequence X would head if it were a
    release operation.
3   A release fence A synchronizes with an atomic operation B that performs an acquire
    operation on an atomic object M if there exists an atomic operation X such that A is
    sequenced before X , X modifies M , and B reads the value written by X or a value written
    by any side effect in the hypothetical release sequence X would head if it were a release
    operation.
4   An atomic operation A that is a release operation on an atomic object M synchronizes
    with an acquire fence B if there exists some atomic operation X on M such that X is
    sequenced before B and reads the value written by A or a value written by any side effect
    in the release sequence headed by A.

7.17.4.1 [The atomic_thread_fence function]


1          #include <stdatomic.h>
           void atomic_thread_fence(memory_order order);
    Description
2   Depending on the value of order, this operation:
    -- has no effects, if order == memory_order_relaxed;

    -- is an acquire fence, if order == memory_order_acquire or order ==
       memory_order_consume;
    -- is a release fence, if order == memory_order_release;
    -- is both an acquire fence                   and     a    release    fence,     if   order        ==
       memory_order_acq_rel;
    -- is a sequentially consistent acquire and release fence, if order                                ==
       memory_order_seq_cst.
    Returns
3   The atomic_thread_fence function returns no value.

7.17.4.2 [The atomic_signal_fence function]


1           #include <stdatomic.h>
            void atomic_signal_fence(memory_order order);
    Description
2   Equivalent to atomic_thread_fence(order), except that the resulting ordering
    constraints are established only between a thread and a signal handler executed in the
    same thread.
3   NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
    performed by the thread become visible to the signal handler.

4   NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
    atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
    have inserted are not emitted.

    Returns
5   The atomic_signal_fence function returns no value.

7.17.5 [Lock-free property]


1   The atomic lock-free macros indicate the lock-free property of integer and address atomic
    types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
    the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
2   NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
    memory location via two different addresses will communicate atomically. The implementation should not
    depend on any per-process state. This restriction enables communication via memory mapped into a
    process more than once and memory shared between two processes.

7.17.5.1 [The atomic_is_lock_free generic function]


1            #include <stdatomic.h>
             _Bool atomic_is_lock_free(const volatile A *obj);
    Description
2   The atomic_is_lock_free generic function indicates whether or not the object
    pointed to by obj is lock-free.                                              
    Returns
3   The atomic_is_lock_free generic function returns nonzero (true) if and only if the
    object's operations are lock-free. The result of a lock-free query on one object cannot be
    inferred from the result of a lock-free query on another object.

7.17.6 [Atomic integer types]


1   For each line in the following table,257) the atomic type name is declared as a type that
    has the same representation and alignment requirements as the corresponding direct
    type.258)

                  Atomic type name                            Direct type
              atomic_bool                        _Atomic     _Bool
              atomic_char                        _Atomic     char
              atomic_schar                       _Atomic     signed char
              atomic_uchar                       _Atomic     unsigned char
              atomic_short                       _Atomic     short
              atomic_ushort                      _Atomic     unsigned short
              atomic_int                         _Atomic     int
              atomic_uint                        _Atomic     unsigned int
              atomic_long                        _Atomic     long
              atomic_ulong                       _Atomic     unsigned long
              atomic_llong                       _Atomic     long long
              atomic_ullong                      _Atomic     unsigned long long
              atomic_char16_t                    _Atomic     char16_t
              atomic_char32_t                    _Atomic     char32_t
              atomic_wchar_t                     _Atomic     wchar_t
              atomic_int_least8_t                _Atomic     int_least8_t
              atomic_uint_least8_t               _Atomic     uint_least8_t
              atomic_int_least16_t               _Atomic     int_least16_t
              atomic_uint_least16_t              _Atomic     uint_least16_t
              atomic_int_least32_t               _Atomic     int_least32_t
              atomic_uint_least32_t              _Atomic     uint_least32_t
              atomic_int_least64_t               _Atomic     int_least64_t
              atomic_uint_least64_t              _Atomic     uint_least64_t
              atomic_int_fast8_t                 _Atomic     int_fast8_t
              atomic_uint_fast8_t                _Atomic     uint_fast8_t
              atomic_int_fast16_t                _Atomic     int_fast16_t
              atomic_uint_fast16_t               _Atomic     uint_fast16_t
              atomic_int_fast32_t                _Atomic     int_fast32_t
              atomic_uint_fast32_t               _Atomic     uint_fast32_t
              atomic_int_fast64_t                _Atomic     int_fast64_t
              atomic_uint_fast64_t               _Atomic     uint_fast64_t
              atomic_intptr_t                    _Atomic     intptr_t
              atomic_uintptr_t                   _Atomic     uintptr_t
              atomic_size_t                      _Atomic     size_t
              atomic_ptrdiff_t                   _Atomic     ptrdiff_t
              atomic_intmax_t                    _Atomic     intmax_t
              atomic_uintmax_t                   _Atomic     uintmax_t
Footnote 257) See ``future library directions'' (7.31.8).
Footnote 258) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.
2   The semantics of the operations on these types are defined in 7.17.7.                       

3   NOTE The representation of atomic integer types need not have the same size as their corresponding
    regular types. They should have the same size whenever possible, as it eases effort required to port existing
    code.


7.17.7 [Operations on atomic types]


1   There are only a few kinds of operations on atomic types, though there are many
    instances of those kinds. This subclause specifies each general kind.

7.17.7.1 [The atomic_store generic functions]


1            #include <stdatomic.h>
             void atomic_store(volatile A *object, C desired);
             void atomic_store_explicit(volatile A *object,
                  C desired, memory_order order);
    Description
2   The      order      argument    shall    not    be    memory_order_acquire,
    memory_order_consume, nor memory_order_acq_rel. Atomically replace the
    value pointed to by object with the value of desired. Memory is affected according
    to the value of order.
    Returns
3   The atomic_store generic functions return no value.

7.17.7.2 [The atomic_load generic functions]


1            #include <stdatomic.h>
             C atomic_load(volatile A *object);
             C atomic_load_explicit(volatile A *object,
                  memory_order order);
    Description
2   The order argument shall not be memory_order_release nor
    memory_order_acq_rel. Memory is affected according to the value of order.
    Returns
    Atomically returns the value pointed to by object.

7.17.7.3 [The atomic_exchange generic functions]


1            #include <stdatomic.h>
             C atomic_exchange(volatile A *object, C desired);
             C atomic_exchange_explicit(volatile A *object,
                  C desired, memory_order order);
    Description
2   Atomically replace the value pointed to by object with desired. Memory is affected
    according to the value of order. These operations are read-modify-write operations
    (5.1.2.4).
    Returns
3   Atomically returns the value pointed to by object immediately before the effects.

7.17.7.4 [The atomic_compare_exchange generic functions]


1            #include <stdatomic.h>
             _Bool atomic_compare_exchange_strong(volatile A *object,
                  C *expected, C desired);
             _Bool atomic_compare_exchange_strong_explicit(
                  volatile A *object, C *expected, C desired,
                  memory_order success, memory_order failure);
             _Bool atomic_compare_exchange_weak(volatile A *object,
                  C *expected, C desired);
             _Bool atomic_compare_exchange_weak_explicit(
                  volatile A *object, C *expected, C desired,
                  memory_order success, memory_order failure);
    Description
2   The failure argument shall not be memory_order_release nor
    memory_order_acq_rel. The failure argument shall be no stronger than the
    success argument. Atomically, compares the value pointed to by object for equality
    with that in expected, and if true, replaces the value pointed to by object with
    desired, and if false, updates the value in expected with the value pointed to by
    object. Further, if the comparison is true, memory is affected according to the value of
    success, and if the comparison is false, memory is affected according to the value of
    failure. These operations are atomic read-modify-write operations (5.1.2.4).
3   NOTE 1    For example, the effect of atomic_compare_exchange_strong is
             if (memcmp(object, expected, sizeof (*object)) == 0)
                   memcpy(object, &desired, sizeof (*object));
             else
                   memcpy(expected, object, sizeof (*object));

4   A weak compare-and-exchange operation may fail spuriously. That is, even when the
    contents of memory referred to by expected and object are equal, it may return zero
    and store back to expected the same memory contents that were originally there.
5   NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
    machines, e.g. load-locked store-conditional machines.

6   EXAMPLE         A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
    be in a loop.
             exp = atomic_load(&cur);
             do {
                   des = function(exp);
             } while (!atomic_compare_exchange_weak(&cur, &exp, des));
    When a compare-and-exchange is in a loop, the weak version will yield better performance on some
    platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
    strong one is preferable.

    Returns
7   The result of the comparison.

7.17.7.5 [The atomic_fetch and modify generic functions]


1   The following operations perform arithmetic and bitwise computations. All of these
    operations are applicable to an object of any atomic integer type. None of these 
    operations is applicable to atomic_bool. The key, operator, and computation
    correspondence is:
     key            op          computation
     add            +       addition
     sub            -       subtraction
     or             |       bitwise inclusive or
     xor            ^       bitwise exclusive or
     and            &       bitwise and
    Synopsis
2            #include <stdatomic.h>
             C atomic_fetch_key(volatile A *object, M operand);
             C atomic_fetch_key_explicit(volatile A *object,
                  M operand, memory_order order);
    Description
3   Atomically replaces the value pointed to by object with the result of the computation
    applied to the value pointed to by object and the given operand. Memory is affected
    according to the value of order. These operations are atomic read-modify-write
    operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's
    complement representation with silent wrap-around on overflow; there are no undefined
    results. For address types, the result may be an undefined address, but the operations
    otherwise have no undefined behavior.
    Returns
4   Atomically, the value pointed to by object immediately before the effects.
5   NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
    operation of the corresponding op= compound assignment operators. The only differences are that the
    compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
    compound assignment operator is the updated value of the object, whereas the value returned by the
    atomic_fetch and modify generic functions is the previous value of the atomic object.


7.17.8 [Atomic flag type and operations]


1   The atomic_flag type provides the classic test-and-set functionality. It has two
    states, set and clear.
2   Operations on an object of type atomic_flag shall be lock free.
3   NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
    the atomic_flag type is the minimum hardware-implemented type needed to conform to this
    International standard. The remaining types can be emulated with atomic_flag, though with less than
    ideal properties.

4   The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
    clear state. An atomic_flag that is not explicitly initialized with
    ATOMIC_FLAG_INIT is initially in an indeterminate state.
5   EXAMPLE
            atomic_flag guard = ATOMIC_FLAG_INIT;


7.17.8.1 [The atomic_flag_test_and_set functions]


1           #include <stdatomic.h>
            _Bool atomic_flag_test_and_set(
                 volatile atomic_flag *object);
            _Bool atomic_flag_test_and_set_explicit(
                 volatile atomic_flag *object, memory_order order);
    Description
2   Atomically sets the value pointed to by object to true. Memory is affected according
    to the value of order. These operations are atomic read-modify-write operations
    (5.1.2.4).
    Returns
3   Atomically, the value of the object immediately before the effects.

7.17.8.2 [The atomic_flag_clear functions]


1          #include <stdatomic.h>
           void atomic_flag_clear(volatile atomic_flag *object);
           void atomic_flag_clear_explicit(
                volatile atomic_flag *object, memory_order order);
    Description
2   The order argument shall not be memory_order_acquire nor
    memory_order_acq_rel. Atomically sets the value pointed to by object to false.
    Memory is affected according to the value of order.
    Returns
3   The atomic_flag_clear functions return no value.

7.18 [Boolean type and values ]


1   The header <stdbool.h> defines four macros.
2   The macro
             bool
    expands to _Bool.
3   The remaining three macros are suitable for use in #if preprocessing directives. They
    are
             true
    which expands to the integer constant 1,
             false
    which expands to the integer constant 0, and
             _ _bool_true_false_are_defined
    which expands to the integer constant 1.
4   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
    redefine the macros bool, true, and false.259)

Footnote 259) See ``future library directions'' (7.31.9).

7.19 [Common definitions ]


1   The header <stddef.h> defines the following macros and declares the following types.
    Some are also defined in other headers, as noted in their respective subclauses.
2   The types are
           ptrdiff_t
    which is the signed integer type of the result of subtracting two pointers;
           size_t
    which is the unsigned integer type of the result of the sizeof operator;
           max_align_t
    which is an object type whose alignment is as great as is supported by the implementation
    in all contexts; and
           wchar_t
    which is an integer type whose range of values can represent distinct codes for all
    members of the largest extended character set specified among the supported locales; the
    null character shall have the code value zero. Each member of the basic character set
    shall have a code value equal to its value when used as the lone character in an integer
    character      constant     if     an      implementation      does      not      define
    _ _STDC_MB_MIGHT_NEQ_WC_ _.
3   The macros are
           NULL
    which expands to an implementation-defined null pointer constant; and
           offsetof(type, member-designator)
    which expands to an integer constant expression that has type size_t, the value of
    which is the offset in bytes, to the structure member (designated by member-designator ),
    from the beginning of its structure (designated by type). The type and member designator
    shall be such that given
           static type t;
    then the expression &(t.member-designator) evaluates to an address constant. (If the
    specified member is a bit-field, the behavior is undefined.)
    Recommended practice
4   The types used for size_t and ptrdiff_t should not have an integer conversion rank
    greater than that of signed long int unless the implementation supports objects
    large enough to make this necessary.                                               


7.20 [Integer types ]


1   The header <stdint.h> declares sets of integer types having specified widths, and
    defines corresponding sets of macros.260) It also defines macros that specify limits of
    integer types corresponding to types defined in other standard headers.
Footnote 260) See ``future library directions'' (7.31.10).
2   Types are defined in the following categories:
    -- integer types having certain exact widths;
    -- integer types having at least certain specified widths;
    -- fastest integer types having at least certain specified widths;
    -- integer types wide enough to hold pointers to objects;
    -- integer types having greatest width.
    (Some of these types may denote the same type.)
3   Corresponding macros specify limits of the declared types and construct suitable
    constants.
4   For each type described herein that the implementation provides,261) <stdint.h> shall
    declare that typedef name and define the associated macros. Conversely, for each type
    described herein that the implementation does not provide, <stdint.h> shall not
    declare that typedef name nor shall it define the associated macros. An implementation
    shall provide those types described as ``required'', but need not provide any of the others
    (described as ``optional'').
Footnote 261) Some of these types may denote implementation-defined extended integer types.

7.20.1 [Integer types]


1   When typedef names differing only in the absence or presence of the initial u are defined,
    they shall denote corresponding signed and unsigned types as described in 6.2.5; an
    implementation providing one of these corresponding types shall also provide the other.
2   In the following descriptions, the symbol N represents an unsigned decimal integer with
    no leading zeros (e.g., 8 or 24, but not 04 or 048).


7.20.1.1 [Exact-width integer types]


1   The typedef name intN_t designates a signed integer type with width N , no padding
    bits, and a two's complement representation. Thus, int8_t denotes such a signed
    integer type with a width of exactly 8 bits.
2   The typedef name uintN_t designates an unsigned integer type with width N and no
    padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
    exactly 24 bits.
3   These types are optional. However, if an implementation provides integer types with
    widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
    two's complement representation, it shall define the corresponding typedef names.

7.20.1.2 [Minimum-width integer types]


1   The typedef name int_leastN_t designates a signed integer type with a width of at
    least N , such that no signed integer type with lesser size has at least the specified width.
    Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
2   The typedef name uint_leastN_t designates an unsigned integer type with a width
    of at least N , such that no unsigned integer type with lesser size has at least the specified
    width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
    least 16 bits.
3   The following types are required:
             int_least8_t                                      uint_least8_t
             int_least16_t                                     uint_least16_t
             int_least32_t                                     uint_least32_t
             int_least64_t                                     uint_least64_t
    All other types of this form are optional.

7.20.1.3 [Fastest minimum-width integer types]


1   Each of the following types designates an integer type that is usually fastest262) to operate
    with among all integer types that have at least the specified width.
Footnote 262) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
         grounds for choosing one type over another, it will simply pick some integer type satisfying the
         signedness and width requirements.
2   The typedef name int_fastN_t designates the fastest signed integer type with a width
    of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
    type with a width of at least N .

3   The following types are required:
            int_fast8_t                                    uint_fast8_t
            int_fast16_t                                   uint_fast16_t
            int_fast32_t                                   uint_fast32_t
            int_fast64_t                                   uint_fast64_t
    All other types of this form are optional.

7.20.1.4 [Integer types capable of holding object pointers]


1   The following type designates a signed integer type with the property that any valid
    pointer to void can be converted to this type, then converted back to pointer to void,
    and the result will compare equal to the original pointer:
            intptr_t
    The following type designates an unsigned integer type with the property that any valid
    pointer to void can be converted to this type, then converted back to pointer to void,
    and the result will compare equal to the original pointer:
            uintptr_t
    These types are optional.

7.20.1.5 [Greatest-width integer types]


1   The following type designates a signed integer type capable of representing any value of
    any signed integer type:
            intmax_t
    The following type designates an unsigned integer type capable of representing any value
    of any unsigned integer type:
            uintmax_t
    These types are required.

7.20.2 [Limits of specified-width integer types]


1   The following object-like macros specify the minimum and maximum limits of the types
    declared in <stdint.h>. Each macro name corresponds to a similar type name in 7.20.1.
2   Each instance of any defined macro shall be replaced by a constant expression suitable
    for use in #if preprocessing directives, and this expression shall have the same type as
    would an expression that is an object of the corresponding type converted according to
    the integer promotions. Its implementation-defined value shall be equal to or greater in
    magnitude (absolute value) than the corresponding value given below, with the same sign,
    except where stated to be exactly the given value.


7.20.2.1 [Limits of exact-width integer types]


1   -- minimum values of exact-width signed integer types
          INTN_MIN                                   exactly -(2 N -1 )
    -- maximum values of exact-width signed integer types
          INTN_MAX                                   exactly 2 N -1 - 1
    -- maximum values of exact-width unsigned integer types
       UINTN_MAX                                     exactly 2 N - 1

7.20.2.2 [Limits of minimum-width integer types]


1   -- minimum values of minimum-width signed integer types
          INT_LEASTN_MIN                                     -(2 N -1 - 1)
    -- maximum values of minimum-width signed integer types
          INT_LEASTN_MAX                                     2 N -1 - 1
    -- maximum values of minimum-width unsigned integer types
       UINT_LEASTN_MAX                                       2N - 1

7.20.2.3 [Limits of fastest minimum-width integer types]


1   -- minimum values of fastest minimum-width signed integer types
          INT_FASTN_MIN                                      -(2 N -1 - 1)
    -- maximum values of fastest minimum-width signed integer types
       INT_FASTN_MAX                                         2 N -1 - 1
    -- maximum values of fastest minimum-width unsigned integer types
       UINT_FASTN_MAX                                        2N - 1

7.20.2.4 [Limits of integer types capable of holding object pointers]


1   -- minimum value of pointer-holding signed integer type
          INTPTR_MIN                                         -(215 - 1)
    -- maximum value of pointer-holding signed integer type
       INTPTR_MAX                                            215 - 1
    -- maximum value of pointer-holding unsigned integer type
       UINTPTR_MAX                                           216 - 1


7.20.2.5 [Limits of greatest-width integer types]


1   -- minimum value of greatest-width signed integer type
        INTMAX_MIN                                                    -(263 - 1)
    -- maximum value of greatest-width signed integer type
        INTMAX_MAX                                                    263 - 1
    -- maximum value of greatest-width unsigned integer type
        UINTMAX_MAX                                                   264 - 1

7.20.3 [Limits of other integer types]


1   The following object-like macros specify the minimum and maximum limits of integer
    types corresponding to types defined in other standard headers.
2   Each instance of these macros shall be replaced by a constant expression suitable for use
    in #if preprocessing directives, and this expression shall have the same type as would an
    expression that is an object of the corresponding type converted according to the integer
    promotions. Its implementation-defined value shall be equal to or greater in magnitude
    (absolute value) than the corresponding value given below, with the same sign. An
    implementation shall define only the macros corresponding to those typedef names it
    actually provides.263)
    -- limits of ptrdiff_t
        PTRDIFF_MIN                                                 -65535
        PTRDIFF_MAX                                                 +65535
    -- limits of sig_atomic_t
        SIG_ATOMIC_MIN                                              see below
        SIG_ATOMIC_MAX                                              see below
    -- limit of size_t
        SIZE_MAX                                                      65535
    -- limits of wchar_t
        WCHAR_MIN                                                   see below
        WCHAR_MAX                                                   see below
    -- limits of wint_t

        WINT_MIN                                              see below
        WINT_MAX                                              see below
Footnote 263) A freestanding implementation need not provide all of these types.
3   If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
    SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
    shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
    type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
    SIG_ATOMIC_MAX shall be no less than 255.
4   If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
    shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
    otherwise, wchar_t is defined as an unsigned integer type, and the value of
    WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.264)
Footnote 264) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
         character set.
5   If wint_t (see 7.29) is defined as a signed integer type, the value of WINT_MIN shall
    be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
    otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
    shall be 0 and the value of WINT_MAX shall be no less than 65535.

7.20.4 [Macros for integer constants]


1   The following function-like macros expand to integer constants suitable for initializing
    objects that have integer types corresponding to types defined in <stdint.h>. Each
    macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
2   The argument in any instance of these macros shall be an unsuffixed integer constant (as
    defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
3   Each invocation of one of these macros shall expand to an integer constant expression
    suitable for use in #if preprocessing directives. The type of the expression shall have
    the same type as would an expression of the corresponding type converted according to
    the integer promotions. The value of the expression shall be that of the argument.

7.20.4.1 [Macros for minimum-width integer constants]


1   The macro INTN_C(value) shall expand to an integer constant expression
    corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
    to an integer constant expression corresponding to the type uint_leastN_t. For
    example, if uint_least64_t is a name for the type unsigned long long int,
    then UINT64_C(0x123) might expand to the integer constant 0x123ULL.


7.20.4.2 [Macros for greatest-width integer constants]


1   The following macro expands to an integer constant expression having the value specified
    by its argument and the type intmax_t:
            INTMAX_C(value)
    The following macro expands to an integer constant expression having the value specified
    by its argument and the type uintmax_t:
            UINTMAX_C(value)

7.21 [Input/output ]

 Input/output 

7.21.1 [Introduction]


1   The header <stdio.h> defines several macros, and declares three types and many
    functions for performing input and output.
2   The types declared are size_t (described in 7.19);
           FILE
    which is an object type capable of recording all the information needed to control a
    stream, including its file position indicator, a pointer to its associated buffer (if any), an
    error indicator that records whether a read/write error has occurred, and an end-of-file
    indicator that records whether the end of the file has been reached; and
           fpos_t
    which is a complete object type other than an array type capable of recording all the
    information needed to specify uniquely every position within a file.
3   The macros are NULL (described in 7.19);
           _IOFBF
           _IOLBF
           _IONBF
    which expand to integer constant expressions with distinct values, suitable for use as the
    third argument to the setvbuf function;
           BUFSIZ
    which expands to an integer constant expression that is the size of the buffer used by the
    setbuf function;
           EOF
    which expands to an integer constant expression, with type int and a negative value, that
    is returned by several functions to indicate end-of-file, that is, no more input from a
    stream;
           FOPEN_MAX
    which expands to an integer constant expression that is the minimum number of files that
    the implementation guarantees can be open simultaneously;
           FILENAME_MAX
    which expands to an integer constant expression that is the size needed for an array of
    char large enough to hold the longest file name string that the implementation

    guarantees can be opened;265)
             L_tmpnam
    which expands to an integer constant expression that is the size needed for an array of
    char large enough to hold a temporary file name string generated by the tmpnam
    function;
             SEEK_CUR
             SEEK_END
             SEEK_SET
    which expand to integer constant expressions with distinct values, suitable for use as the
    third argument to the fseek function;
             TMP_MAX
    which expands to an integer constant expression that is the minimum number of unique
    file names that can be generated by the tmpnam function;
             stderr
             stdin
             stdout
    which are expressions of type ``pointer to FILE'' that point to the FILE objects
    associated, respectively, with the standard error, input, and output streams.
Footnote 265) If the implementation imposes no practical limit on the length of file name strings, the value of
         FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
         string. Of course, file name string contents are subject to other system-specific constraints; therefore
         all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.
4   The header <wchar.h> declares a number of functions useful for wide character input
    and output. The wide character input/output functions described in that subclause
    provide operations analogous to most of those described here, except that the
    fundamental units internal to the program are wide characters. The external
    representation (in the file) is a sequence of ``generalized'' multibyte characters, as
    described further in 7.21.3.
5   The input/output functions are given the following collective terms:
    -- The wide character input functions -- those functions described in 7.29 that perform
       input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
       fwscanf, wscanf, vfwscanf, and vwscanf.
    -- The wide character output functions -- those functions described in 7.29 that perform
       output from wide characters and wide strings: fputwc, fputws, putwc,
       putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.

    -- The wide character input/output functions -- the union of the ungetwc function, the
       wide character input functions, and the wide character output functions.
    -- The byte input/output functions -- those functions described in this subclause that
       perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
       fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf,
       ungetc, vfprintf, vfscanf, vprintf, and vscanf.
    Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
    tmpnam function (7.21.4.4), <wchar.h> (7.29).

7.21.2 [Streams]


1   Input and output, whether to or from physical devices such as terminals and tape drives,
    or whether to or from files supported on structured storage devices, are mapped into
    logical data streams, whose properties are more uniform than their various inputs and
    outputs. Two forms of mapping are supported, for text streams and for binary
    streams.266)
Footnote 266) An implementation need not distinguish between text streams and binary streams. In such an
         implementation, there need be no new-line characters in a text stream nor any limit to the length of a
         line.
2   A text stream is an ordered sequence of characters composed into lines, each line
    consisting of zero or more characters plus a terminating new-line character. Whether the
    last line requires a terminating new-line character is implementation-defined. Characters
    may have to be added, altered, or deleted on input and output to conform to differing
    conventions for representing text in the host environment. Thus, there need not be a one-
    to-one correspondence between the characters in a stream and those in the external
    representation. Data read in from a text stream will necessarily compare equal to the data
    that were earlier written out to that stream only if: the data consist only of printing
    characters and the control characters horizontal tab and new-line; no new-line character is
    immediately preceded by space characters; and the last character is a new-line character.
    Whether space characters that are written out immediately before a new-line character
    appear when read in is implementation-defined.
3   A binary stream is an ordered sequence of characters that can transparently record
    internal data. Data read in from a binary stream shall compare equal to the data that were
    earlier written out to that stream, under the same implementation. Such a stream may,
    however, have an implementation-defined number of null characters appended to the end
    of the stream.
4   Each stream has an orientation. After a stream is associated with an external file, but
    before any operations are performed on it, the stream is without orientation. Once a wide
    character input/output function has been applied to a stream without orientation, the

    stream becomes a wide-oriented stream . Similarly, once a byte input/output function has
    been applied to a stream without orientation, the stream becomes a byte-oriented stream .
    Only a call to the freopen function or the fwide function can otherwise alter the
    orientation of a stream. (A successful call to freopen removes any orientation.)267)
Footnote 267) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.
5   Byte input/output functions shall not be applied to a wide-oriented stream and wide
    character input/output functions shall not be applied to a byte-oriented stream. The
    remaining stream operations do not affect, and are not affected by, a stream's orientation,
    except for the following additional restrictions:
    -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
       text and binary streams.
    -- For wide-oriented streams, after a successful call to a file-positioning function that
       leaves the file position indicator prior to the end-of-file, a wide character output
       function can overwrite a partial multibyte character; any file contents beyond the
       byte(s) written are henceforth indeterminate.
6   Each wide-oriented stream has an associated mbstate_t object that stores the current
    parse state of the stream. A successful call to fgetpos stores a representation of the
    value of this mbstate_t object as part of the value of the fpos_t object. A later
    successful call to fsetpos using the same stored fpos_t value restores the value of
    the associated mbstate_t object as well as the position within the controlled stream.
7   Each stream has an associated lock that is used to prevent data races when multiple
    threads of execution access a stream, and to restrict the interleaving of stream operations
    performed by multiple threads. Only one thread may hold this lock at a time. The lock is
    reentrant: a single thread may hold the lock multiple times at a given time.
8   All functions that read, write, position, or query the position of a stream lock the stream
    before accessing it. They release the lock associated with the stream when the access is
    complete.
    Environmental limits
9   An implementation shall support text files with lines containing at least 254 characters,
    including the terminating new-line character. The value of the macro BUFSIZ shall be at
    least 256.
    Forward references: the freopen function (7.21.5.4), the fwide function (7.29.3.5),
    mbstate_t (7.30.1), the fgetpos function (7.21.9.1), the fsetpos function
    (7.21.9.3).


7.21.3 [Files]


1   A stream is associated with an external file (which may be a physical device) by opening
    a file, which may involve creating a new file. Creating an existing file causes its former
    contents to be discarded, if necessary. If a file can support positioning requests (such as a
    disk file, as opposed to a terminal), then a file position indicator associated with the
    stream is positioned at the start (character number zero) of the file, unless the file is
    opened with append mode in which case it is implementation-defined whether the file
    position indicator is initially positioned at the beginning or the end of the file. The file
    position indicator is maintained by subsequent reads, writes, and positioning requests, to
    facilitate an orderly progression through the file.
2   Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
    stream causes the associated file to be truncated beyond that point is implementation-
    defined.
3   When a stream is unbuffered , characters are intended to appear from the source or at the
    destination as soon as possible. Otherwise characters may be accumulated and
    transmitted to or from the host environment as a block. When a stream is fully buffered ,
    characters are intended to be transmitted to or from the host environment as a block when
    a buffer is filled. When a stream is line buffered , characters are intended to be
    transmitted to or from the host environment as a block when a new-line character is
    encountered. Furthermore, characters are intended to be transmitted as a block to the host
    environment when a buffer is filled, when input is requested on an unbuffered stream, or
    when input is requested on a line buffered stream that requires the transmission of
    characters from the host environment. Support for these characteristics is
    implementation-defined, and may be affected via the setbuf and setvbuf functions.
4   A file may be disassociated from a controlling stream by closing the file. Output streams
    are flushed (any unwritten buffer contents are transmitted to the host environment) before
    the stream is disassociated from the file. The value of a pointer to a FILE object is
    indeterminate after the associated file is closed (including the standard text streams).
    Whether a file of zero length (on which no characters have been written by an output
    stream) actually exists is implementation-defined.
5   The file may be subsequently reopened, by the same or another program execution, and
    its contents reclaimed or modified (if it can be repositioned at its start). If the main
    function returns to its original caller, or if the exit function is called, all open files are
    closed (hence all output streams are flushed) before program termination. Other paths to
    program termination, such as calling the abort function, need not close all files
    properly.
6   The address of the FILE object used to control a stream may be significant; a copy of a
    FILE object need not serve in place of the original.

7    At program startup, three text streams are predefined and need not be opened explicitly
     -- standard input (for reading conventional input), standard output (for writing
     conventional output), and standard error (for writing diagnostic output). As initially
     opened, the standard error stream is not fully buffered; the standard input and standard
     output streams are fully buffered if and only if the stream can be determined not to refer
     to an interactive device.
8    Functions that open additional (nontemporary) files require a file name, which is a string.
     The rules for composing valid file names are implementation-defined. Whether the same
     file can be simultaneously open multiple times is also implementation-defined.
9    Although both text and binary wide-oriented streams are conceptually sequences of wide
     characters, the external file associated with a wide-oriented stream is a sequence of
     multibyte characters, generalized as follows:
     -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
        encodings valid for use internal to the program).
     -- A file need not begin nor end in the initial shift state.268)
Footnote 268) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
          undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
          with state-dependent encoding that does not assuredly end in the initial shift state.
10   Moreover, the encodings used for multibyte characters may differ among files. Both the
     nature and choice of such encodings are implementation-defined.
11   The wide character input functions read multibyte characters from the stream and convert
     them to wide characters as if they were read by successive calls to the fgetwc function.
     Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
     described by the stream's own mbstate_t object. The byte input functions read
     characters from the stream as if by successive calls to the fgetc function.
12   The wide character output functions convert wide characters to multibyte characters and
     write them to the stream as if they were written by successive calls to the fputwc
     function. Each conversion occurs as if by a call to the wcrtomb function, with the
     conversion state described by the stream's own mbstate_t object. The byte output
     functions write characters to the stream as if by successive calls to the fputc function.
13   In some cases, some of the byte input/output functions also perform conversions between
     multibyte characters and wide characters. These conversions also occur as if by calls to
     the mbrtowc and wcrtomb functions.
14   An encoding error occurs if the character sequence presented to the underlying
     mbrtowc function does not form a valid (generalized) multibyte character, or if the code
     value passed to the underlying wcrtomb does not correspond to a valid (generalized)

     multibyte character. The wide character input/output functions and the byte input/output
     functions store the value of the macro EILSEQ in errno if and only if an encoding error
     occurs.
     Environmental limits
15   The value of FOPEN_MAX shall be at least eight, including the three standard text
     streams.
     Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
     fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
     (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.29.3.1), the
     fputwc function (7.29.3.3), conversion state (7.29.6), the mbrtowc function
     (7.29.6.3.2), the wcrtomb function (7.29.6.3.3).

7.21.4 [Operations on files]

 Operations on files

7.21.4.1 [The remove function]


1           #include <stdio.h>
            int remove(const char *filename);
     Description
2    The remove function causes the file whose name is the string pointed to by filename
     to be no longer accessible by that name. A subsequent attempt to open that file using that
     name will fail, unless it is created anew. If the file is open, the behavior of the remove
     function is implementation-defined.
     Returns
3    The remove function returns zero if the operation succeeds, nonzero if it fails.

7.21.4.2 [The rename function]


1           #include <stdio.h>
            int rename(const char *old, const char *new);
     Description
2    The rename function causes the file whose name is the string pointed to by old to be
     henceforth known by the name given by the string pointed to by new. The file named
     old is no longer accessible by that name. If a file named by the string pointed to by new
     exists prior to the call to the rename function, the behavior is implementation-defined.
    Returns
3   The rename function returns zero if the operation succeeds, nonzero if it fails,269) in
    which case if the file existed previously it is still known by its original name.
Footnote 269) Among the reasons the implementation may cause the rename function to fail are that the file is open
         or that it is necessary to copy its contents to effectuate its renaming.

7.21.4.3 [The tmpfile function]


1           #include <stdio.h>
            FILE *tmpfile(void);
    Description
2   The tmpfile function creates a temporary binary file that is different from any other
    existing file and that will automatically be removed when it is closed or at program
    termination. If the program terminates abnormally, whether an open temporary file is
    removed is implementation-defined. The file is opened for update with "wb+" mode.
    Recommended practice
3   It should be possible to open at least TMP_MAX temporary files during the lifetime of the
    program (this limit may be shared with tmpnam) and there should be no limit on the
    number simultaneously open other than this limit and any limit on the number of open
    files (FOPEN_MAX).
    Returns
4   The tmpfile function returns a pointer to the stream of the file that it created. If the file
    cannot be created, the tmpfile function returns a null pointer.
    Forward references: the fopen function (7.21.5.3).

7.21.4.4 [The tmpnam function]


1           #include <stdio.h>
            char *tmpnam(char *s);
    Description
2   The tmpnam function generates a string that is a valid file name and that is not the same
    as the name of an existing file.270) The function is potentially capable of generating at

    least TMP_MAX different strings, but any or all of them may already be in use by existing
    files and thus not be suitable return values.
Footnote 270) Files created using strings generated by the tmpnam function are temporary only in the sense that
         their names should not collide with those generated by conventional naming rules for the
         implementation. It is still necessary to use the remove function to remove such files when their use
         is ended, and before program termination.
3   The tmpnam function generates a different string each time it is called.
4   Calls to the tmpnam function with a null pointer argument may introduce data races with
    each other. The implementation shall behave as if no library function calls the tmpnam
    function.
    Returns
5   If no suitable string can be generated, the tmpnam function returns a null pointer.
    Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
    internal static object and returns a pointer to that object (subsequent calls to the tmpnam
    function may modify the same object). If the argument is not a null pointer, it is assumed
    to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
    in that array and returns the argument as its value.
    Environmental limits
6   The value of the macro TMP_MAX shall be at least 25.

7.21.5 [File access functions]

 File access functions

7.21.5.1 [The fclose function]


1          #include <stdio.h>
           int fclose(FILE *stream);
    Description
2   A successful call to the fclose function causes the stream pointed to by stream to be
    flushed and the associated file to be closed. Any unwritten buffered data for the stream
    are delivered to the host environment to be written to the file; any unread buffered data
    are discarded. Whether or not the call succeeds, the stream is disassociated from the file
    and any buffer set by the setbuf or setvbuf function is disassociated from the stream
    (and deallocated if it was automatically allocated).
    Returns
3   The fclose function returns zero if the stream was successfully closed, or EOF if any
    errors were detected.

7.21.5.2 [The fflush function]


1           #include <stdio.h>
            int fflush(FILE *stream);
    Description
2   If stream points to an output stream or an update stream in which the most recent
    operation was not input, the fflush function causes any unwritten data for that stream
    to be delivered to the host environment to be written to the file; otherwise, the behavior is
    undefined.
3   If stream is a null pointer, the fflush function performs this flushing action on all
    streams for which the behavior is defined above.
    Returns
4   The fflush function sets the error indicator for the stream and returns EOF if a write
    error occurs, otherwise it returns zero.
    Forward references: the fopen function (7.21.5.3).

7.21.5.3 [The fopen function]


1           #include <stdio.h>
            FILE *fopen(const char * restrict filename,
                 const char * restrict mode);
    Description
2   The fopen function opens the file whose name is the string pointed to by filename,
    and associates a stream with it.
3   The argument mode points to a string. If the string is one of the following, the file is
    open in the indicated mode. Otherwise, the behavior is undefined.271)
    r                     open text file for reading
    w                     truncate to zero length or create text file for writing
    wx                    create text file for writing
    a                     append; open or create text file for writing at end-of-file
    rb                    open binary file for reading
    wb                    truncate to zero length or create binary file for writing

    wbx               create binary file for writing
    ab                append; open or create binary file for writing at end-of-file
    r+                open text file for update (reading and writing)
    w+                truncate to zero length or create text file for update
    w+x               create text file for update
    a+                append; open or create text file for update, writing at end-of-file
    r+b or rb+        open binary file for update (reading and writing)
    w+b or wb+        truncate to zero length or create binary file for update
    w+bx or wb+x      create binary file for update
    a+b or ab+        append; open or create binary file for update, writing at end-of-file
Footnote 271) If the string begins with one of the above sequences, the implementation might choose to ignore the
         remaining characters, or it might use them to select different kinds of a file (some of which might not
         conform to the properties in 7.21.2).
4   Opening a file with read mode ('r' as the first character in the mode argument) fails if
    the file does not exist or cannot be read.
5   Opening a file with exclusive mode ('x' as the last character in the mode argument)
    fails if the file already exists or cannot be created. Otherwise, the file is created with
    exclusive (also known as non-shared) access to the extent that the underlying system
    supports exclusive access.
6   Opening a file with append mode ('a' as the first character in the mode argument)
    causes all subsequent writes to the file to be forced to the then current end-of-file,
    regardless of intervening calls to the fseek function. In some implementations, opening
    a binary file with append mode ('b' as the second or third character in the above list of
    mode argument values) may initially position the file position indicator for the stream
    beyond the last data written, because of null character padding.
7   When a file is opened with update mode ('+' as the second or third character in the
    above list of mode argument values), both input and output may be performed on the
    associated stream. However, output shall not be directly followed by input without an
    intervening call to the fflush function or to a file positioning function (fseek,
    fsetpos, or rewind), and input shall not be directly followed by output without an
    intervening call to a file positioning function, unless the input operation encounters end-
    of-file. Opening (or creating) a text file with update mode may instead open (or create) a
    binary stream in some implementations.
8   When opened, a stream is fully buffered if and only if it can be determined not to refer to
    an interactive device. The error and end-of-file indicators for the stream are cleared.
    Returns
9   The fopen function returns a pointer to the object controlling the stream. If the open
    operation fails, fopen returns a null pointer.
    Forward references: file positioning functions (7.21.9).


7.21.5.4 [The freopen function]


1           #include <stdio.h>
            FILE *freopen(const char * restrict filename,
                 const char * restrict mode,
                 FILE * restrict stream);
    Description
2   The freopen function opens the file whose name is the string pointed to by filename
    and associates the stream pointed to by stream with it. The mode argument is used just
    as in the fopen function.272)
Footnote 272) The primary use of the freopen function is to change the file associated with a standard text stream
         (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
         returned by the fopen function may be assigned.
3   If filename is a null pointer, the freopen function attempts to change the mode of
    the stream to that specified by mode, as if the name of the file currently associated with
    the stream had been used. It is implementation-defined which changes of mode are
    permitted (if any), and under what circumstances.
4   The freopen function first attempts to close any file that is associated with the specified
    stream. Failure to close the file is ignored. The error and end-of-file indicators for the
    stream are cleared.
    Returns
5   The freopen function returns a null pointer if the open operation fails. Otherwise,
    freopen returns the value of stream.

7.21.5.5 [The setbuf function]


1           #include <stdio.h>
            void setbuf(FILE * restrict stream,
                 char * restrict buf);
    Description
2   Except that it returns no value, the setbuf function is equivalent to the setvbuf
    function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
    is a null pointer), with the value _IONBF for mode.

    Returns
3   The setbuf function returns no value.
    Forward references: the setvbuf function (7.21.5.6).

7.21.5.6 [The setvbuf function]


1           #include <stdio.h>
            int setvbuf(FILE * restrict stream,
                 char * restrict buf,
                 int mode, size_t size);
    Description
2   The setvbuf function may be used only after the stream pointed to by stream has
    been associated with an open file and before any other operation (other than an
    unsuccessful call to setvbuf) is performed on the stream. The argument mode
    determines how stream will be buffered, as follows: _IOFBF causes input/output to be
    fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
    input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
    used instead of a buffer allocated by the setvbuf function273) and the argument size
    specifies the size of the array; otherwise, size may determine the size of a buffer
    allocated by the setvbuf function. The contents of the array at any time are
    indeterminate.
    Returns
Footnote 273) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
         before a buffer that has automatic storage duration is deallocated upon block exit.
3   The setvbuf function returns zero on success, or nonzero if an invalid value is given
    for mode or if the request cannot be honored.


7.21.6 [Formatted input/output functions]


1   The formatted input/output functions shall behave as if there is a sequence point after the
    actions associated with each specifier.274)
Footnote 274) The fprintf functions perform writes to memory for the %n specifier.

7.21.6.1 [The fprintf function]


1            #include <stdio.h>
             int fprintf(FILE * restrict stream,
                  const char * restrict format, ...);
    Description
2   The fprintf function writes output to the stream pointed to by stream, under control
    of the string pointed to by format that specifies how subsequent arguments are
    converted for output. If there are insufficient arguments for the format, the behavior is
    undefined. If the format is exhausted while arguments remain, the excess arguments are
    evaluated (as always) but are otherwise ignored. The fprintf function returns when
    the end of the format string is encountered.
3   The format shall be a multibyte character sequence, beginning and ending in its initial
    shift state. The format is composed of zero or more directives: ordinary multibyte
    characters (not %), which are copied unchanged to the output stream; and conversion
    specifications, each of which results in fetching zero or more subsequent arguments,
    converting them, if applicable, according to the corresponding conversion specifier, and
    then writing the result to the output stream.
4   Each conversion specification is introduced by the character %. After the %, the following
    appear in sequence:
    -- Zero or more flags (in any order) that modify the meaning of the conversion
       specification.
    -- An optional minimum field width. If the converted value has fewer characters than the
       field width, it is padded with spaces (by default) on the left (or right, if the left
       adjustment flag, described later, has been given) to the field width. The field width
       takes the form of an asterisk * (described later) or a nonnegative decimal integer.275)
    -- An optional precision that gives the minimum number of digits to appear for the d, i,
       o, u, x, and X conversions, the number of digits to appear after the decimal-point
       character for a, A, e, E, f, and F conversions, the maximum number of significant
       digits for the g and G conversions, or the maximum number of bytes to be written for

        s conversions. The precision takes the form of a period (.) followed either by an
        asterisk * (described later) or by an optional decimal integer; if only the period is
        specified, the precision is taken as zero. If a precision appears with any other
        conversion specifier, the behavior is undefined.
    -- An optional length modifier that specifies the size of the argument.
    -- A conversion specifier character that specifies the type of conversion to be applied.
Footnote 275) Note that 0 is taken as a flag, not as the beginning of a field width.
5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
    this case, an int argument supplies the field width or precision. The arguments
    specifying field width, or precision, or both, shall appear (in that order) before the
    argument (if any) to be converted. A negative field width argument is taken as a - flag
    followed by a positive field width. A negative precision argument is taken as if the
    precision were omitted.
6   The flag characters and their meanings are:
    -        The result of the conversion is left-justified within the field. (It is right-justified if
             this flag is not specified.)
    +        The result of a signed conversion always begins with a plus or minus sign. (It
             begins with a sign only when a negative value is converted if this flag is not
             specified.)276)
    space If the first character of a signed conversion is not a sign, or if a signed conversion
          results in no characters, a space is prefixed to the result. If the space and + flags
          both appear, the space flag is ignored.
    #        The result is converted to an ``alternative form''. For o conversion, it increases
             the precision, if and only if necessary, to force the first digit of the result to be a
             zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
             conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
             and G conversions, the result of converting a floating-point number always
             contains a decimal-point character, even if no digits follow it. (Normally, a
             decimal-point character appears in the result of these conversions only if a digit
             follows it.) For g and G conversions, trailing zeros are not removed from the
             result. For other conversions, the behavior is undefined.
    0        For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
             (following any indication of sign or base) are used to pad to the field width rather
             than performing space padding, except when converting an infinity or NaN. If the
             0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X

              conversions, if a precision is specified, the 0 flag is ignored. For other
              conversions, the behavior is undefined.
Footnote 276) The results of all floating conversions of a negative zero, and of negative values that round to zero,
         include a minus sign.
7   The length modifiers and their meanings are:
    hh            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  signed char or unsigned char argument (the argument will have
                  been promoted according to the integer promotions, but its value shall be
                  converted to signed char or unsigned char before printing); or that
                  a following n conversion specifier applies to a pointer to a signed char
                  argument.
    h             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  short int or unsigned short int argument (the argument will
                  have been promoted according to the integer promotions, but its value shall
                  be converted to short int or unsigned short int before printing);
                  or that a following n conversion specifier applies to a pointer to a short
                  int argument.
    l (ell)       Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  long int or unsigned long int argument; that a following n
                  conversion specifier applies to a pointer to a long int argument; that a
                  following c conversion specifier applies to a wint_t argument; that a
                  following s conversion specifier applies to a pointer to a wchar_t
                  argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                  specifier.
    ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 long long int or unsigned long long int argument; or that a
                 following n conversion specifier applies to a pointer to a long long int
                 argument.
    j             Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                  an intmax_t or uintmax_t argument; or that a following n conversion
                  specifier applies to a pointer to an intmax_t argument.
    z             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  size_t or the corresponding signed integer type argument; or that a
                  following n conversion specifier applies to a pointer to a signed integer type
                  corresponding to size_t argument.
    t             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  ptrdiff_t or the corresponding unsigned integer type argument; or that a
                  following n conversion specifier applies to a pointer to a ptrdiff_t
                  argument.
    L              Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                   applies to a long double argument.
    If a length modifier appears with any conversion specifier other than as specified above,
    the behavior is undefined.
8   The conversion specifiers and their meanings are:
    d,i           The int argument is converted to signed decimal in the style [-]dddd. The
                  precision specifies the minimum number of digits to appear; if the value
                  being converted can be represented in fewer digits, it is expanded with
                  leading zeros. The default precision is 1. The result of converting a zero
                  value with a precision of zero is no characters.
    o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
            decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd ; the
            letters abcdef are used for x conversion and the letters ABCDEF for X
            conversion. The precision specifies the minimum number of digits to appear;
            if the value being converted can be represented in fewer digits, it is expanded
            with leading zeros. The default precision is 1. The result of converting a
            zero value with a precision of zero is no characters.
    f,F           A double argument representing a floating-point number is converted to
                  decimal notation in the style [-]ddd.ddd, where the number of digits after
                  the decimal-point character is equal to the precision specification. If the
                  precision is missing, it is taken as 6; if the precision is zero and the # flag is
                  not specified, no decimal-point character appears. If a decimal-point
                  character appears, at least one digit appears before it. The value is rounded to
                  the appropriate number of digits.
                  A double argument representing an infinity is converted in one of the styles
                  [-]inf or [-]infinity -- which style is implementation-defined. A
                  double argument representing a NaN is converted in one of the styles
                  [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
                  any n-char-sequence, is implementation-defined. The F conversion specifier
                  produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
                  respectively.277)
    e,E           A double argument representing a floating-point number is converted in the
                  style [-]d.ddd e±dd, where there is one digit (which is nonzero if the
                  argument is nonzero) before the decimal-point character and the number of
                  digits after it is equal to the precision; if the precision is missing, it is taken as

                  6; if the precision is zero and the # flag is not specified, no decimal-point
                  character appears. The value is rounded to the appropriate number of digits.
                  The E conversion specifier produces a number with E instead of e
                  introducing the exponent. The exponent always contains at least two digits,
                  and only as many more digits as necessary to represent the exponent. If the
                  value is zero, the exponent is zero.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    g,G           A double argument representing a floating-point number is converted in
                  style f or e (or in style F or E in the case of a G conversion specifier),
                  depending on the value converted and the precision. Let P equal the
                  precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
                  Then, if a conversion with style E would have an exponent of X :
                  -- if P > X  -4, the conversion is with style f (or F) and precision
                     P - ( X + 1).
                  -- otherwise, the conversion is with style e (or E) and precision P - 1.
                  Finally, unless the # flag is used, any trailing zeros are removed from the
                  fractional portion of the result and the decimal-point character is removed if
                  there is no fractional portion remaining.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    a,A           A double argument representing a floating-point number is converted in the
                  style [-]0xh.hhhh p±d, where there is one hexadecimal digit (which is
                  nonzero if the argument is a normalized floating-point number and is
                  otherwise unspecified) before the decimal-point character278) and the number
                  of hexadecimal digits after it is equal to the precision; if the precision is
                  missing and FLT_RADIX is a power of 2, then the precision is sufficient for
                  an exact representation of the value; if the precision is missing and
                  FLT_RADIX is not a power of 2, then the precision is sufficient to

                  distinguish279) values of type double, except that trailing zeros may be
                  omitted; if the precision is zero and the # flag is not specified, no decimal-
                  point character appears. The letters abcdef are used for a conversion and
                  the letters ABCDEF for A conversion. The A conversion specifier produces a
                  number with X and P instead of x and p. The exponent always contains at
                  least one digit, and only as many more digits as necessary to represent the
                  decimal exponent of 2. If the value is zero, the exponent is zero.
                  A double argument representing an infinity or NaN is converted in the style
                  of an f or F conversion specifier.
    c             If no l length modifier is present, the int argument is converted to an
                  unsigned char, and the resulting character is written.
                  If an l length modifier is present, the wint_t argument is converted as if by
                  an ls conversion specification with no precision and an argument that points
                  to the initial element of a two-element array of wchar_t, the first element
                  containing the wint_t argument to the lc conversion specification and the
                  second a null wide character.
    s             If no l length modifier is present, the argument shall be a pointer to the initial
                  element of an array of character type.280) Characters from the array are
                  written up to (but not including) the terminating null character. If the
                  precision is specified, no more than that many bytes are written. If the
                  precision is not specified or is greater than the size of the array, the array shall
                  contain a null character.
                  If an l length modifier is present, the argument shall be a pointer to the initial
                  element of an array of wchar_t type. Wide characters from the array are
                  converted to multibyte characters (each as if by a call to the wcrtomb
                  function, with the conversion state described by an mbstate_t object
                  initialized to zero before the first wide character is converted) up to and
                  including a terminating null wide character. The resulting multibyte
                  characters are written up to (but not including) the terminating null character
                  (byte). If no precision is specified, the array shall contain a null wide
                  character. If a precision is specified, no more than that many bytes are
                  written (including shift sequences, if any), and the array shall contain a null
                  wide character if, to equal the multibyte character sequence length given by

                    the precision, the function would need to access a wide character one past the
                    end of the array. In no case is a partial multibyte character written.281)
     p              The argument shall be a pointer to void. The value of the pointer is
                    converted to a sequence of printing characters, in an implementation-defined
                    manner.
     n              The argument shall be a pointer to signed integer into which is written the
                    number of characters written to the output stream so far by this call to
                    fprintf. No argument is converted, but one is consumed. If the conversion
                    specification includes any flags, a field width, or a precision, the behavior is
                    undefined.
     %              A % character is written. No argument is converted. The complete
                    conversion specification shall be %%.
Footnote 277) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
         the # and 0 flag characters have no effect.
Footnote 278) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
         that subsequent digits align to nibble (4-bit) boundaries.
Footnote 279) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
         FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
         might suffice depending on the implementation's scheme for determining the digit to the left of the
         decimal-point character.
Footnote 280) No special provisions are made for multibyte characters.
Footnote 281) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
9    If a conversion specification is invalid, the behavior is undefined.282) If any argument is
     not the correct type for the corresponding conversion specification, the behavior is
     undefined.
Footnote 282) See ``future library directions'' (7.31.11).
10   In no case does a nonexistent or small field width cause truncation of a field; if the result
     of a conversion is wider than the field width, the field is expanded to contain the
     conversion result.
11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
     to a hexadecimal floating number with the given precision.
     Recommended practice
12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
     representable in the given precision, the result should be one of the two adjacent numbers
     in hexadecimal floating style with the given precision, with the extra stipulation that the
     error should have a correct sign for the current rounding direction.
13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
     DECIMAL_DIG, then the result should be correctly rounded.283) If the number of
     significant decimal digits is more than DECIMAL_DIG but the source value is exactly
     representable with DECIMAL_DIG digits, then the result should be an exact
     representation with trailing zeros. Otherwise, the source value is bounded by two
     adjacent decimal strings L < U , both having DECIMAL_DIG significant digits; the value

     of the resultant decimal string D should satisfy L  D  U , with the extra stipulation that
     the error should have a correct sign for the current rounding direction.
     Returns
Footnote 283) For binary-to-decimal conversion, the result format's values are the numbers representable with the
          given format specifier. The number of significant digits is determined by the format specifier, and in
          the case of fixed-point conversion by the source value as well.
14   The fprintf function returns the number of characters transmitted, or a negative value
     if an output or encoding error occurred.
     Environmental limits
15   The number of characters that can be produced by any single conversion shall be at least
     4095.
16   EXAMPLE 1         To print a date and time in the form ``Sunday, July 3, 10:02'' followed by  to five decimal
     places:
              #include <math.h>
              #include <stdio.h>
              /* ... */
              char *weekday, *month;      // pointers to strings
              int day, hour, min;
              fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
                      weekday, month, day, hour, min);
              fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

17   EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
     members of the extended character set that consist of more than one byte each consist of exactly two bytes,
     the first of which is denoted here by a and the second by an uppercase letter.
18   Given the following wide string with length seven,
              static wchar_t wstr[] = L" X Yabc Z W";
     the seven calls
              fprintf(stdout,          "|1234567890123|\n");
              fprintf(stdout,          "|%13ls|\n", wstr);
              fprintf(stdout,          "|%-13.9ls|\n", wstr);
              fprintf(stdout,          "|%13.10ls|\n", wstr);
              fprintf(stdout,          "|%13.11ls|\n", wstr);
              fprintf(stdout,          "|%13.15ls|\n", &wstr[2]);
              fprintf(stdout,          "|%13lc|\n", (wint_t) wstr[5]);
     will print the following seven lines:
              |1234567890123|
              |   X Yabc Z W|
              | X Yabc Z    |
              |     X Yabc Z|
              |   X Yabc Z W|
              |      abc Z W|
              |            Z|

     Forward references: conversion state (7.29.6), the wcrtomb function (7.29.6.3.3).


7.21.6.2 [The fscanf function]


1           #include <stdio.h>
            int fscanf(FILE * restrict stream,
                 const char * restrict format, ...);
    Description
2   The fscanf function reads input from the stream pointed to by stream, under control
    of the string pointed to by format that specifies the admissible input sequences and how
    they are to be converted for assignment, using subsequent arguments as pointers to the
    objects to receive the converted input. If there are insufficient arguments for the format,
    the behavior is undefined. If the format is exhausted while arguments remain, the excess
    arguments are evaluated (as always) but are otherwise ignored.
3   The format shall be a multibyte character sequence, beginning and ending in its initial
    shift state. The format is composed of zero or more directives: one or more white-space
    characters, an ordinary multibyte character (neither % nor a white-space character), or a
    conversion specification. Each conversion specification is introduced by the character %.
    After the %, the following appear in sequence:
    -- An optional assignment-suppressing character *.
    -- An optional decimal integer greater than zero that specifies the maximum field width
       (in characters).
    -- An optional length modifier that specifies the size of the receiving object.
    -- A conversion specifier character that specifies the type of conversion to be applied.
4   The fscanf function executes each directive of the format in turn. When all directives
    have been executed, or if a directive fails (as detailed below), the function returns.
    Failures are described as input failures (due to the occurrence of an encoding error or the
    unavailability of input characters), or matching failures (due to inappropriate input).
5   A directive composed of white-space character(s) is executed by reading input up to the
    first non-white-space character (which remains unread), or until no more characters can
    be read. The directive never fails.
6   A directive that is an ordinary multibyte character is executed by reading the next
    characters of the stream. If any of those characters differ from the ones composing the
    directive, the directive fails and the differing and subsequent characters remain unread.
    Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
    read, the directive fails.
7   A directive that is a conversion specification defines a set of matching input sequences, as
    described below for each specifier. A conversion specification is executed in the

     following steps:
8    Input white-space characters (as specified by the isspace function) are skipped, unless
     the specification includes a [, c, or n specifier.284)
Footnote 284) These white-space characters are not counted against a specified field width.
9    An input item is read from the stream, unless the specification includes an n specifier. An
     input item is defined as the longest sequence of input characters which does not exceed
     any specified field width and which is, or is a prefix of, a matching input sequence.285)
     The first character, if any, after the input item remains unread. If the length of the input
     item is zero, the execution of the directive fails; this condition is a matching failure unless
     end-of-file, an encoding error, or a read error prevented input from the stream, in which
     case it is an input failure.
Footnote 285) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
          that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.
10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
     count of input characters) is converted to a type appropriate to the conversion specifier. If
     the input item is not a matching sequence, the execution of the directive fails: this
     condition is a matching failure. Unless assignment suppression was indicated by a *, the
     result of the conversion is placed in the object pointed to by the first argument following
     the format argument that has not already received a conversion result. If this object
     does not have an appropriate type, or if the result of the conversion cannot be represented
     in the object, the behavior is undefined.
11   The length modifiers and their meanings are:
     hh             Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to signed char or unsigned char.
     h              Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to short int or unsigned short
                    int.
     l (ell)        Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to long int or unsigned long
                    int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                    an argument with type pointer to double; or that a following c, s, or [
                    conversion specifier applies to an argument with type pointer to wchar_t.
     ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long long int or unsigned
                  long long int.

     j            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to intmax_t or uintmax_t.
     z            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to size_t or the corresponding signed
                  integer type.
     t            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to ptrdiff_t or the corresponding
                  unsigned integer type.
     L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                  applies to an argument with type pointer to long double.
     If a length modifier appears with any conversion specifier other than as specified above,
     the behavior is undefined.
12   The conversion specifiers and their meanings are:
     d           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the strtol function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 signed integer.
     i           Matches an optionally signed integer, whose format is the same as expected
                 for the subject sequence of the strtol function with the value 0 for the
                 base argument. The corresponding argument shall be a pointer to signed
                 integer.
     o           Matches an optionally signed octal integer, whose format is the same as
                 expected for the subject sequence of the strtoul function with the value 8
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     u           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the strtoul function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     x           Matches an optionally signed hexadecimal integer, whose format is the same
                 as expected for the subject sequence of the strtoul function with the value
                 16 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
             format is the same as expected for the subject sequence of the strtod
             function. The corresponding argument shall be a pointer to floating.
    c             Matches a sequence of characters of exactly the number specified by the field
                  width (1 if no field width is present in the directive).286)
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence. No null character is added.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character in the
                  sequence is converted to a wide character as if by a call to the mbrtowc
                  function, with the conversion state described by an mbstate_t object
                  initialized to zero before the first multibyte character is converted. The
                  corresponding argument shall be a pointer to the initial element of an array of
                  wchar_t large enough to accept the resulting sequence of wide characters.
                  No null wide character is added.
    s             Matches a sequence of non-white-space characters.286)
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence and a terminating null character, which will be added automatically.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character is
                  converted to a wide character as if by a call to the mbrtowc function, with
                  the conversion state described by an mbstate_t object initialized to zero
                  before the first multibyte character is converted. The corresponding argument
                  shall be a pointer to the initial element of an array of wchar_t large enough
                  to accept the sequence and the terminating null wide character, which will be
                  added automatically.
    [             Matches a nonempty sequence of characters from a set of expected characters
                  (the scanset ).286)
                  If no l length modifier is present, the corresponding argument shall be a
                  pointer to the initial element of a character array large enough to accept the
                  sequence and a terminating null character, which will be added automatically.
                  If an l length modifier is present, the input shall be a sequence of multibyte
                  characters that begins in the initial shift state. Each multibyte character is
                  converted to a wide character as if by a call to the mbrtowc function, with
                  the conversion state described by an mbstate_t object initialized to zero

                    before the first multibyte character is converted. The corresponding argument
                    shall be a pointer to the initial element of an array of wchar_t large enough
                    to accept the sequence and the terminating null wide character, which will be
                    added automatically.
                    The conversion specifier includes all subsequent characters in the format
                    string, up to and including the matching right bracket (]). The characters
                    between the brackets (the scanlist ) compose the scanset, unless the character
                    after the left bracket is a circumflex (^), in which case the scanset contains all
                    characters that do not appear in the scanlist between the circumflex and the
                    right bracket. If the conversion specifier begins with [] or [^], the right
                    bracket character is in the scanlist and the next following right bracket
                    character is the matching right bracket that ends the specification; otherwise
                    the first following right bracket character is the one that ends the
                    specification. If a - character is in the scanlist and is not the first, nor the
                    second where the first character is a ^, nor the last character, the behavior is
                    implementation-defined.
     p              Matches an implementation-defined set of sequences, which should be the
                    same as the set of sequences that may be produced by the %p conversion of
                    the fprintf function. The corresponding argument shall be a pointer to a
                    pointer to void. The input item is converted to a pointer value in an
                    implementation-defined manner. If the input item is a value converted earlier
                    during the same program execution, the pointer that results shall compare
                    equal to that value; otherwise the behavior of the %p conversion is undefined.
     n              No input is consumed. The corresponding argument shall be a pointer to
                    signed integer into which is to be written the number of characters read from
                    the input stream so far by this call to the fscanf function. Execution of a
                    %n directive does not increment the assignment count returned at the
                    completion of execution of the fscanf function. No argument is converted,
                    but one is consumed. If the conversion specification includes an assignment-
                    suppressing character or a field width, the behavior is undefined.
     %              Matches a single % character; no conversion or assignment occurs. The
                    complete conversion specification shall be %%.
Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
Footnote 286) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
         conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
         resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.
13   If a conversion specification is invalid, the behavior is undefined.287)
Footnote 287) See ``future library directions'' (7.31.11).
14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
     respectively, a, e, f, g, and x.

15   Trailing white space (including new-line characters) is left unread unless matched by a
     directive. The success of literal matches and suppressed assignments is not directly
     determinable other than via the %n directive.
     Returns
16   The fscanf function returns the value of the macro EOF if an input failure occurs
     before the first conversion (if any) has completed. Otherwise, the function returns the
     number of input items assigned, which can be fewer than provided for, or even zero, in
     the event of an early matching failure.
17   EXAMPLE 1        The call:
              #include <stdio.h>
              /* ... */
              int n, i; float x; char name[50];
              n = fscanf(stdin, "%d%f%s", &i, &x, name);
     with the input line:
              25 54.32E-1 thompson
     will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
     thompson\0.

18   EXAMPLE 2        The call:
              #include <stdio.h>
              /* ... */
              int i; float x; char name[50];
              fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
     with input:
              56789 0123 56a72
     will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
     sequence 56\0. The next character read from the input stream will be a.

19   EXAMPLE 3        To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
              #include <stdio.h>
              /* ... */
              int count; float quant; char units[21], item[21];
              do {
                      count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
                      fscanf(stdin,"%*[^\n]");
              } while (!feof(stdin) && !ferror(stdin));
20   If the stdin stream contains the following lines:
              2 quarts of oil
              -12.8degrees Celsius
              lots of luck
              10.0LBS     of
              dirt
              100ergs of energy

     the execution of the above example will be analogous to the following assignments:
               quant     =   2; strcpy(units, "quarts"); strcpy(item, "oil");
               count     =   3;
               quant     =   -12.8; strcpy(units, "degrees");
               count     =   2; // "C" fails to match "o"
               count     =   0; // "l" fails to match "%f"
               quant     =   10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
               count     =   3;
               count     =   0; // "100e" fails to match "%f"
               count     =   EOF;

21   EXAMPLE 4         In:
               #include <stdio.h>
               /* ... */
               int d1, d2, n1, n2, i;
               i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
     the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure, the value
     of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.

22   EXAMPLE 5         The call:
               #include <stdio.h>
               /* ... */
               int n, i;
               n = sscanf("foo %           bar     42", "foo%%bar%d", &i);
     will assign to n the value 1 and to i the value 42 because input white-space characters are skipped for both
     the % and d conversion specifiers.

23   EXAMPLE 6 In these examples, multibyte characters do have a state-dependent encoding, and the
     members of the extended character set that consist of more than one byte each consist of exactly two bytes,
     the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
     such when in the alternate shift state. The shift sequences are denoted by  and , in which the first causes
     entry into the alternate shift state.
24   After the call:
               #include <stdio.h>
               /* ... */
               char str[50];
               fscanf(stdin, "a%s", str);
     with the input line:
               a X Y bc
     str will contain  X Y\0 assuming that none of the bytes of the shift sequences (or of the multibyte
     characters, in the more general case) appears to be a single-byte white-space character.
25   In contrast, after the call:
             #include <stdio.h>
             #include <stddef.h>
             /* ... */
             wchar_t wstr[50];
             fscanf(stdin, "a%ls", wstr);
     with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
     terminating null wide character.
26   However, the call:
             #include <stdio.h>
             #include <stddef.h>
             /* ... */
             wchar_t wstr[50];
             fscanf(stdin, "a X%ls", wstr);
     with the same input line will return zero due to a matching failure against the  sequence in the format
     string.
27   Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
     character Y, after the call:
             #include <stdio.h>
             #include <stddef.h>
             /* ... */
             wchar_t wstr[50];
             fscanf(stdin, "a Y%ls", wstr);
     with the same input line, zero will again be returned, but stdin will be left with a partially consumed
     multibyte character.

     Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
     strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
     (7.29.6), the wcrtomb function (7.29.6.3.3).

7.21.6.3 [The printf function]


1            #include <stdio.h>
             int printf(const char * restrict format, ...);
     Description
2    The printf function is equivalent to fprintf with the argument stdout interposed
     before the arguments to printf.
     Returns
3    The printf function returns the number of characters transmitted, or a negative value if
     an output or encoding error occurred.

7.21.6.4 [The scanf function]


1           #include <stdio.h>
            int scanf(const char * restrict format, ...);
    Description
2   The scanf function is equivalent to fscanf with the argument stdin interposed
    before the arguments to scanf.
    Returns
3   The scanf function returns the value of the macro EOF if an input failure occurs before
    the first conversion (if any) has completed. Otherwise, the scanf function returns the
    number of input items assigned, which can be fewer than provided for, or even zero, in
    the event of an early matching failure.

7.21.6.5 [The snprintf function]


1           #include <stdio.h>
            int snprintf(char * restrict s, size_t n,
                 const char * restrict format, ...);
    Description
2   The snprintf function is equivalent to fprintf, except that the output is written into
    an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
    and s may be a null pointer. Otherwise, output characters beyond the n-1st are
    discarded rather than being written to the array, and a null character is written at the end
    of the characters actually written into the array. If copying takes place between objects
    that overlap, the behavior is undefined.
    Returns
3   The snprintf function returns the number of characters that would have been written
    had n been sufficiently large, not counting the terminating null character, or a negative
    value if an encoding error occurred. Thus, the null-terminated output has been
    completely written if and only if the returned value is nonnegative and less than n.

7.21.6.6 [The sprintf function]


1           #include <stdio.h>
            int sprintf(char * restrict s,
                 const char * restrict format, ...);
    Description
2   The sprintf function is equivalent to fprintf, except that the output is written into
    an array (specified by the argument s) rather than to a stream. A null character is written
    at the end of the characters written; it is not counted as part of the returned value. If
    copying takes place between objects that overlap, the behavior is undefined.
    Returns
3   The sprintf function returns the number of characters written in the array, not
    counting the terminating null character, or a negative value if an encoding error occurred.

7.21.6.7 [The sscanf function]


1          #include <stdio.h>
           int sscanf(const char * restrict s,
                const char * restrict format, ...);
    Description
2   The sscanf function is equivalent to fscanf, except that input is obtained from a
    string (specified by the argument s) rather than from a stream. Reaching the end of the
    string is equivalent to encountering end-of-file for the fscanf function. If copying
    takes place between objects that overlap, the behavior is undefined.
    Returns
3   The sscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the sscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.21.6.8 [The vfprintf function]


1          #include <stdarg.h>
           #include <stdio.h>
           int vfprintf(FILE * restrict stream,
                const char * restrict format,
                va_list arg);
    Description
2   The vfprintf function is equivalent to fprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfprintf function does not invoke the

    va_end macro.288)
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vfprintf function returns the number of characters transmitted, or a negative
    value if an output or encoding error occurred.
4   EXAMPLE       The following shows the use of the vfprintf function in a general error-reporting routine.
            #include <stdarg.h>
            #include <stdio.h>
            void error(char *function_name, char *format, ...)
            {
                  va_list args;
                    va_start(args, format);
                    // print out name of function causing error
                    fprintf(stderr, "ERROR in %s: ", function_name);
                    // print out remainder of message
                    vfprintf(stderr, format, args);
                    va_end(args);
            }


7.21.6.9 [The vfscanf function]


1           #include <stdarg.h>
            #include <stdio.h>
            int vfscanf(FILE * restrict stream,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vfscanf function is equivalent to fscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfscanf function does not invoke the
    va_end macro.288)
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vfscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vfscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.


7.21.6.10 [The vprintf function]


1          #include <stdarg.h>
           #include <stdio.h>
           int vprintf(const char * restrict format,
                va_list arg);
    Description
2   The vprintf function is equivalent to printf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vprintf function does not invoke the
    va_end macro.288)
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vprintf function returns the number of characters transmitted, or a negative value
    if an output or encoding error occurred.

7.21.6.11 [The vscanf function]


1          #include <stdarg.h>
           #include <stdio.h>
           int vscanf(const char * restrict format,
                va_list arg);
    Description
2   The vscanf function is equivalent to scanf, with the variable argument list replaced
    by arg, which shall have been initialized by the va_start macro (and possibly
    subsequent va_arg calls). The vscanf function does not invoke the va_end
    macro.288)
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.21.6.12 [The vsnprintf function]


1           #include <stdarg.h>
            #include <stdio.h>
            int vsnprintf(char * restrict s, size_t n,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vsnprintf function is equivalent to snprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsnprintf function does not invoke the
    va_end macro.288) If copying takes place between objects that overlap, the behavior is
    undefined.
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vsnprintf function returns the number of characters that would have been written
    had n been sufficiently large, not counting the terminating null character, or a negative
    value if an encoding error occurred. Thus, the null-terminated output has been
    completely written if and only if the returned value is nonnegative and less than n.

7.21.6.13 [The vsprintf function]


1           #include <stdarg.h>
            #include <stdio.h>
            int vsprintf(char * restrict s,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vsprintf function is equivalent to sprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsprintf function does not invoke the
    va_end macro.288) If copying takes place between objects that overlap, the behavior is
    undefined.
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vsprintf function returns the number of characters written in the array, not
    counting the terminating null character, or a negative value if an encoding error occurred.

7.21.6.14 [The vsscanf function]


1           #include <stdarg.h>
            #include <stdio.h>
            int vsscanf(const char * restrict s,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vsscanf function is equivalent to sscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsscanf function does not invoke the
    va_end macro.288)
    Returns
Footnote 288) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vsscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vsscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.21.7 [Character input/output functions]

 Character input/output functions

7.21.7.1 [The fgetc function]


1           #include <stdio.h>
            int fgetc(FILE *stream);
    Description
2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
    next character is present, the fgetc function obtains that character as an unsigned
    char converted to an int and advances the associated file position indicator for the
    stream (if defined).
    Returns
3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
    of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
    fgetc function returns the next character from the input stream pointed to by stream.
    If a read error occurs, the error indicator for the stream is set and the fgetc function
    returns EOF.289)

Footnote 289) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.

7.21.7.2 [The fgets function]


1           #include <stdio.h>
            char *fgets(char * restrict s, int n,
                 FILE * restrict stream);
    Description
2   The fgets function reads at most one less than the number of characters specified by n
    from the stream pointed to by stream into the array pointed to by s. No additional
    characters are read after a new-line character (which is retained) or after end-of-file. A
    null character is written immediately after the last character read into the array.
    Returns
3   The fgets function returns s if successful. If end-of-file is encountered and no
    characters have been read into the array, the contents of the array remain unchanged and a
    null pointer is returned. If a read error occurs during the operation, the array contents are
    indeterminate and a null pointer is returned.

7.21.7.3 [The fputc function]


1           #include <stdio.h>
            int fputc(int c, FILE *stream);
    Description
2   The fputc function writes the character specified by c (converted to an unsigned
    char) to the output stream pointed to by stream, at the position indicated by the
    associated file position indicator for the stream (if defined), and advances the indicator
    appropriately. If the file cannot support positioning requests, or if the stream was opened
    with append mode, the character is appended to the output stream.
    Returns
3   The fputc function returns the character written. If a write error occurs, the error
    indicator for the stream is set and fputc returns EOF.

7.21.7.4 [The fputs function]


1           #include <stdio.h>
            int fputs(const char * restrict s,
                 FILE * restrict stream);

    Description
2   The fputs function writes the string pointed to by s to the stream pointed to by
    stream. The terminating null character is not written.
    Returns
3   The fputs function returns EOF if a write error occurs; otherwise it returns a
    nonnegative value.

7.21.7.5 [The getc function]


1          #include <stdio.h>
           int getc(FILE *stream);
    Description
2   The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
    may evaluate stream more than once, so the argument should never be an expression
    with side effects.
    Returns
3   The getc function returns the next character from the input stream pointed to by
    stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
    getc returns EOF. If a read error occurs, the error indicator for the stream is set and
    getc returns EOF.

7.21.7.6 [The getchar function]


1          #include <stdio.h>
           int getchar(void);
    Description
2   The getchar function is equivalent to getc with the argument stdin.
    Returns
3   The getchar function returns the next character from the input stream pointed to by
    stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
    getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
    getchar returns EOF.

7.21.7.7 [The putc function]


1           #include <stdio.h>
            int putc(int c, FILE *stream);
    Description
2   The putc function is equivalent to fputc, except that if it is implemented as a macro, it
    may evaluate stream more than once, so that argument should never be an expression
    with side effects.
    Returns
3   The putc function returns the character written. If a write error occurs, the error
    indicator for the stream is set and putc returns EOF.

7.21.7.8 [The putchar function]


1           #include <stdio.h>
            int putchar(int c);
    Description
2   The putchar function is equivalent to putc with the second argument stdout.
    Returns
3   The putchar function returns the character written. If a write error occurs, the error
    indicator for the stream is set and putchar returns EOF.

7.21.7.9 [The puts function]


1           #include <stdio.h>
            int puts(const char *s);
    Description
2   The puts function writes the string pointed to by s to the stream pointed to by stdout,
    and appends a new-line character to the output. The terminating null character is not
    written.
    Returns
3   The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
    value.

7.21.7.10 [The ungetc function]


1            #include <stdio.h>
             int ungetc(int c, FILE *stream);
    Description
2   The ungetc function pushes the character specified by c (converted to an unsigned
    char) back onto the input stream pointed to by stream. Pushed-back characters will be
    returned by subsequent reads on that stream in the reverse order of their pushing. A
    successful intervening call (with the stream pointed to by stream) to a file positioning
    function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
    stream. The external storage corresponding to the stream is unchanged.
3   One character of pushback is guaranteed. If the ungetc function is called too many
    times on the same stream without an intervening read or file positioning operation on that
    stream, the operation may fail.
4   If the value of c equals that of the macro EOF, the operation fails and the input stream is
    unchanged.
5   A successful call to the ungetc function clears the end-of-file indicator for the stream.
    The value of the file position indicator for the stream after reading or discarding all
    pushed-back characters shall be the same as it was before the characters were pushed
    back. For a text stream, the value of its file position indicator after a successful call to the
    ungetc function is unspecified until all pushed-back characters are read or discarded.
    For a binary stream, its file position indicator is decremented by each successful call to
    the ungetc function; if its value was zero before a call, it is indeterminate after the
    call.290)
    Returns
Footnote 290) See ``future library directions'' (7.31.11).
6   The ungetc function returns the character pushed back after conversion, or EOF if the
    operation fails.
    Forward references: file positioning functions (7.21.9).


7.21.8 [Direct input/output functions]

 Direct input/output functions

7.21.8.1 [The fread function]


1           #include <stdio.h>
            size_t fread(void * restrict ptr,
                 size_t size, size_t nmemb,
                 FILE * restrict stream);
    Description
2   The fread function reads, into the array pointed to by ptr, up to nmemb elements
    whose size is specified by size, from the stream pointed to by stream. For each
    object, size calls are made to the fgetc function and the results stored, in the order
    read, in an array of unsigned char exactly overlaying the object. The file position
    indicator for the stream (if defined) is advanced by the number of characters successfully
    read. If an error occurs, the resulting value of the file position indicator for the stream is
    indeterminate. If a partial element is read, its value is indeterminate.
    Returns
3   The fread function returns the number of elements successfully read, which may be
    less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
    fread returns zero and the contents of the array and the state of the stream remain
    unchanged.

7.21.8.2 [The fwrite function]


1           #include <stdio.h>
            size_t fwrite(const void * restrict ptr,
                 size_t size, size_t nmemb,
                 FILE * restrict stream);
    Description
2   The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
    whose size is specified by size, to the stream pointed to by stream. For each object,
    size calls are made to the fputc function, taking the values (in order) from an array of
    unsigned char exactly overlaying the object. The file position indicator for the
    stream (if defined) is advanced by the number of characters successfully written. If an
    error occurs, the resulting value of the file position indicator for the stream is
    indeterminate.
    Returns
3   The fwrite function returns the number of elements successfully written, which will be
    less than nmemb only if a write error is encountered. If size or nmemb is zero,
    fwrite returns zero and the state of the stream remains unchanged.

7.21.9 [File positioning functions]

 File positioning functions

7.21.9.1 [The fgetpos function]


1          #include <stdio.h>
           int fgetpos(FILE * restrict stream,
                fpos_t * restrict pos);
    Description
2   The fgetpos function stores the current values of the parse state (if any) and file
    position indicator for the stream pointed to by stream in the object pointed to by pos.
    The values stored contain unspecified information usable by the fsetpos function for
    repositioning the stream to its position at the time of the call to the fgetpos function.
    Returns
3   If successful, the fgetpos function returns zero; on failure, the fgetpos function
    returns nonzero and stores an implementation-defined positive value in errno.
    Forward references: the fsetpos function (7.21.9.3).

7.21.9.2 [The fseek function]


1          #include <stdio.h>
           int fseek(FILE *stream, long int offset, int whence);
    Description
2   The fseek function sets the file position indicator for the stream pointed to by stream.
    If a read or write error occurs, the error indicator for the stream is set and fseek fails.
3   For a binary stream, the new position, measured in characters from the beginning of the
    file, is obtained by adding offset to the position specified by whence. The specified
    position is the beginning of the file if whence is SEEK_SET, the current value of the file
    position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
    meaningfully support fseek calls with a whence value of SEEK_END.
4   For a text stream, either offset shall be zero, or offset shall be a value returned by
    an earlier successful call to the ftell function on a stream associated with the same file
    and whence shall be SEEK_SET.

5   After determining the new position, a successful call to the fseek function undoes any
    effects of the ungetc function on the stream, clears the end-of-file indicator for the
    stream, and then establishes the new position. After a successful fseek call, the next
    operation on an update stream may be either input or output.
    Returns
6   The fseek function returns nonzero only for a request that cannot be satisfied.
    Forward references: the ftell function (7.21.9.4).

7.21.9.3 [The fsetpos function]


1           #include <stdio.h>
            int fsetpos(FILE *stream, const fpos_t *pos);
    Description
2   The fsetpos function sets the mbstate_t object (if any) and file position indicator
    for the stream pointed to by stream according to the value of the object pointed to by
    pos, which shall be a value obtained from an earlier successful call to the fgetpos
    function on a stream associated with the same file. If a read or write error occurs, the
    error indicator for the stream is set and fsetpos fails.
3   A successful call to the fsetpos function undoes any effects of the ungetc function
    on the stream, clears the end-of-file indicator for the stream, and then establishes the new
    parse state and position. After a successful fsetpos call, the next operation on an
    update stream may be either input or output.
    Returns
4   If successful, the fsetpos function returns zero; on failure, the fsetpos function
    returns nonzero and stores an implementation-defined positive value in errno.

7.21.9.4 [The ftell function]


1           #include <stdio.h>
            long int ftell(FILE *stream);
    Description
2   The ftell function obtains the current value of the file position indicator for the stream
    pointed to by stream. For a binary stream, the value is the number of characters from
    the beginning of the file. For a text stream, its file position indicator contains unspecified
    information, usable by the fseek function for returning the file position indicator for the
    stream to its position at the time of the ftell call; the difference between two such
    return values is not necessarily a meaningful measure of the number of characters written

    or read.
    Returns
3   If successful, the ftell function returns the current value of the file position indicator
    for the stream. On failure, the ftell function returns -1L and stores an
    implementation-defined positive value in errno.

7.21.9.5 [The rewind function]


1          #include <stdio.h>
           void rewind(FILE *stream);
    Description
2   The rewind function sets the file position indicator for the stream pointed to by
    stream to the beginning of the file. It is equivalent to
           (void)fseek(stream, 0L, SEEK_SET)
    except that the error indicator for the stream is also cleared.
    Returns
3   The rewind function returns no value.

7.21.10 [Error-handling functions]

 Error-handling functions

7.21.10.1 [The clearerr function]


1          #include <stdio.h>
           void clearerr(FILE *stream);
    Description
2   The clearerr function clears the end-of-file and error indicators for the stream pointed
    to by stream.
    Returns
3   The clearerr function returns no value.

7.21.10.2 [The feof function]


1           #include <stdio.h>
            int feof(FILE *stream);
    Description
2   The feof function tests the end-of-file indicator for the stream pointed to by stream.
    Returns
3   The feof function returns nonzero if and only if the end-of-file indicator is set for
    stream.

7.21.10.3 [The ferror function]


1           #include <stdio.h>
            int ferror(FILE *stream);
    Description
2   The ferror function tests the error indicator for the stream pointed to by stream.
    Returns
3   The ferror function returns nonzero if and only if the error indicator is set for
    stream.

7.21.10.4 [The perror function]


1           #include <stdio.h>
            void perror(const char *s);
    Description
2   The perror function maps the error number in the integer expression errno to an
    error message. It writes a sequence of characters to the standard error stream thus: first
    (if s is not a null pointer and the character pointed to by s is not the null character), the
    string pointed to by s followed by a colon (:) and a space; then an appropriate error
    message string followed by a new-line character. The contents of the error message
    strings are the same as those returned by the strerror function with argument errno.
    Returns
3   The perror function returns no value.
    Forward references: the strerror function (7.24.6.2).

7.22 [General utilities ]


1   The header <stdlib.h> declares five types and several functions of general utility, and
    defines several macros.291)
Footnote 291) See ``future library directions'' (7.31.12).
2   The types declared are size_t and wchar_t (both described in 7.19),
             div_t
    which is a structure type that is the type of the value returned by the div function,
             ldiv_t
    which is a structure type that is the type of the value returned by the ldiv function, and
             lldiv_t
    which is a structure type that is the type of the value returned by the lldiv function.
3   The macros defined are NULL (described in 7.19);
             EXIT_FAILURE
    and
             EXIT_SUCCESS
    which expand to integer constant expressions that can be used as the argument to the
    exit function to return unsuccessful or successful termination status, respectively, to the
    host environment;
             RAND_MAX
    which expands to an integer constant expression that is the maximum value returned by
    the rand function; and
             MB_CUR_MAX
    which expands to a positive integer expression with type size_t that is the maximum
    number of bytes in a multibyte character for the extended character set specified by the
    current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.


7.22.1 [Numeric conversion functions]


1   The functions atof, atoi, atol, and atoll need not affect the value of the integer
    expression errno on an error. If the value of the result cannot be represented, the
    behavior is undefined.

7.22.1.1 [The atof function]


1           #include <stdlib.h>
            double atof(const char *nptr);
    Description
2   The atof function converts the initial portion of the string pointed to by nptr to
    double representation. Except for the behavior on error, it is equivalent to
            strtod(nptr, (char **)NULL)
    Returns
3   The atof function returns the converted value.
    Forward references: the strtod, strtof, and strtold functions (7.22.1.3).

7.22.1.2 [The atoi, atol, and atoll functions]


1           #include <stdlib.h>
            int atoi(const char *nptr);
            long int atol(const char *nptr);
            long long int atoll(const char *nptr);
    Description
2   The atoi, atol, and atoll functions convert the initial portion of the string pointed
    to by nptr to int, long int, and long long int representation, respectively.
    Except for the behavior on error, they are equivalent to
            atoi: (int)strtol(nptr, (char **)NULL, 10)
            atol: strtol(nptr, (char **)NULL, 10)
            atoll: strtoll(nptr, (char **)NULL, 10)
    Returns
3   The atoi, atol, and atoll functions return the converted value.
    Forward references: the strtol, strtoll, strtoul, and strtoull functions
    (7.22.1.4).


7.22.1.3 [The strtod, strtof, and strtold functions]


1          #include <stdlib.h>
           double strtod(const char * restrict nptr,
                char ** restrict endptr);
           float strtof(const char * restrict nptr,
                char ** restrict endptr);
           long double strtold(const char * restrict nptr,
                char ** restrict endptr);
    Description
2   The strtod, strtof, and strtold functions convert the initial portion of the string
    pointed to by nptr to double, float, and long double representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space characters (as specified by the isspace function), a
    subject sequence resembling a floating-point constant or representing an infinity or NaN;
    and a final string of one or more unrecognized characters, including the terminating null
    character of the input string. Then, they attempt to convert the subject sequence to a
    floating-point number, and return the result.
3   The expected form of the subject sequence is an optional plus or minus sign, then one of
    the following:
    -- a nonempty sequence of decimal digits optionally containing a decimal-point
       character, then an optional exponent part as defined in 6.4.4.2;
    -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
       decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
    -- INF or INFINITY, ignoring case
    -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
               n-char-sequence:
                      digit
                      nondigit
                      n-char-sequence digit
                      n-char-sequence nondigit
    The subject sequence is defined as the longest initial subsequence of the input string,
    starting with the first non-white-space character, that is of the expected form. The subject
    sequence contains no characters if the input string is not of the expected form.
4   If the subject sequence has the expected form for a floating-point number, the sequence of
    characters starting with the first digit or the decimal-point character (whichever occurs
    first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
    decimal-point character is used in place of a period, and that if neither an exponent part
    nor a decimal-point character appears in a decimal floating point number, or if a binary
    exponent part does not appear in a hexadecimal floating point number, an exponent part
    of the appropriate type with value zero is assumed to follow the last digit in the string. If
    the subject sequence begins with a minus sign, the sequence is interpreted as negated.292)
    A character sequence INF or INFINITY is interpreted as an infinity, if representable in
    the return type, else like a floating constant that is too large for the range of the return
    type. A character sequence NAN or NAN(n-char-sequenceopt) is interpreted as a quiet
    NaN, if supported in the return type, else like a subject sequence part that does not have
    the expected form; the meaning of the n-char sequence is implementation-defined.293) A
    pointer to the final string is stored in the object pointed to by endptr, provided that
    endptr is not a null pointer.
Footnote 292) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
         negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
         methods may yield different results if rounding is toward positive or negative infinity. In either case,
         the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
Footnote 293) An implementation may use the n-char sequence to determine extra information to be represented in
         the NaN's significand.
5   If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
    value resulting from the conversion is correctly rounded.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Recommended practice
8   If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
    the result is not exactly representable, the result should be one of the two numbers in the
    appropriate internal format that are adjacent to the hexadecimal floating source value,
    with the extra stipulation that the error should have a correct sign for the current rounding
    direction.
9   If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
    <float.h>) significant digits, the result should be correctly rounded. If the subject
    sequence D has the decimal form and more than DECIMAL_DIG significant digits,
    consider the two bounding, adjacent decimal strings L and U , both having
    DECIMAL_DIG significant digits, such that the values of L , D, and U satisfy L  D  U .
    The result should be one of the (equal or adjacent) values that would be obtained by
    correctly rounding L and U according to the current rounding direction, with the extra

     stipulation that the error with respect to D should have a correct sign for the current
     rounding direction.294)
     Returns
Footnote 294) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
          to the same internal floating value, but if not will round to adjacent values.
10   The functions return the converted value, if any. If no conversion could be performed,
     zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
     plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
     return type and sign of the value), and the value of the macro ERANGE is stored in
     errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
     no greater than the smallest normalized positive number in the return type; whether
     errno acquires the value ERANGE is implementation-defined.

7.22.1.4 [The strtol, strtoll, strtoul, and strtoull functions]


1            #include <stdlib.h>
             long int strtol(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             long long int strtoll(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             unsigned long int strtoul(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             unsigned long long int strtoull(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
     Description
2    The strtol, strtoll, strtoul, and strtoull functions convert the initial
     portion of the string pointed to by nptr to long int, long long int, unsigned
     long int, and unsigned long long int representation, respectively. First,
     they decompose the input string into three parts: an initial, possibly empty, sequence of
     white-space characters (as specified by the isspace function), a subject sequence

    resembling an integer represented in some radix determined by the value of base, and a
    final string of one or more unrecognized characters, including the terminating null
    character of the input string. Then, they attempt to convert the subject sequence to an
    integer, and return the result.
3   If the value of base is zero, the expected form of the subject sequence is that of an
    integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
    not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
    expected form of the subject sequence is a sequence of letters and digits representing an
    integer with the radix specified by base, optionally preceded by a plus or minus sign,
    but not including an integer suffix. The letters from a (or A) through z (or Z) are
    ascribed the values 10 through 35; only letters and digits whose ascribed values are less
    than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
    optionally precede the sequence of letters and digits, following the sign if present.
4   The subject sequence is defined as the longest initial subsequence of the input string,
    starting with the first non-white-space character, that is of the expected form. The subject
    sequence contains no characters if the input string is empty or consists entirely of white
    space, or if the first non-white-space character is other than a sign or a permissible letter
    or digit.
5   If the subject sequence has the expected form and the value of base is zero, the sequence
    of characters starting with the first digit is interpreted as an integer constant according to
    the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
    is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
    as given above. If the subject sequence begins with a minus sign, the value resulting from
    the conversion is negated (in the return type). A pointer to the final string is stored in the
    object pointed to by endptr, provided that endptr is not a null pointer.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Returns
8   The strtol, strtoll, strtoul, and strtoull functions return the converted
    value, if any. If no conversion could be performed, zero is returned. If the correct value
    is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
    LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
    and sign of the value, if any), and the value of the macro ERANGE is stored in errno.

7.22.2 [Pseudo-random sequence generation functions]

 Pseudo-random sequence generation functions

7.22.2.1 [The rand function]


1           #include <stdlib.h>
            int rand(void);
    Description
2   The rand function computes a sequence of pseudo-random integers in the range 0 to
    RAND_MAX.295)
Footnote 295) There are no guarantees as to the quality of the random sequence produced and some implementations
         are known to produce sequences with distressingly non-random low-order bits. Applications with
         particular requirements should use a generator that is known to be sufficient for their needs.
3   The rand function is not required to avoid data races with other calls to pseudo-random
    sequence generation functions. The implementation shall behave as if no library function
    calls the rand function.
    Returns
4   The rand function returns a pseudo-random integer.
    Environmental limits
5   The value of the RAND_MAX macro shall be at least 32767.

7.22.2.2 [The srand function]


1           #include <stdlib.h>
            void srand(unsigned int seed);
    Description
2   The srand function uses the argument as a seed for a new sequence of pseudo-random
    numbers to be returned by subsequent calls to rand. If srand is then called with the
    same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
    called before any calls to srand have been made, the same sequence shall be generated
    as when srand is first called with a seed value of 1.
3   The srand function is not required to avoid data races with other calls to pseudo-
    random sequence generation functions. The implementation shall behave as if no library
    function calls the srand function.

    Returns
4   The srand function returns no value.
5   EXAMPLE     The following functions define a portable implementation of rand and srand.
            static unsigned long int next = 1;
            int rand(void)   // RAND_MAX assumed to be 32767
            {
                  next = next * 1103515245 + 12345;
                  return (unsigned int)(next/65536) % 32768;
            }
            void srand(unsigned int seed)
            {
                  next = seed;
            }


7.22.3 [Memory management functions]


1   The order and contiguity of storage allocated by successive calls to the
    aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
    pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
    a pointer to any type of object with a fundamental alignment requirement and then used
    to access such an object or an array of such objects in the space allocated (until the space
    is explicitly deallocated). The lifetime of an allocated object extends from the allocation
    until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
    any other object. The pointer returned points to the start (lowest byte address) of the
    allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
    the space requested is zero, the behavior is implementation-defined: either a null pointer
    is returned, or the behavior is as if the size were some nonzero value, except that the
    returned pointer shall not be used to access an object.
2   For purposes of determining the existence of a data race, memory allocation functions
    behave as though they accessed only memory locations accessible through their
    arguments and not other static duration storage. These functions may, however, visibly
    modify the storage that they allocate or deallocate. A call to free or realloc that
    deallocates a region p of memory synchronizes with any allocation call that allocates all
    or part of the region p. This synchronization occurs after any access of p by the
    deallocating function, and before any such access by the allocating function.

7.22.3.1 [The aligned_alloc function]


1           #include <stdlib.h>
            void *aligned_alloc(size_t alignment, size_t size);

    Description
2   The aligned_alloc function allocates space for an object whose alignment is
    specified by alignment, whose size is specified by size, and whose value is
    indeterminate. The value of alignment shall be a valid alignment supported by the
    implementation and the value of size shall be an integral multiple of alignment.
    Returns
3   The aligned_alloc function returns either a null pointer or a pointer to the allocated
    space.

7.22.3.2 [The calloc function]


1           #include <stdlib.h>
            void *calloc(size_t nmemb, size_t size);
    Description
2   The calloc function allocates space for an array of nmemb objects, each of whose size
    is size. The space is initialized to all bits zero.296)
    Returns
Footnote 296) Note that this need not be the same as the representation of floating-point zero or a null pointer
         constant.
3   The calloc function returns either a null pointer or a pointer to the allocated space.

7.22.3.3 [The free function]


1           #include <stdlib.h>
            void free(void *ptr);
    Description
2   The free function causes the space pointed to by ptr to be deallocated, that is, made
    available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
    the argument does not match a pointer earlier returned by a memory management
    function, or if the space has been deallocated by a call to free or realloc, the
    behavior is undefined.
    Returns
3   The free function returns no value.


7.22.3.4 [The malloc function]


1           #include <stdlib.h>
            void *malloc(size_t size);
    Description
2   The malloc function allocates space for an object whose size is specified by size and
    whose value is indeterminate.
    Returns
3   The malloc function returns either a null pointer or a pointer to the allocated space.

7.22.3.5 [The realloc function]


1           #include <stdlib.h>
            void *realloc(void *ptr, size_t size);
    Description
2   The realloc function deallocates the old object pointed to by ptr and returns a
    pointer to a new object that has the size specified by size. The contents of the new
    object shall be the same as that of the old object prior to deallocation, up to the lesser of
    the new and old sizes. Any bytes in the new object beyond the size of the old object have
    indeterminate values.
3   If ptr is a null pointer, the realloc function behaves like the malloc function for the
    specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
    management function, or if the space has been deallocated by a call to the free or
    realloc function, the behavior is undefined. If memory for the new object cannot be
    allocated, the old object is not deallocated and its value is unchanged.
    Returns
4   The realloc function returns a pointer to the new object (which may have the same
    value as a pointer to the old object), or a null pointer if the new object could not be
    allocated.

7.22.4 [Communication with the environment]

 Communication with the environment

7.22.4.1 [The abort function]


1          #include <stdlib.h>
           _Noreturn void abort(void);
    Description
2   The abort function causes abnormal program termination to occur, unless the signal
    SIGABRT is being caught and the signal handler does not return. Whether open streams
    with unwritten buffered data are flushed, open streams are closed, or temporary files are
    removed is implementation-defined. An implementation-defined form of the status
    unsuccessful termination is returned to the host environment by means of the function
    call raise(SIGABRT).
    Returns
3   The abort function does not return to its caller.

7.22.4.2 [The atexit function]


1          #include <stdlib.h>
           int atexit(void (*func)(void));
    Description
2   The atexit function registers the function pointed to by func, to be called without
    arguments at normal program termination.297) It is unspecified whether a call to the
    atexit function that does not happen before the exit function is called will succeed.
    Environmental limits
Footnote 297) The atexit function registrations are distinct from the at_quick_exit registrations, so
         applications may need to call both registration functions with the same argument.
3   The implementation shall support the registration of at least 32 functions.
    Returns
4   The atexit function returns zero if the registration succeeds, nonzero if it fails.
    Forward references: the at_quick_exit function (7.22.4.3), the exit function
    (7.22.4.4).


7.22.4.3 [The at_quick_exit function]


1           #include <stdlib.h>
            int at_quick_exit(void (*func)(void));
    Description
2   The at_quick_exit function registers the function pointed to by func, to be called
    without arguments should quick_exit be called.298) It is unspecified whether a call to
    the at_quick_exit function that does not happen before the quick_exit function
    is called will succeed.
    Environmental limits
Footnote 298) The at_quick_exit function registrations are distinct from the atexit registrations, so
         applications may need to call both registration functions with the same argument.
3   The implementation shall support the registration of at least 32 functions.
    Returns
4   The at_quick_exit function returns zero if the registration succeeds, nonzero if it
    fails.
    Forward references: the quick_exit function (7.22.4.7).

7.22.4.4 [The exit function]


1           #include <stdlib.h>
            _Noreturn void exit(int status);
    Description
2   The exit function causes normal program termination to occur. No functions registered
    by the at_quick_exit function are called. If a program calls the exit function
    more than once, or calls the quick_exit function in addition to the exit function, the
    behavior is undefined.
3   First, all functions registered by the atexit function are called, in the reverse order of
    their registration,299) except that a function is called after any previously registered
    functions that had already been called at the time it was registered. If, during the call to
    any such function, a call to the longjmp function is made that would terminate the call
    to the registered function, the behavior is undefined.

Footnote 299) Each function is called as many times as it was registered, and in the correct order with respect to
         other registered functions.
4   Next, all open streams with unwritten buffered data are flushed, all open streams are
    closed, and all files created by the tmpfile function are removed.
5   Finally, control is returned to the host environment. If the value of status is zero or
    EXIT_SUCCESS, an implementation-defined form of the status successful termination is
    returned. If the value of status is EXIT_FAILURE, an implementation-defined form
    of the status unsuccessful termination is returned. Otherwise the status returned is
    implementation-defined.
    Returns
6   The exit function cannot return to its caller.

7.22.4.5 [The _Exit function]


1           #include <stdlib.h>
            _Noreturn void _Exit(int status);
    Description
2   The _Exit function causes normal program termination to occur and control to be
    returned to the host environment. No functions registered by the atexit function, the
    at_quick_exit function, or signal handlers registered by the signal function are
    called. The status returned to the host environment is determined in the same way as for
    the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
    flushed, open streams are closed, or temporary files are removed is implementation-
    defined.
    Returns
3   The _Exit function cannot return to its caller.

7.22.4.6 [The getenv function]


1           #include <stdlib.h>
            char *getenv(const char *name);
    Description
2   The getenv function searches an environment list , provided by the host environment,
    for a string that matches the string pointed to by name. The set of environment names
    and the method for altering the environment list are implementation-defined. The
    getenv function need not avoid data races with other threads of execution that modify
    the environment list.300)

Footnote 300) Many implementations provide non-standard functions that modify the environment list.
3   The implementation shall behave as if no library function calls the getenv function.
    Returns
4   The getenv function returns a pointer to a string associated with the matched list
    member. The string pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the getenv function. If the specified name cannot
    be found, a null pointer is returned.

7.22.4.7 [The quick_exit function]


1           #include <stdlib.h>
            _Noreturn void quick_exit(int status);
    Description
2   The quick_exit function causes normal program termination to occur. No functions
    registered by the atexit function or signal handlers registered by the signal function
    are called. If a program calls the quick_exit function more than once, or calls the
    exit function in addition to the quick_exit function, the behavior is undefined. If a
    signal is raised while the quick_exit function is executing, the behavior is undefined.
3   The quick_exit function first calls all functions registered by the at_quick_exit
    function, in the reverse order of their registration,301) except that a function is called after
    any previously registered functions that had already been called at the time it was
    registered. If, during the call to any such function, a call to the longjmp function is
    made that would terminate the call to the registered function, the behavior is undefined.
Footnote 301) Each function is called as many times as it was registered, and in the correct order with respect to
         other registered functions.
4   Then control is returned to the host environment by means of the function call
    _Exit(status).
    Returns
5   The quick_exit function cannot return to its caller.

7.22.4.8 [The system function]


1           #include <stdlib.h>
            int system(const char *string);
    Description
2   If string is a null pointer, the system function determines whether the host
    environment has a command processor . If string is not a null pointer, the system

    function passes the string pointed to by string to that command processor to be
    executed in a manner which the implementation shall document; this might then cause the
    program calling system to behave in a non-conforming manner or to terminate.
    Returns
3   If the argument is a null pointer, the system function returns nonzero only if a
    command processor is available. If the argument is not a null pointer, and the system
    function does return, it returns an implementation-defined value.

7.22.5 [Searching and sorting utilities]


1   These utilities make use of a comparison function to search or sort arrays of unspecified
    type. Where an argument declared as size_t nmemb specifies the length of the array
    for a function, nmemb can have the value zero on a call to that function; the comparison
    function is not called, a search finds no matching element, and sorting performs no
    rearrangement. Pointer arguments on such a call shall still have valid values, as described
    in 7.1.4.
2   The implementation shall ensure that the second argument of the comparison function
    (when called from bsearch), or both arguments (when called from qsort), are
    pointers to elements of the array.302) The first argument when called from bsearch
    shall equal key.
Footnote 302) That is, if the value passed is p, then the following expressions are always nonzero:
                  ((char *)p - (char *)base) % size == 0
                  (char *)p >= (char *)base
                  (char *)p < (char *)base + nmemb * size
3   The comparison function shall not alter the contents of the array. The implementation
    may reorder elements of the array between calls to the comparison function, but shall not
    alter the contents of any individual element.
4   When the same objects (consisting of size bytes, irrespective of their current positions
    in the array) are passed more than once to the comparison function, the results shall be
    consistent with one another. That is, for qsort they shall define a total ordering on the
    array, and for bsearch the same object shall always compare the same way with the
    key.
5   A sequence point occurs immediately before and immediately after each call to the
    comparison function, and also between any call to the comparison function and any
    movement of the objects passed as arguments to that call.

7.22.5.1 [The bsearch function]


1            #include <stdlib.h>
             void *bsearch(const void *key, const void *base,
                  size_t nmemb, size_t size,
                  int (*compar)(const void *, const void *));
    Description
2   The bsearch function searches an array of nmemb objects, the initial element of which
    is pointed to by base, for an element that matches the object pointed to by key. The
    size of each element of the array is specified by size.
3   The comparison function pointed to by compar is called with two arguments that point
    to the key object and to an array element, in that order. The function shall return an
    integer less than, equal to, or greater than zero if the key object is considered,
    respectively, to be less than, to match, or to be greater than the array element. The array
    shall consist of: all the elements that compare less than, all the elements that compare
    equal to, and all the elements that compare greater than the key object, in that order.303)
    Returns
Footnote 303) In practice, the entire array is sorted according to the comparison function.
4   The bsearch function returns a pointer to a matching element of the array, or a null
    pointer if no match is found. If two elements compare as equal, which element is
    matched is unspecified.

7.22.5.2 [The qsort function]


1            #include <stdlib.h>
             void qsort(void *base, size_t nmemb, size_t size,
                  int (*compar)(const void *, const void *));
    Description
2   The qsort function sorts an array of nmemb objects, the initial element of which is
    pointed to by base. The size of each object is specified by size.
3   The contents of the array are sorted into ascending order according to a comparison
    function pointed to by compar, which is called with two arguments that point to the
    objects being compared. The function shall return an integer less than, equal to, or
    greater than zero if the first argument is considered to be respectively less than, equal to,
    or greater than the second.

4   If two elements compare as equal, their order in the resulting sorted array is unspecified.
    Returns
5   The qsort function returns no value.

7.22.6 [Integer arithmetic functions]

 Integer arithmetic functions

7.22.6.1 [The abs, labs and llabs functions]


1           #include <stdlib.h>
            int abs(int j);
            long int labs(long int j);
            long long int llabs(long long int j);
    Description
2   The abs, labs, and llabs functions compute the absolute value of an integer j. If the
    result cannot be represented, the behavior is undefined.304)
    Returns
Footnote 304) The absolute value of the most negative number cannot be represented in two's complement.
3   The abs, labs, and llabs, functions return the absolute value.

7.22.6.2 [The div, ldiv, and lldiv functions]


1           #include <stdlib.h>
            div_t div(int numer, int denom);
            ldiv_t ldiv(long int numer, long int denom);
            lldiv_t lldiv(long long int numer, long long int denom);
    Description
2   The div, ldiv, and lldiv, functions compute numer / denom and numer %
    denom in a single operation.
    Returns
3   The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
    lldiv_t, respectively, comprising both the quotient and the remainder. The structures
    shall contain (in either order) the members quot (the quotient) and rem (the remainder),
    each of which has the same type as the arguments numer and denom. If either part of
    the result cannot be represented, the behavior is undefined.


7.22.7 [Multibyte/wide character conversion functions]


1   The behavior of the multibyte character functions is affected by the LC_CTYPE category
    of the current locale. For a state-dependent encoding, each function is placed into its
    initial conversion state at program startup and can be returned to that state by a call for
    which its character pointer argument, s, is a null pointer. Subsequent calls with s as
    other than a null pointer cause the internal conversion state of the function to be altered as
    necessary. A call with s as a null pointer causes these functions to return a nonzero value
    if encodings have state dependency, and zero otherwise.305) Changing the LC_CTYPE
    category causes the conversion state of these functions to be indeterminate.
Footnote 305) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
         character codes, but are grouped with an adjacent multibyte character.

7.22.7.1 [The mblen function]


1           #include <stdlib.h>
            int mblen(const char *s, size_t n);
    Description
2   If s is not a null pointer, the mblen function determines the number of bytes contained
    in the multibyte character pointed to by s. Except that the conversion state of the
    mbtowc function is not affected, it is equivalent to
            mbtowc((wchar_t *)0, (const char *)0, 0);
            mbtowc((wchar_t *)0, s, n);
3   The implementation shall behave as if no library function calls the mblen function.
    Returns
4   If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the mblen function either returns 0 (if s points to the null character),
    or returns the number of bytes that are contained in the multibyte character (if the next n
    or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
    multibyte character).
    Forward references: the mbtowc function (7.22.7.2).


7.22.7.2 [The mbtowc function]


1          #include <stdlib.h>
           int mbtowc(wchar_t * restrict pwc,
                const char * restrict s,
                size_t n);
    Description
2   If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the value of the
    corresponding wide character and then, if pwc is not a null pointer, stores that value in
    the object pointed to by pwc. If the corresponding wide character is the null wide
    character, the function is left in the initial conversion state.
3   The implementation shall behave as if no library function calls the mbtowc function.
    Returns
4   If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
    or returns the number of bytes that are contained in the converted multibyte character (if
    the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
    form a valid multibyte character).
5   In no case will the value returned be greater than n or the value of the MB_CUR_MAX
    macro.

7.22.7.3 [The wctomb function]


1          #include <stdlib.h>
           int wctomb(char *s, wchar_t wc);
    Description
2   The wctomb function determines the number of bytes needed to represent the multibyte
    character corresponding to the wide character given by wc (including any shift
    sequences), and stores the multibyte character representation in the array whose first
    element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
    are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
    sequence needed to restore the initial shift state, and the function is left in the initial
    conversion state.

3   The implementation shall behave as if no library function calls the wctomb function.
    Returns
4   If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
    to a valid multibyte character, or returns the number of bytes that are contained in the
    multibyte character corresponding to the value of wc.
5   In no case will the value returned be greater than the value of the MB_CUR_MAX macro.

7.22.8 [Multibyte/wide string conversion functions]


1   The behavior of the multibyte string functions is affected by the LC_CTYPE category of
    the current locale.

7.22.8.1 [The mbstowcs function]


1            #include <stdlib.h>
             size_t mbstowcs(wchar_t * restrict pwcs,
                  const char * restrict s,
                  size_t n);
    Description
2   The mbstowcs function converts a sequence of multibyte characters that begins in the
    initial shift state from the array pointed to by s into a sequence of corresponding wide
    characters and stores not more than n wide characters into the array pointed to by pwcs.
    No multibyte characters that follow a null character (which is converted into a null wide
    character) will be examined or converted. Each multibyte character is converted as if by
    a call to the mbtowc function, except that the conversion state of the mbtowc function is
    not affected.
3   No more than n elements will be modified in the array pointed to by pwcs. If copying
    takes place between objects that overlap, the behavior is undefined.
    Returns
4   If an invalid multibyte character is encountered, the mbstowcs function returns
    (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
    elements modified, not including a terminating null wide character, if any.306)

Footnote 306) The array will not be null-terminated if the value returned is n.

7.22.8.2 [The wcstombs function]


1          #include <stdlib.h>
           size_t wcstombs(char * restrict s,
                const wchar_t * restrict pwcs,
                size_t n);
    Description
2   The wcstombs function converts a sequence of wide characters from the array pointed
    to by pwcs into a sequence of corresponding multibyte characters that begins in the
    initial shift state, and stores these multibyte characters into the array pointed to by s,
    stopping if a multibyte character would exceed the limit of n total bytes or if a null
    character is stored. Each wide character is converted as if by a call to the wctomb
    function, except that the conversion state of the wctomb function is not affected.
3   No more than n bytes will be modified in the array pointed to by s. If copying takes place
    between objects that overlap, the behavior is undefined.
    Returns
4   If a wide character is encountered that does not correspond to a valid multibyte character,
    the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
    returns the number of bytes modified, not including a terminating null character, if
    any.306)
Footnote 306) The array will not be null-terminated if the value returned is n.

7.23 [_Noreturn ]


1   The header <stdnoreturn.h> defines the macro
            noreturn
    which expands to _Noreturn.

7.24 [String handling ]

 String handling 

7.24.1 [String function conventions]


1   The header <string.h> declares one type and several functions, and defines one
    macro useful for manipulating arrays of character type and other objects treated as arrays
    of character type.307) The type is size_t and the macro is NULL (both described in
     7.19). Various methods are used for determining the lengths of the arrays, but in all cases
    a char * or void * argument points to the initial (lowest addressed) character of the
    array. If an array is accessed beyond the end of an object, the behavior is undefined.
Footnote 307) See ``future library directions'' (7.31.13).
2   Where an argument declared as size_t n specifies the length of the array for a
    function, n can have the value zero on a call to that function. Unless explicitly stated
    otherwise in the description of a particular function in this subclause, pointer arguments
    on such a call shall still have valid values, as described in 7.1.4. On such a call, a
    function that locates a character finds no occurrence, a function that compares two
    character sequences returns zero, and a function that copies characters copies zero
    characters.
3   For all functions in this subclause, each character shall be interpreted as if it had the type
    unsigned char (and therefore every possible object representation is valid and has a
    different value).

7.24.2 [Copying functions]

 Copying functions

7.24.2.1 [The memcpy function]


1            #include <string.h>
             void *memcpy(void * restrict s1,
                  const void * restrict s2,
                  size_t n);
    Description
2   The memcpy function copies n characters from the object pointed to by s2 into the
    object pointed to by s1. If copying takes place between objects that overlap, the behavior
    is undefined.
    Returns
3   The memcpy function returns the value of s1.


7.24.2.2 [The memmove function]


1           #include <string.h>
            void *memmove(void *s1, const void *s2, size_t n);
    Description
2   The memmove function copies n characters from the object pointed to by s2 into the
    object pointed to by s1. Copying takes place as if the n characters from the object
    pointed to by s2 are first copied into a temporary array of n characters that does not
    overlap the objects pointed to by s1 and s2, and then the n characters from the
    temporary array are copied into the object pointed to by s1.
    Returns
3   The memmove function returns the value of s1.

7.24.2.3 [The strcpy function]


1           #include <string.h>
            char *strcpy(char * restrict s1,
                 const char * restrict s2);
    Description
2   The strcpy function copies the string pointed to by s2 (including the terminating null
    character) into the array pointed to by s1. If copying takes place between objects that
    overlap, the behavior is undefined.
    Returns
3   The strcpy function returns the value of s1.

7.24.2.4 [The strncpy function]


1           #include <string.h>
            char *strncpy(char * restrict s1,
                 const char * restrict s2,
                 size_t n);
    Description
2   The strncpy function copies not more than n characters (characters that follow a null
    character are not copied) from the array pointed to by s2 to the array pointed to by
    s1.308) If copying takes place between objects that overlap, the behavior is undefined.
Footnote 308) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
         not be null-terminated.
3   If the array pointed to by s2 is a string that is shorter than n characters, null characters
    are appended to the copy in the array pointed to by s1, until n characters in all have been
    written.
    Returns
4   The strncpy function returns the value of s1.

7.24.3 [Concatenation functions]

 Concatenation functions

7.24.3.1 [The strcat function]


1            #include <string.h>
             char *strcat(char * restrict s1,
                  const char * restrict s2);
    Description
2   The strcat function appends a copy of the string pointed to by s2 (including the
    terminating null character) to the end of the string pointed to by s1. The initial character
    of s2 overwrites the null character at the end of s1. If copying takes place between
    objects that overlap, the behavior is undefined.
    Returns
3   The strcat function returns the value of s1.

7.24.3.2 [The strncat function]


1            #include <string.h>
             char *strncat(char * restrict s1,
                  const char * restrict s2,
                  size_t n);
    Description
2   The strncat function appends not more than n characters (a null character and
    characters that follow it are not appended) from the array pointed to by s2 to the end of
    the string pointed to by s1. The initial character of s2 overwrites the null character at the
    end of s1. A terminating null character is always appended to the result.309) If copying

    takes place between objects that overlap, the behavior is undefined.
    Returns
Footnote 309) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
         strlen(s1)+n+1.
3   The strncat function returns the value of s1.
    Forward references: the strlen function (7.24.6.3).

7.24.4 [Comparison functions]


1   The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
    and strncmp is determined by the sign of the difference between the values of the first
    pair of characters (both interpreted as unsigned char) that differ in the objects being
    compared.

7.24.4.1 [The memcmp function]


1           #include <string.h>
            int memcmp(const void *s1, const void *s2, size_t n);
    Description
2   The memcmp function compares the first n characters of the object pointed to by s1 to
    the first n characters of the object pointed to by s2.310)
    Returns
Footnote 310) The contents of ``holes'' used as padding for purposes of alignment within structure objects are
         indeterminate. Strings shorter than their allocated space and unions may also cause problems in
         comparison.
3   The memcmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
    pointed to by s2.

7.24.4.2 [The strcmp function]


1           #include <string.h>
            int strcmp(const char *s1, const char *s2);
    Description
2   The strcmp function compares the string pointed to by s1 to the string pointed to by
    s2.
    Returns
3   The strcmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the string pointed to by s1 is greater than, equal to, or less than the string

    pointed to by s2.

7.24.4.3 [The strcoll function]


1          #include <string.h>
           int strcoll(const char *s1, const char *s2);
    Description
2   The strcoll function compares the string pointed to by s1 to the string pointed to by
    s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
    Returns
3   The strcoll function returns an integer greater than, equal to, or less than zero,
    accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
    pointed to by s2 when both are interpreted as appropriate to the current locale.

7.24.4.4 [The strncmp function]


1          #include <string.h>
           int strncmp(const char *s1, const char *s2, size_t n);
    Description
2   The strncmp function compares not more than n characters (characters that follow a
    null character are not compared) from the array pointed to by s1 to the array pointed to
    by s2.
    Returns
3   The strncmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
    to, or less than the possibly null-terminated array pointed to by s2.

7.24.4.5 [The strxfrm function]


1          #include <string.h>
           size_t strxfrm(char * restrict s1,
                const char * restrict s2,
                size_t n);
    Description
2   The strxfrm function transforms the string pointed to by s2 and places the resulting
    string into the array pointed to by s1. The transformation is such that if the strcmp
    function is applied to two transformed strings, it returns a value greater than, equal to, or

    less than zero, corresponding to the result of the strcoll function applied to the same
    two original strings. No more than n characters are placed into the resulting array
    pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
    be a null pointer. If copying takes place between objects that overlap, the behavior is
    undefined.
    Returns
3   The strxfrm function returns the length of the transformed string (not including the
    terminating null character). If the value returned is n or more, the contents of the array
    pointed to by s1 are indeterminate.
4   EXAMPLE The value of the following expression is the size of the array needed to hold the
    transformation of the string pointed to by s.
            1 + strxfrm(NULL, s, 0)


7.24.5 [Search functions]

 Search functions

7.24.5.1 [The memchr function]


1           #include <string.h>
            void *memchr(const void *s, int c, size_t n);
    Description
2   The memchr function locates the first occurrence of c (converted to an unsigned
    char) in the initial n characters (each interpreted as unsigned char) of the object
    pointed to by s. The implementation shall behave as if it reads the characters sequentially
    and stops as soon as a matching character is found.
    Returns
3   The memchr function returns a pointer to the located character, or a null pointer if the
    character does not occur in the object.

7.24.5.2 [The strchr function]


1           #include <string.h>
            char *strchr(const char *s, int c);
    Description
2   The strchr function locates the first occurrence of c (converted to a char) in the
    string pointed to by s. The terminating null character is considered to be part of the
    string.

    Returns
3   The strchr function returns a pointer to the located character, or a null pointer if the
    character does not occur in the string.

7.24.5.3 [The strcspn function]


1          #include <string.h>
           size_t strcspn(const char *s1, const char *s2);
    Description
2   The strcspn function computes the length of the maximum initial segment of the string
    pointed to by s1 which consists entirely of characters not from the string pointed to by
    s2.
    Returns
3   The strcspn function returns the length of the segment.

7.24.5.4 [The strpbrk function]


1          #include <string.h>
           char *strpbrk(const char *s1, const char *s2);
    Description
2   The strpbrk function locates the first occurrence in the string pointed to by s1 of any
    character from the string pointed to by s2.
    Returns
3   The strpbrk function returns a pointer to the character, or a null pointer if no character
    from s2 occurs in s1.

7.24.5.5 [The strrchr function]


1          #include <string.h>
           char *strrchr(const char *s, int c);
    Description
2   The strrchr function locates the last occurrence of c (converted to a char) in the
    string pointed to by s. The terminating null character is considered to be part of the
    string.
    Returns
3   The strrchr function returns a pointer to the character, or a null pointer if c does not
    occur in the string.

7.24.5.6 [The strspn function]


1           #include <string.h>
            size_t strspn(const char *s1, const char *s2);
    Description
2   The strspn function computes the length of the maximum initial segment of the string
    pointed to by s1 which consists entirely of characters from the string pointed to by s2.
    Returns
3   The strspn function returns the length of the segment.

7.24.5.7 [The strstr function]


1           #include <string.h>
            char *strstr(const char *s1, const char *s2);
    Description
2   The strstr function locates the first occurrence in the string pointed to by s1 of the
    sequence of characters (excluding the terminating null character) in the string pointed to
    by s2.
    Returns
3   The strstr function returns a pointer to the located string, or a null pointer if the string
    is not found. If s2 points to a string with zero length, the function returns s1.

7.24.5.8 [The strtok function]


1           #include <string.h>
            char *strtok(char * restrict s1,
                 const char * restrict s2);
    Description
2   A sequence of calls to the strtok function breaks the string pointed to by s1 into a
    sequence of tokens, each of which is delimited by a character from the string pointed to
    by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
    sequence have a null first argument. The separator string pointed to by s2 may be
    different from call to call.
3   The first call in the sequence searches the string pointed to by s1 for the first character
    that is not contained in the current separator string pointed to by s2. If no such character
    is found, then there are no tokens in the string pointed to by s1 and the strtok function
    returns a null pointer. If such a character is found, it is the start of the first token.
4   The strtok function then searches from there for a character that is contained in the
    current separator string. If no such character is found, the current token extends to the
    end of the string pointed to by s1, and subsequent searches for a token will return a null
    pointer. If such a character is found, it is overwritten by a null character, which
    terminates the current token. The strtok function saves a pointer to the following
    character, from which the next search for a token will start.
5   Each subsequent call, with a null pointer as the value of the first argument, starts
    searching from the saved pointer and behaves as described above.
6   The strtok function is not required to avoid data races with other calls to the strtok
    function.311) The implementation shall behave as if no library function calls the strtok
    function.
    Returns
Footnote 311) The strtok_s function can be used instead to avoid data races.
7   The strtok function returns a pointer to the first character of a token, or a null pointer
    if there is no token.
8   EXAMPLE
            #include <string.h>
            static char str[] = "?a???b,,,#c";
            char *t;
            t   =   strtok(str, "?");         //   t   points to the token "a"
            t   =   strtok(NULL, ",");        //   t   points to the token "??b"
            t   =   strtok(NULL, "#,");       //   t   points to the token "c"
            t   =   strtok(NULL, "?");        //   t   is a null pointer

    Forward references: The strtok_s function (K.3.7.3.1).


7.24.6 [Miscellaneous functions]

 Miscellaneous functions

7.24.6.1 [The memset function]


1           #include <string.h>
            void *memset(void *s, int c, size_t n);
    Description
2   The memset function copies the value of c (converted to an unsigned char) into
    each of the first n characters of the object pointed to by s.
    Returns
3   The memset function returns the value of s.

7.24.6.2 [The strerror function]


1           #include <string.h>
            char *strerror(int errnum);
    Description
2   The strerror function maps the number in errnum to a message string. Typically,
    the values for errnum come from errno, but strerror shall map any value of type
    int to a message.
3   The strerror function is not required to avoid data races with other calls to the
    strerror function.312) The implementation shall behave as if no library function calls
    the strerror function.
    Returns
Footnote 312) The strerror_s function can be used instead to avoid data races.
4   The strerror function returns a pointer to the string, the contents of which are locale-
    specific. The array pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the strerror function.
    Forward references: The strerror_s function (K.3.7.4.2).


7.24.6.3 [The strlen function]


1          #include <string.h>
           size_t strlen(const char *s);
    Description
2   The strlen function computes the length of the string pointed to by s.
    Returns
3   The strlen function returns the number of characters that precede the terminating null
    character.

7.25 [Type-generic math ]


1   The header <tgmath.h> includes the headers <math.h> and <complex.h> and
    defines several type-generic macros.
2   Of the <math.h> and <complex.h> functions without an f (float) or l (long
    double) suffix, several have one or more parameters whose corresponding real type is
    double. For each such function, except modf, there is a corresponding type-generic
    macro.313) The parameters whose corresponding real type is double in the function
    synopsis are generic parameters. Use of the macro invokes a function whose
    corresponding real type and type domain are determined by the arguments for the generic
    parameters.314)
Footnote 313) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
         make available the corresponding ordinary function.
Footnote 314) If the type of the argument is not compatible with the type of the parameter for the selected function,
         the behavior is undefined.
3   Use of the macro invokes a function whose generic parameters have the corresponding
    real type determined as follows:
    -- First, if any argument for generic parameters has type long double, the type
       determined is long double.
    -- Otherwise, if any argument for generic parameters has type double or is of integer
       type, the type determined is double.
    -- Otherwise, the type determined is float.
4   For each unsuffixed function in <math.h> for which there is a function in
    <complex.h> with the same name except for a c prefix, the corresponding type-
    generic macro (for both functions) has the same name as the function in <math.h>. The
    corresponding type-generic macro for fabs and cabs is fabs.

            <math.h>          <complex.h>              type-generic
             function            function                 macro
             acos               cacos                    acos
             asin               casin                    asin
             atan               catan                    atan
             acosh              cacosh                   acosh
             asinh              casinh                   asinh
             atanh              catanh                   atanh
             cos                ccos                     cos
             sin                csin                     sin
             tan                ctan                     tan
             cosh               ccosh                    cosh
             sinh               csinh                    sinh
             tanh               ctanh                    tanh
             exp                cexp                     exp
             log                clog                     log
             pow                cpow                     pow
             sqrt               csqrt                    sqrt
             fabs               cabs                     fabs
    If at least one argument for a generic parameter is complex, then use of the macro invokes
    a complex function; otherwise, use of the macro invokes a real function.
5   For each unsuffixed function in <math.h> without a c-prefixed counterpart in
    <complex.h> (except modf), the corresponding type-generic macro has the same
    name as the function. These type-generic macros are:
          atan2                fma                  llround              remainder
          cbrt                 fmax                 log10                remquo
          ceil                 fmin                 log1p                rint
          copysign             fmod                 log2                 round
          erf                  frexp                logb                 scalbn
          erfc                 hypot                lrint                scalbln
          exp2                 ilogb                lround               tgamma
          expm1                ldexp                nearbyint            trunc
          fdim                 lgamma               nextafter
          floor                llrint               nexttoward
    If all arguments for generic parameters are real, then use of the macro invokes a real
    function; otherwise, use of the macro results in undefined behavior.
6   For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
    function in <math.h>, the corresponding type-generic macro has the same name as the
    function. These type-generic macros are:
            carg                    conj                     creal
            cimag                   cproj
    Use of the macro with any real or complex argument invokes a complex function.
7   EXAMPLE       With the declarations
            #include <tgmath.h>
            int n;
            float f;
            double d;
            long double ld;
            float complex fc;
            double complex dc;
            long double complex ldc;
    functions invoked by use of type-generic macros are shown in the following table:
                     macro use                                   invokes
                exp(n)                              exp(n), the function
                acosh(f)                            acoshf(f)
                sin(d)                              sin(d), the function
                atan(ld)                            atanl(ld)
                log(fc)                             clogf(fc)
                sqrt(dc)                            csqrt(dc)
                pow(ldc, f)                         cpowl(ldc, f)
                remainder(n, n)                     remainder(n, n), the function
                nextafter(d, f)                     nextafter(d, f), the function
                nexttoward(f, ld)                   nexttowardf(f, ld)
                copysign(n, ld)                     copysignl(n, ld)
                ceil(fc)                            undefined behavior
                rint(dc)                            undefined behavior
                fmax(ldc, ld)                       undefined behavior
                carg(n)                             carg(n), the function
                cproj(f)                            cprojf(f)
                creal(d)                            creal(d), the function
                cimag(ld)                           cimagl(ld)
                fabs(fc)                            cabsf(fc)
                carg(dc)                            carg(dc), the function
                cproj(ldc)                          cprojl(ldc)

7.26 [Threads ]

 Threads 

7.26.1 [Introduction]


1   The header <threads.h> includes the header <time.h>, defines macros, and
    declares types, enumeration constants, and functions that support multiple threads of
    execution.315)
Footnote 315) See ``future library directions'' (7.31.15).
2   Implementations that define the macro _ _STDC_NO_THREADS_ _ need not provide
    this header nor support any of its facilities.
3   The macros are
             thread_local
    which expands to _Thread_local;
             ONCE_FLAG_INIT
    which expands to a value that can be used to initialize an object of type once_flag;
    and
             TSS_DTOR_ITERATIONS
    which expands to an integer constant expression representing the maximum number of
    times that destructors will be called when a thread terminates.
4   The types are
             cnd_t
    which is a complete object type that holds an identifier for a condition variable;
             thrd_t
    which is a complete object type that holds an identifier for a thread;
             tss_t
    which is a complete object type that holds an identifier for a thread-specific storage
    pointer;
             mtx_t
    which is a complete object type that holds an identifier for a mutex;
             tss_dtor_t
    which is the function pointer type void (*)(void*), used for a destructor for a
    thread-specific storage pointer;

            thrd_start_t
    which is the function pointer type int (*)(void*) that is passed to thrd_create
    to create a new thread; and
              once_flag
    which is a complete object type that holds a flag for use by call_once.
5   The enumeration constants are
            mtx_plain
    which is passed to mtx_init to create a mutex object that supports neither timeout nor
    test and return;
              mtx_recursive
    which is passed to mtx_init to create a mutex object that supports recursive locking;
              mtx_timed
    which is passed to mtx_init to create a mutex object that supports timeout;
            thrd_timedout
    which is returned by a timed wait function to indicate that the time specified in the call
    was reached without acquiring the requested resource;
            thrd_success
    which is returned by a function to indicate that the requested operation succeeded;
            thrd_busy
    which is returned by a function to indicate that the requested operation failed because a
    resource requested by a test and return function is already in use;
            thrd_error
    which is returned by a function to indicate that the requested operation failed; and
            thrd_nomem
    which is returned by a function to indicate that the requested operation failed because it
    was unable to allocate memory.
    Forward references: date and time (7.27).

7.26.2 [Initialization functions]

 Initialization functions

7.26.2.1 [The call_once function]


1          #include <threads.h>
           void call_once(once_flag *flag, void (*func)(void));
    Description
2   The call_once function uses the once_flag pointed to by flag to ensure that
    func is called exactly once, the first time the call_once function is called with that
    value of flag. Completion of an effective call to the call_once function synchronizes
    with all subsequent calls to the call_once function with the same value of flag.
    Returns
3   The call_once function returns no value.

7.26.3 [Condition variable functions]

 Condition variable functions

7.26.3.1 [The cnd_broadcast function]


1          #include <threads.h>
           int cnd_broadcast(cnd_t *cond);
    Description
2   The cnd_broadcast function unblocks all of the threads that are blocked on the
    condition variable pointed to by cond at the time of the call. If no threads are blocked
    on the condition variable pointed to by cond at the time of the call, the function does
    nothing.
    Returns
3   The cnd_broadcast function returns thrd_success on success, or thrd_error
    if the request could not be honored.

7.26.3.2 [The cnd_destroy function]


1          #include <threads.h>
           void cnd_destroy(cnd_t *cond);
    Description
2   The cnd_destroy function releases all resources used by the condition variable
    pointed to by cond. The cnd_destroy function requires that no threads be blocked
    waiting for the condition variable pointed to by cond.

    Returns
3   The cnd_destroy function returns no value.

7.26.3.3 [The cnd_init function]


1           #include <threads.h>
            int cnd_init(cnd_t *cond);
    Description
2   The cnd_init function creates a condition variable. If it succeeds it sets the variable
    pointed to by cond to a value that uniquely identifies the newly created condition
    variable. A thread that calls cnd_wait on a newly created condition variable will
    block.
    Returns
3   The cnd_init function returns thrd_success on success, or thrd_nomem if no
    memory could be allocated for the newly created condition, or thrd_error if the
    request could not be honored.

7.26.3.4 [The cnd_signal function]


1           #include <threads.h>
            int cnd_signal(cnd_t *cond);
    Description
2   The cnd_signal function unblocks one of the threads that are blocked on the
    condition variable pointed to by cond at the time of the call. If no threads are blocked
    on the condition variable at the time of the call, the function does nothing and return
    success.
    Returns
3   The cnd_signal function returns thrd_success on success or thrd_error if
    the request could not be honored.

7.26.3.5 [The cnd_timedwait function]


1           #include <threads.h>
            int cnd_timedwait(cnd_t *restrict cond,
                 mtx_t *restrict mtx,
                 const struct timespec *restrict ts);
    Description
2   The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
    endeavors to block until the condition variable pointed to by cond is signaled by a call to
    cnd_signal or to cnd_broadcast, or until after the TIME_UTC-based calendar
    time pointed to by ts. When the calling thread becomes unblocked it locks the variable
    pointed to by mtx before it returns. The cnd_timedwait function requires that the
    mutex pointed to by mtx be locked by the calling thread.
    Returns
3   The cnd_timedwait function returns thrd_success upon success, or
    thrd_timedout if the time specified in the call was reached without acquiring the
    requested resource, or thrd_error if the request could not be honored.

7.26.3.6 [The cnd_wait function]


1          #include <threads.h>
           int cnd_wait(cnd_t *cond, mtx_t *mtx);
    Description
2   The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
    to block until the condition variable pointed to by cond is signaled by a call to
    cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
    locks the mutex pointed to by mtx before it returns. The cnd_wait function requires
    that the mutex pointed to by mtx be locked by the calling thread.
    Returns
3   The cnd_wait function returns thrd_success on success or thrd_error if the
    request could not be honored.

7.26.4 [Mutex functions]

 Mutex functions

7.26.4.1 [The mtx_destroy function]


1          #include <threads.h>
           void mtx_destroy(mtx_t *mtx);
    Description
2   The mtx_destroy function releases any resources used by the mutex pointed to by
    mtx. No threads can be blocked waiting for the mutex pointed to by mtx.
    Returns
3   The mtx_destroy function returns no value.


7.26.4.2 [The mtx_init function]


1           #include <threads.h>
            int mtx_init(mtx_t *mtx, int type);
    Description
2   The mtx_init function creates a mutex object with properties indicated by type,
    which must have one of the six values:
    mtx_plain for a simple non-recursive mutex,
    mtx_timed for a non-recursive mutex that supports timeout,                      
    mtx_plain | mtx_recursive for a simple recursive mutex, or
    mtx_timed | mtx_recursive for a recursive mutex that supports timeout.
3   If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
    uniquely identifies the newly created mutex.
    Returns
4   The mtx_init function returns thrd_success on success, or thrd_error if the
    request could not be honored.

7.26.4.3 [The mtx_lock function]


1           #include <threads.h>
            int mtx_lock(mtx_t *mtx);
    Description
2   The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
    is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
    on the same mutex shall synchronize with this operation.
    Returns
3   The mtx_lock function returns thrd_success on success, or thrd_error if the 
    request could not be honored.

7.26.4.4 [The mtx_timedlock function]


1           #include <threads.h>
            int mtx_timedlock(mtx_t *restrict mtx,
                 const struct timespec *restrict ts);
    Description
2   The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
    mtx or until after the TIME_UTC-based calendar time pointed to by ts. The specified
    mutex shall support timeout. If the operation succeeds, prior calls to mtx_unlock on
    the same mutex shall synchronize with this operation.
    Returns
3   The mtx_timedlock function returns thrd_success on success, or
    thrd_timedout if the time specified was reached without acquiring the requested
    resource, or thrd_error if the request could not be honored.

7.26.4.5 [The mtx_trylock function]


1          #include <threads.h>
           int mtx_trylock(mtx_t *mtx);
    Description
2   The mtx_trylock function endeavors to lock the mutex pointed to by mtx. If the 
    mutex is already locked, the function returns without blocking. If the operation succeeds,
    prior calls to mtx_unlock on the same mutex shall synchronize with this operation.
    Returns
3   The mtx_trylock function returns thrd_success on success, or thrd_busy if
    the resource requested is already in use, or thrd_error if the request could not be
    honored.

7.26.4.6 [The mtx_unlock function]


1          #include <threads.h>
           int mtx_unlock(mtx_t *mtx);
    Description
2   The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
    by mtx shall be locked by the calling thread.
    Returns
3   The mtx_unlock function returns thrd_success on success or thrd_error if
    the request could not be honored.

7.26.5 [Thread functions]

 Thread functions

7.26.5.1 [The thrd_create function]


1           #include <threads.h>
            int thrd_create(thrd_t *thr, thrd_start_t func,
                 void *arg);
    Description
2   The thrd_create function creates a new thread executing func(arg). If the
    thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
    the newly created thread. (A thread's identifier may be reused for a different thread once
    the original thread has exited and either been detached or joined to another thread.) The
    completion of the thrd_create function synchronizes with the beginning of the
    execution of the new thread.
    Returns
3   The thrd_create function returns thrd_success on success, or thrd_nomem if
    no memory could be allocated for the thread requested, or thrd_error if the request
    could not be honored.

7.26.5.2 [The thrd_current function]


1           #include <threads.h>
            thrd_t thrd_current(void);
    Description
2   The thrd_current function identifies the thread that called it.
    Returns
3   The thrd_current function returns the identifier of the thread that called it.

7.26.5.3 [The thrd_detach function]


1           #include <threads.h>
            int thrd_detach(thrd_t thr);
    Description
2   The thrd_detach function tells the operating system to dispose of any resources
    allocated to the thread identified by thr when that thread terminates. The thread
    identified by thr shall not have been previously detached or joined with another thread.
    Returns
3   The thrd_detach function returns thrd_success on success or thrd_error if
    the request could not be honored.

7.26.5.4 [The thrd_equal function]


1          #include <threads.h>
           int thrd_equal(thrd_t thr0, thrd_t thr1);
    Description
2   The thrd_equal function will determine whether the thread identified by thr0 refers
    to the thread identified by thr1.
    Returns
3   The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
    different threads. Otherwise the thrd_equal function returns a nonzero value.

7.26.5.5 [The thrd_exit function]


1          #include <threads.h>
           _Noreturn void thrd_exit(int res);
    Description
2   The thrd_exit function terminates execution of the calling thread and sets its result
    code to res.
3   The program shall terminate normally after the last thread has been terminated. The
    behavior shall be as if the program called the exit function with the status
    EXIT_SUCCESS at thread termination time.
    Returns
4   The thrd_exit function returns no value.

7.26.5.6 [The thrd_join function]


1          #include <threads.h>
           int thrd_join(thrd_t thr, int *res);
    Description
2   The thrd_join function joins the thread identified by thr with the current thread by
    blocking until the other thread has terminated. If the parameter res is not a null pointer,
    it stores the thread's result code in the integer pointed to by res. The termination of the

    other thread synchronizes with the completion of the thrd_join function. The thread
    identified by thr shall not have been previously detached or joined with another thread.
    Returns
3   The thrd_join function returns thrd_success on success or thrd_error if the
    request could not be honored.

7.26.5.7 [The thrd_sleep function]


1           #include <threads.h>
            int thrd_sleep(const struct timespec *duration,
                 struct timespec *remaining);
    Description
2   The thrd_sleep function suspends execution of the calling thread until either the
    interval specified by duration has elapsed or a signal which is not being ignored is
    received. If interrupted by a signal and the remaining argument is not null, the
    amount of time remaining (the requested interval minus the time actually slept) is stored
    in the interval it points to. The duration and remaining arguments may point to the
    same object.
3   The suspension time may be longer than requested because the interval is rounded up to
    an integer multiple of the sleep resolution or because of the scheduling of other activity
    by the system. But, except for the case of being interrupted by a signal, the suspension
    time shall not be less than that specified, as measured by the system clock TIME_UTC.
    Returns
4   The thrd_sleep function returns zero if the requested time has elapsed, -1 if it has
    been interrupted by a signal, or a negative value if it fails.

7.26.5.8 [The thrd_yield function]


1           #include <threads.h>
            void thrd_yield(void);
    Description
2   The thrd_yield function endeavors to permit other threads to run, even if the current
    thread would ordinarily continue to run.
    Returns
3   The thrd_yield function returns no value.


7.26.6 [Thread-specific storage functions]

 Thread-specific storage functions

7.26.6.1 [The tss_create function]


1          #include <threads.h>
           int tss_create(tss_t *key, tss_dtor_t dtor);
    Description
2   The tss_create function creates a thread-specific storage pointer with destructor
    dtor, which may be null.
    Returns
3   If the tss_create function is successful, it sets the thread-specific storage pointed to
    by key to a value that uniquely identifies the newly created pointer and returns
    thrd_success; otherwise, thrd_error is returned and the thread-specific storage
    pointed to by key is set to an undefined value.

7.26.6.2 [The tss_delete function]


1          #include <threads.h>
           void tss_delete(tss_t key);
    Description
2   The tss_delete function releases any resources used by the thread-specific storage
    identified by key.
    Returns
3   The tss_delete function returns no value.

7.26.6.3 [The tss_get function]


1          #include <threads.h>
           void *tss_get(tss_t key);
    Description
2   The tss_get function returns the value for the current thread held in the thread-specific
    storage identified by key.
    Returns
3   The tss_get function returns the value for the current thread if successful, or zero if
    unsuccessful.

7.26.6.4 [The tss_set function]


1           #include <threads.h>
            int tss_set(tss_t key, void *val);
    Description
2   The tss_set function sets the value for the current thread held in the thread-specific
    storage identified by key to val.
    Returns
3   The tss_set function returns thrd_success on success or thrd_error if the
    request could not be honored.                                             

7.27 [Date and time ]

 Date and time 

7.27.1 [Components of time]


1   The header <time.h> defines two macros, and declares several types and functions for
    manipulating time. Many functions deal with a calendar time that represents the current
    date (according to the Gregorian calendar) and time. Some functions deal with local
    time, which is the calendar time expressed for some specific time zone, and with Daylight
    Saving Time, which is a temporary change in the algorithm for determining local time.
    The local time zone and Daylight Saving Time are implementation-defined.
2   The macros defined are NULL (described in 7.19);                                                            
            CLOCKS_PER_SEC
    which expands to an expression with type clock_t (described below) that is the
    number per second of the value returned by the clock function; and
            TIME_UTC
    which expands to an integer constant greater than 0 that designates the UTC time
    base.316)
Footnote 316) Implementations may define additional time bases, but are only required to support a real time clock
         based on UTC.
3   The types declared are size_t (described in 7.19);
            clock_t
    and
            time_t
    which are real types capable of representing times;
            struct timespec
    which holds an interval specified in seconds and nanoseconds (which may represent a
    calendar time based on a particular epoch); and
            struct tm
    which holds the components of a calendar time, called the broken-down time.
4   The range and precision of times representable in clock_t and time_t are
    implementation-defined. The timespec structure shall contain at least the following
    members, in any order.317)

            time_t tv_sec; // whole seconds --  0
            long   tv_nsec; // nanoseconds -- [0, 999999999]
    The tm structure shall contain at least the following members, in any order. The
    semantics of the members and their normal ranges are expressed in the comments.318)
            int    tm_sec;           //   seconds after the minute -- [0, 60]
            int    tm_min;           //   minutes after the hour -- [0, 59]
            int    tm_hour;          //   hours since midnight -- [0, 23]
            int    tm_mday;          //   day of the month -- [1, 31]
            int    tm_mon;           //   months since January -- [0, 11]
            int    tm_year;          //   years since 1900
            int    tm_wday;          //   days since Sunday -- [0, 6]
            int    tm_yday;          //   days since January 1 -- [0, 365]
            int    tm_isdst;         //   Daylight Saving Time flag
    The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
    Saving Time is not in effect, and negative if the information is not available.
Footnote 317) The tv_sec member is a linear count of seconds and may not have the normal semantics of a
         time_t. The semantics of the members and their normal ranges are expressed in the comments.
Footnote 318) The range [0, 60] for tm_sec allows for a positive leap second.

7.27.2 [Time manipulation functions]

 Time manipulation functions

7.27.2.1 [The clock function]


1           #include <time.h>
            clock_t clock(void);
    Description
2   The clock function determines the processor time used.
    Returns
3   The clock function returns the implementation's best approximation to the processor
    time used by the program since the beginning of an implementation-defined era related
    only to the program invocation. To determine the time in seconds, the value returned by
    the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
    the processor time used is not available or its value cannot be represented, the function
    returns the value (clock_t)(-1).319)

Footnote 319) In order to measure the time spent in a program, the clock function should be called at the start of
         the program and its return value subtracted from the value returned by subsequent calls.

7.27.2.2 [The difftime function]


1           #include <time.h>
            double difftime(time_t time1, time_t time0);
    Description
2   The difftime function computes the difference between two calendar times: time1 -
    time0.
    Returns
3   The difftime function returns the difference expressed in seconds as a double.

7.27.2.3 [The mktime function]


1           #include <time.h>
            time_t mktime(struct tm *timeptr);
    Description
2   The mktime function converts the broken-down time, expressed as local time, in the
    structure pointed to by timeptr into a calendar time value with the same encoding as
    that of the values returned by the time function. The original values of the tm_wday
    and tm_yday components of the structure are ignored, and the original values of the
    other components are not restricted to the ranges indicated above.320) On successful
    completion, the values of the tm_wday and tm_yday components of the structure are
    set appropriately, and the other components are set to represent the specified calendar
    time, but with their values forced to the ranges indicated above; the final value of
    tm_mday is not set until tm_mon and tm_year are determined.
    Returns
Footnote 320) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
         Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
         causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.
3   The mktime function returns the specified calendar time encoded as a value of type
    time_t. If the calendar time cannot be represented, the function returns the value
    (time_t)(-1).
4   EXAMPLE       What day of the week is July 4, 2001?

            #include <stdio.h>
            #include <time.h>
            static const char *const wday[] = {
                    "Sunday", "Monday", "Tuesday", "Wednesday",
                    "Thursday", "Friday", "Saturday", "-unknown-"
            };
            struct tm time_str;
            /* ... */
            time_str.tm_year   = 2001 - 1900;
            time_str.tm_mon    = 7 - 1;
            time_str.tm_mday   = 4;
            time_str.tm_hour   = 0;
            time_str.tm_min    = 0;
            time_str.tm_sec    = 1;
            time_str.tm_isdst = -1;
            if (mktime(&time_str) == (time_t)(-1))
                  time_str.tm_wday = 7;
            printf("%s\n", wday[time_str.tm_wday]);


7.27.2.4 [The time function]


1           #include <time.h>
            time_t time(time_t *timer);
    Description
2   The time function determines the current calendar time. The encoding of the value is
    unspecified.
    Returns
3   The time function returns the implementation's best approximation to the current
    calendar time. The value (time_t)(-1) is returned if the calendar time is not
    available. If timer is not a null pointer, the return value is also assigned to the object it
    points to.

7.27.2.5 [The timespec_get function]


1           #include <time.h>
            int timespec_get(struct timespec *ts, int base);
    Description
2   The timespec_get function sets the interval pointed to by ts to hold the current
    calendar time based on the specified time base.
3   If base is TIME_UTC, the tv_sec member is set to the number of seconds since an
    implementation defined epoch, truncated to a whole value and the tv_nsec member is
    set to the integral number of nanoseconds, rounded to the resolution of the system
    clock.321)
    Returns
Footnote 321) Although a struct timespec object describes times with nanosecond resolution, the available
         resolution is system dependent and may even be greater than 1 second.
4   If the timespec_get function is successful it returns the nonzero value base;
    otherwise, it returns zero.

7.27.3 [Time conversion functions]


1   Except for the strftime function, these functions each return a pointer to one of two
    types of static objects: a broken-down time structure or an array of char. Execution of
    any of the functions that return a pointer to one of these object types may overwrite the
    information in any object of the same type pointed to by the value returned from any
    previous call to any of them and the functions are not required to avoid data races with
    each other.322) The implementation shall behave as if no other library functions call these
    functions.
Footnote 322) Alternative time conversion functions that do avoid data races are specified in K.3.8.2.

7.27.3.1 [The asctime function]


1            #include <time.h>
             char *asctime(const struct tm *timeptr);
    Description
2   The asctime function converts the broken-down time in the structure pointed to by
    timeptr into a string in the form
             Sun Sep 16 01:03:52 1973\n\0
    using the equivalent of the following algorithm.
    char *asctime(const struct tm *timeptr)
    {
         static const char wday_name[7][3] = {
              "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
         };
         static const char mon_name[12][3] = {
              "Jan", "Feb", "Mar", "Apr", "May", "Jun",
              "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
         };
         static char result[26];

            sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
                 wday_name[timeptr->tm_wday],
                 mon_name[timeptr->tm_mon],
                 timeptr->tm_mday, timeptr->tm_hour,
                 timeptr->tm_min, timeptr->tm_sec,
                 1900 + timeptr->tm_year);
            return result;
    }
3   If any of the members of the broken-down time contain values that are outside their
    normal ranges,323) the behavior of the asctime function is undefined. Likewise, if the
    calculated year exceeds four digits or is less than the year 1000, the behavior is
    undefined.
    Returns
Footnote 323) See 7.27.1.
4   The asctime function returns a pointer to the string.

7.27.3.2 [The ctime function]


1           #include <time.h>
            char *ctime(const time_t *timer);
    Description
2   The ctime function converts the calendar time pointed to by timer to local time in the
    form of a string. It is equivalent to
            asctime(localtime(timer))
    Returns
3   The ctime function returns the pointer returned by the asctime function with that
    broken-down time as argument.
    Forward references: the localtime function (7.27.3.4).

7.27.3.3 [The gmtime function]


1           #include <time.h>
            struct tm *gmtime(const time_t *timer);

    Description
2   The gmtime function converts the calendar time pointed to by timer into a broken-
    down time, expressed as UTC.
    Returns
3   The gmtime function returns a pointer to the broken-down time, or a null pointer if the
    specified time cannot be converted to UTC.

7.27.3.4 [The localtime function]


1          #include <time.h>
           struct tm *localtime(const time_t *timer);
    Description
2   The localtime function converts the calendar time pointed to by timer into a
    broken-down time, expressed as local time.
    Returns
3   The localtime function returns a pointer to the broken-down time, or a null pointer if
    the specified time cannot be converted to local time.

7.27.3.5 [The strftime function]


1          #include <time.h>
           size_t strftime(char * restrict s,
                size_t maxsize,
                const char * restrict format,
                const struct tm * restrict timeptr);
    Description
2   The strftime function places characters into the array pointed to by s as controlled by
    the string pointed to by format. The format shall be a multibyte character sequence,
    beginning and ending in its initial shift state. The format string consists of zero or
    more conversion specifiers and ordinary multibyte characters. A conversion specifier
    consists of a % character, possibly followed by an E or O modifier character (described
    below), followed by a character that determines the behavior of the conversion specifier.
    All ordinary multibyte characters (including the terminating null character) are copied
    unchanged into the array. If copying takes place between objects that overlap, the
    behavior is undefined. No more than maxsize characters are placed into the array.
3   Each conversion specifier is replaced by appropriate characters as described in the
    following list. The appropriate characters are determined using the LC_TIME category

of the current locale and by the values of zero or more members of the broken-down time
structure pointed to by timeptr, as specified in brackets in the description. If any of
the specified values is outside the normal range, the characters stored are unspecified.
%a   is replaced by the locale's abbreviated weekday name. [tm_wday]
%A   is replaced by the locale's full weekday name. [tm_wday]
%b   is replaced by the locale's abbreviated month name. [tm_mon]
%B   is replaced by the locale's full month name. [tm_mon]
%c   is replaced by the locale's appropriate date and time representation. [all specified
     in 7.27.1]
%C   is replaced by the year divided by 100 and truncated to an integer, as a decimal
     number (00-99). [tm_year]
%d   is replaced by the day of the month as a decimal number (01-31). [tm_mday]
%D   is equivalent to ``%m/%d/%y''. [tm_mon, tm_mday, tm_year]
%e   is replaced by the day of the month as a decimal number (1-31); a single digit is
     preceded by a space. [tm_mday]
%F   is equivalent to ``%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon,
     tm_mday]
%g   is replaced by the last 2 digits of the week-based year (see below) as a decimal
     number (00-99). [tm_year, tm_wday, tm_yday]
%G   is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
     [tm_year, tm_wday, tm_yday]
%h   is equivalent to ``%b''. [tm_mon]
%H   is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour]
%I   is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour]
%j   is replaced by the day of the year as a decimal number (001-366). [tm_yday]
%m   is replaced by the month as a decimal number (01-12). [tm_mon]
%M   is replaced by the minute as a decimal number (00-59). [tm_min]
%n   is replaced by a new-line character.
%p   is replaced by the locale's equivalent of the AM/PM designations associated with a
     12-hour clock. [tm_hour]
%r   is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec]
%R   is equivalent to ``%H:%M''. [tm_hour, tm_min]
%S   is replaced by the second as a decimal number (00-60). [tm_sec]
%t   is replaced by a horizontal-tab character.
%T   is equivalent to ``%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min,
     tm_sec]
%u   is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday
     is 1. [tm_wday]
%U   is replaced by the week number of the year (the first Sunday as the first day of week 1) 
     as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
%V   is replaced by the ISO 8601 week number (see below) as a decimal number
          (01-53). [tm_year, tm_wday, tm_yday]
    %w    is replaced by the weekday as a decimal number (0-6), where Sunday is 0.
          [tm_wday]
    %W    is replaced by the week number of the year (the first Monday as the first day of
          week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
    %x    is replaced by the locale's appropriate date representation. [all specified in 7.27.1]
    %X    is replaced by the locale's appropriate time representation. [all specified in 7.27.1]
    %y    is replaced by the last 2 digits of the year as a decimal number (00-99).
          [tm_year]
    %Y    is replaced by the year as a decimal number (e.g., 1997). [tm_year]
    %z    is replaced by the offset from UTC in the ISO 8601 format ``-0430'' (meaning 4
          hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
          zone is determinable. [tm_isdst]
    %Z    is replaced by the locale's time zone name or abbreviation, or by no characters if no
          time zone is determinable. [tm_isdst]
    %%    is replaced by %.
4   Some conversion specifiers can be modified by the inclusion of an E or O modifier
    character to indicate an alternative format or specification. If the alternative format or
    specification does not exist for the current locale, the modifier is ignored.
    %Ec is replaced by the locale's alternative date and time representation.
    %EC is replaced by the name of the base year (period) in the locale's alternative
        representation.
    %Ex is replaced by the locale's alternative date representation.
    %EX is replaced by the locale's alternative time representation.
    %Ey is replaced by the offset from %EC (year only) in the locale's alternative
        representation.
    %EY is replaced by the locale's full alternative year representation.
    %Od is replaced by the day of the month, using the locale's alternative numeric symbols
        (filled as needed with leading zeros, or with leading spaces if there is no alternative
        symbol for zero).
    %Oe is replaced by the day of the month, using the locale's alternative numeric symbols
        (filled as needed with leading spaces).
    %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric
        symbols.
    %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric
        symbols.
    %Om is replaced by the month, using the locale's alternative numeric symbols.
    %OM is replaced by the minutes, using the locale's alternative numeric symbols.
    %OS is replaced by the seconds, using the locale's alternative numeric symbols.
    %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative

        representation, where Monday is 1.
    %OU is replaced by the week number, using the locale's alternative numeric symbols.
    %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
        symbols.
    %Ow is replaced by the weekday as a number, using the locale's alternative numeric
        symbols.
    %OW is replaced by the week number of the year, using the locale's alternative numeric
        symbols.
    %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
        symbols.
5   %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
    weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
    which is also the week that includes the first Thursday of the year, and is also the first
    week that contains at least four days in the year. If the first Monday of January is the
    2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
    for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
    December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
    the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
    %V is replaced by 01.
6   If a conversion specifier is not one of the above, the behavior is undefined.
7   In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
    following specifiers are:
    %a    the first three characters of %A.
    %A    one of ``Sunday'', ``Monday'', ... , ``Saturday''.
    %b    the first three characters of %B.
    %B    one of ``January'', ``February'', ... , ``December''.
    %c    equivalent to ``%a %b %e %T %Y''.
    %p    one of ``AM'' or ``PM''.
    %r    equivalent to ``%I:%M:%S %p''.
    %x    equivalent to ``%m/%d/%y''.
    %X    equivalent to %T.
    %Z    implementation-defined.
    Returns
8   If the total number of resulting characters including the terminating null character is not
    more than maxsize, the strftime function returns the number of characters placed
    into the array pointed to by s not including the terminating null character. Otherwise,
    zero is returned and the contents of the array are indeterminate.


7.28 [Unicode utilities ]


1   The header <uchar.h> declares types and functions for manipulating Unicode
    characters.
2   The types declared are mbstate_t (described in 7.30.1) and size_t (described in 7.19);
           char16_t
    which is an unsigned integer type used for 16-bit characters and is the same type as
    uint_least16_t (described in 7.20.1.2); and
           char32_t
    which is an unsigned integer type used for 32-bit characters and is the same type as
    uint_least32_t (also described in 7.20.1.2).

7.28.1 [Restartable multibyte/wide character conversion functions]


1   These functions have a parameter, ps, of type pointer to mbstate_t that points to an
    object that can completely describe the current conversion state of the associated
    multibyte character sequence, which the functions alter as necessary. If ps is a null
    pointer, each function uses its own internal mbstate_t object instead, which is
    initialized at program startup to the initial conversion state; the functions are not required
    to avoid data races with other calls to the same function in this case. The implementation
    behaves as if no library function calls these functions with a null pointer for ps.

7.28.1.1 [The mbrtoc16 function]


1          #include <uchar.h>
           size_t mbrtoc16(char16_t * restrict pc16,
                const char * restrict s, size_t n,
                mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the mbrtoc16 function is equivalent to the call:
                   mbrtoc16(NULL, "", 1, ps)
    In this case, the values of the parameters pc16 and n are ignored.
3   If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the values of the
    corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
    the first (or only) such character in the object pointed to by pc16. Subsequent calls will
    store successive wide characters without consuming any additional input until all the
    characters have been stored. If the corresponding wide character is the null wide
    character, the resulting state described is the initial conversion state.
    Returns
4   The mbrtoc16 function returns the first of the following that applies (given the current
    conversion state):
    0                     if the next n or fewer bytes complete the multibyte character that
                          corresponds to the null wide character (which is the value stored).
    between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                       character (which is the value stored); the value returned is the number
                       of bytes that complete the multibyte character.
    (size_t)(-3) if the next character resulting from a previous call has been stored (no
                 bytes from the input have been consumed by this call).
    (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                 multibyte character, and all n bytes have been processed (no value is
                 stored).324)
    (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                 do not contribute to a complete and valid multibyte character (no
                 value is stored); the value of the macro EILSEQ is stored in errno,
                 and the conversion state is unspecified.
Footnote 324) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
         sequence of redundant shift sequences (for implementations with state-dependent encodings).

7.28.1.2 [The c16rtomb function]


1           #include <uchar.h>
            size_t c16rtomb(char * restrict s, char16_t c16,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the c16rtomb function is equivalent to the call
                    c16rtomb(buf, L'\0', ps)
    where buf is an internal buffer.
3   If s is not a null pointer, the c16rtomb function determines the number of bytes needed
    to represent the multibyte character that corresponds to the wide character given by c16
    (including any shift sequences), and stores the multibyte character representation in the

    array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
    c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
    to restore the initial shift state; the resulting state described is the initial conversion state.
    Returns
4   The c16rtomb function returns the number of bytes stored in the array object (including
    any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
    the function stores the value of the macro EILSEQ in errno and returns
    (size_t)(-1); the conversion state is unspecified.

7.28.1.3 [The mbrtoc32 function]


1           #include <uchar.h>
            size_t mbrtoc32(char32_t * restrict pc32,
                 const char * restrict s, size_t n,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the mbrtoc32 function is equivalent to the call:
                    mbrtoc32(NULL, "", 1, ps)
    In this case, the values of the parameters pc32 and n are ignored.
3   If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the values of the
    corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
    the first (or only) such character in the object pointed to by pc32. Subsequent calls will
    store successive wide characters without consuming any additional input until all the
    characters have been stored. If the corresponding wide character is the null wide
    character, the resulting state described is the initial conversion state.
    Returns
4   The mbrtoc32 function returns the first of the following that applies (given the current
    conversion state):
    0                    if the next n or fewer bytes complete the multibyte character that
                         corresponds to the null wide character (which is the value stored).
    between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                       character (which is the value stored); the value returned is the number
                       of bytes that complete the multibyte character.
    (size_t)(-3) if the next character resulting from a previous call has been stored (no
                 bytes from the input have been consumed by this call).
    (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                 multibyte character, and all n bytes have been processed (no value is
                 stored).325)
    (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                 do not contribute to a complete and valid multibyte character (no
                 value is stored); the value of the macro EILSEQ is stored in errno,
                 and the conversion state is unspecified.
Footnote 325) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
         sequence of redundant shift sequences (for implementations with state-dependent encodings).

7.28.1.4 [The c32rtomb function]


1           #include <uchar.h>
            size_t c32rtomb(char * restrict s, char32_t c32,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the c32rtomb function is equivalent to the call
                    c32rtomb(buf, L'\0', ps)
    where buf is an internal buffer.
3   If s is not a null pointer, the c32rtomb function determines the number of bytes needed
    to represent the multibyte character that corresponds to the wide character given by c32
    (including any shift sequences), and stores the multibyte character representation in the
    array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
    c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
    to restore the initial shift state; the resulting state described is the initial conversion state.
    Returns
4   The c32rtomb function returns the number of bytes stored in the array object (including
    any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
    the function stores the value of the macro EILSEQ in errno and returns
    (size_t)(-1); the conversion state is unspecified.


7.29 [Extended multibyte and wide character utilities ]

 Extended multibyte and wide character utilities 

7.29.1 [Introduction]


1   The header <wchar.h> defines four macros, and declares four data types, one tag, and
    many functions.326)
Footnote 326) See ``future library directions'' (7.31.16).
2   The types declared are wchar_t and size_t (both described in 7.19);
             mbstate_t
    which is a complete object type other than an array type that can hold the conversion state
    information necessary to convert between sequences of multibyte characters and wide
    characters;
             wint_t
    which is an integer type unchanged by default argument promotions that can hold any
    value corresponding to members of the extended character set, as well as at least one
    value that does not correspond to any member of the extended character set (see WEOF
    below);327) and
             struct tm
    which is declared as an incomplete structure type (the contents are described in 7.27.1).
Footnote 327) wchar_t and wint_t can be the same integer type.
3   The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
    (described in 7.20.3); and
             WEOF
    which expands to a constant expression of type wint_t whose value does not
    correspond to any member of the extended character set.328) It is accepted (and returned)
    by several functions in this subclause to indicate end-of-file, that is, no more input from a
    stream. It is also used as a wide character value that does not correspond to any member
    of the extended character set.
Footnote 328) The value of the macro WEOF may differ from that of EOF and need not be negative.
4   The functions declared are grouped as follows:
    -- Functions that perform input and output of wide characters, or multibyte characters,
       or both;
    -- Functions that provide wide string numeric conversion;
    -- Functions that perform general wide string manipulation;

    -- Functions for wide string date and time conversion; and
    -- Functions that provide extended capabilities for conversion between multibyte and
       wide character sequences.
5   Arguments to the functions in this subclause may point to arrays containing wchar_t
    values that do not correspond to members of the extended character set. Such values
    shall be processed according to the specified semantics, except that it is unspecified
    whether an encoding error occurs if such a value appears in the format string for a
    function in 7.29.2 or 7.29.5 and the specified semantics do not require that value to be
    processed by wcrtomb.
6   Unless explicitly stated otherwise, if the execution of a function described in this
    subclause causes copying to take place between objects that overlap, the behavior is
    undefined.

7.29.2 [Formatted wide character input/output functions]


1   The formatted wide character input/output functions shall behave as if there is a sequence
    point after the actions associated with each specifier.329)
Footnote 329) The fwprintf functions perform writes to memory for the %n specifier.

7.29.2.1 [The fwprintf function]


1           #include <stdio.h>
            #include <wchar.h>
            int fwprintf(FILE * restrict stream,
                 const wchar_t * restrict format, ...);
    Description
2   The fwprintf function writes output to the stream pointed to by stream, under
    control of the wide string pointed to by format that specifies how subsequent arguments
    are converted for output. If there are insufficient arguments for the format, the behavior
    is undefined. If the format is exhausted while arguments remain, the excess arguments
    are evaluated (as always) but are otherwise ignored. The fwprintf function returns
    when the end of the format string is encountered.
3   The format is composed of zero or more directives: ordinary wide characters (not %),
    which are copied unchanged to the output stream; and conversion specifications, each of
    which results in fetching zero or more subsequent arguments, converting them, if
    applicable, according to the corresponding conversion specifier, and then writing the
    result to the output stream.

4   Each conversion specification is introduced by the wide character %. After the %, the
    following appear in sequence:
    -- Zero or more flags (in any order) that modify the meaning of the conversion
       specification.
    -- An optional minimum field width. If the converted value has fewer wide characters
       than the field width, it is padded with spaces (by default) on the left (or right, if the
       left adjustment flag, described later, has been given) to the field width. The field
       width takes the form of an asterisk * (described later) or a nonnegative decimal
       integer.330)
    -- An optional precision that gives the minimum number of digits to appear for the d, i,
       o, u, x, and X conversions, the number of digits to appear after the decimal-point
       wide character for a, A, e, E, f, and F conversions, the maximum number of
       significant digits for the g and G conversions, or the maximum number of wide
       characters to be written for s conversions. The precision takes the form of a period
       (.) followed either by an asterisk * (described later) or by an optional decimal
       integer; if only the period is specified, the precision is taken as zero. If a precision
       appears with any other conversion specifier, the behavior is undefined.
    -- An optional length modifier that specifies the size of the argument.
    -- A conversion specifier wide character that specifies the type of conversion to be
       applied.
Footnote 330) Note that 0 is taken as a flag, not as the beginning of a field width.
5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
    this case, an int argument supplies the field width or precision. The arguments
    specifying field width, or precision, or both, shall appear (in that order) before the
    argument (if any) to be converted. A negative field width argument is taken as a - flag
    followed by a positive field width. A negative precision argument is taken as if the
    precision were omitted.
6   The flag wide characters and their meanings are:
    -        The result of the conversion is left-justified within the field. (It is right-justified if
             this flag is not specified.)
    +        The result of a signed conversion always begins with a plus or minus sign. (It
             begins with a sign only when a negative value is converted if this flag is not

              specified.)331)
    space If the first wide character of a signed conversion is not a sign, or if a signed
          conversion results in no wide characters, a space is prefixed to the result. If the
          space and + flags both appear, the space flag is ignored.
    #         The result is converted to an ``alternative form''. For o conversion, it increases
              the precision, if and only if necessary, to force the first digit of the result to be a
              zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
              conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
              and G conversions, the result of converting a floating-point number always
              contains a decimal-point wide character, even if no digits follow it. (Normally, a
              decimal-point wide character appears in the result of these conversions only if a
              digit follows it.) For g and G conversions, trailing zeros are not removed from the
              result. For other conversions, the behavior is undefined.
    0         For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
              (following any indication of sign or base) are used to pad to the field width rather
              than performing space padding, except when converting an infinity or NaN. If the
              0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
              conversions, if a precision is specified, the 0 flag is ignored. For other
              conversions, the behavior is undefined.
Footnote 331) The results of all floating conversions of a negative zero, and of negative values that round to zero,
         include a minus sign.
7   The length modifiers and their meanings are:
    hh             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   signed char or unsigned char argument (the argument will have
                   been promoted according to the integer promotions, but its value shall be
                   converted to signed char or unsigned char before printing); or that
                   a following n conversion specifier applies to a pointer to a signed char
                   argument.
    h              Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   short int or unsigned short int argument (the argument will
                   have been promoted according to the integer promotions, but its value shall
                   be converted to short int or unsigned short int before printing);
                   or that a following n conversion specifier applies to a pointer to a short
                   int argument.
    l (ell)        Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   long int or unsigned long int argument; that a following n
                   conversion specifier applies to a pointer to a long int argument; that a

                 following c conversion specifier applies to a wint_t argument; that a
                 following s conversion specifier applies to a pointer to a wchar_t
                 argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                 specifier.
    ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 long long int or unsigned long long int argument; or that a
                 following n conversion specifier applies to a pointer to a long long int
                 argument.
    j            Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                 an intmax_t or uintmax_t argument; or that a following n conversion
                 specifier applies to a pointer to an intmax_t argument.
    z            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 size_t or the corresponding signed integer type argument; or that a
                 following n conversion specifier applies to a pointer to a signed integer type
                 corresponding to size_t argument.
    t            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 ptrdiff_t or the corresponding unsigned integer type argument; or that a
                 following n conversion specifier applies to a pointer to a ptrdiff_t
                 argument.
    L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                 applies to a long double argument.
        If a length modifier appears with any conversion specifier other than as specified above,
        the behavior is undefined.
8   The conversion specifiers and their meanings are:
    d,i         The int argument is converted to signed decimal in the style [-]dddd. The
                precision specifies the minimum number of digits to appear; if the value
                being converted can be represented in fewer digits, it is expanded with
                leading zeros. The default precision is 1. The result of converting a zero
                value with a precision of zero is no wide characters.
        o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
                decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd ; the
                letters abcdef are used for x conversion and the letters ABCDEF for X
                conversion. The precision specifies the minimum number of digits to appear;
                if the value being converted can be represented in fewer digits, it is expanded
                with leading zeros. The default precision is 1. The result of converting a
                zero value with a precision of zero is no wide characters.

    f,F          A double argument representing a floating-point number is converted to
                 decimal notation in the style [-]ddd.ddd, where the number of digits after
                 the decimal-point wide character is equal to the precision specification. If the
                 precision is missing, it is taken as 6; if the precision is zero and the # flag is
                 not specified, no decimal-point wide character appears. If a decimal-point
                 wide character appears, at least one digit appears before it. The value is
                 rounded to the appropriate number of digits.
                 A double argument representing an infinity is converted in one of the styles
                 [-]inf or [-]infinity -- which style is implementation-defined. A
                 double argument representing a NaN is converted in one of the styles
                 [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
                 any n-wchar-sequence, is implementation-defined. The F conversion
                 specifier produces INF, INFINITY, or NAN instead of inf, infinity, or
                 nan, respectively.332)
    e,E          A double argument representing a floating-point number is converted in the
                 style [-]d.ddd e±dd, where there is one digit (which is nonzero if the
                 argument is nonzero) before the decimal-point wide character and the number
                 of digits after it is equal to the precision; if the precision is missing, it is taken
                 as 6; if the precision is zero and the # flag is not specified, no decimal-point
                 wide character appears. The value is rounded to the appropriate number of
                 digits. The E conversion specifier produces a number with E instead of e
                 introducing the exponent. The exponent always contains at least two digits,
                 and only as many more digits as necessary to represent the exponent. If the
                 value is zero, the exponent is zero.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    g,G          A double argument representing a floating-point number is converted in
                 style f or e (or in style F or E in the case of a G conversion specifier),
                 depending on the value converted and the precision. Let P equal the
                 precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
                 Then, if a conversion with style E would have an exponent of X :
                 -- if P > X  -4, the conversion is with style f (or F) and precision
                    P - ( X + 1).
                 -- otherwise, the conversion is with style e (or E) and precision P - 1.
                 Finally, unless the # flag is used, any trailing zeros are removed from the

                 fractional portion of the result and the decimal-point wide character is
                 removed if there is no fractional portion remaining.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    a,A          A double argument representing a floating-point number is converted in the
                 style [-]0xh.hhhh p±d, where there is one hexadecimal digit (which is
                 nonzero if the argument is a normalized floating-point number and is
                 otherwise unspecified) before the decimal-point wide character333) and the
                 number of hexadecimal digits after it is equal to the precision; if the precision
                 is missing and FLT_RADIX is a power of 2, then the precision is sufficient
                 for an exact representation of the value; if the precision is missing and
                 FLT_RADIX is not a power of 2, then the precision is sufficient to
                 distinguish334) values of type double, except that trailing zeros may be
                 omitted; if the precision is zero and the # flag is not specified, no decimal-
                 point wide character appears. The letters abcdef are used for a conversion
                 and the letters ABCDEF for A conversion. The A conversion specifier
                 produces a number with X and P instead of x and p. The exponent always
                 contains at least one digit, and only as many more digits as necessary to
                 represent the decimal exponent of 2. If the value is zero, the exponent is
                 zero.
                 A double argument representing an infinity or NaN is converted in the style
                 of an f or F conversion specifier.
    c            If no l length modifier is present, the int argument is converted to a wide
                 character as if by calling btowc and the resulting wide character is written.
                 If an l length modifier is present, the wint_t argument is converted to
                 wchar_t and written.
    s            If no l length modifier is present, the argument shall be a pointer to the initial
                 element of a character array containing a multibyte character sequence
                 beginning in the initial shift state. Characters from the array are converted as
                 if by repeated calls to the mbrtowc function, with the conversion state
                 described by an mbstate_t object initialized to zero before the first
                 multibyte character is converted, and written up to (but not including) the

                    terminating null wide character. If the precision is specified, no more than
                    that many wide characters are written. If the precision is not specified or is
                    greater than the size of the converted array, the converted array shall contain a
                    null wide character.
                    If an l length modifier is present, the argument shall be a pointer to the initial
                    element of an array of wchar_t type. Wide characters from the array are
                    written up to (but not including) a terminating null wide character. If the
                    precision is specified, no more than that many wide characters are written. If
                    the precision is not specified or is greater than the size of the array, the array
                    shall contain a null wide character.
     p              The argument shall be a pointer to void. The value of the pointer is
                    converted to a sequence of printing wide characters, in an implementation-
                    defined manner.
     n              The argument shall be a pointer to signed integer into which is written the
                    number of wide characters written to the output stream so far by this call to
                    fwprintf. No argument is converted, but one is consumed. If the
                    conversion specification includes any flags, a field width, or a precision, the
                    behavior is undefined.
     %              A % wide character is written. No argument is converted. The complete
                    conversion specification shall be %%.
Footnote 332) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
         meaning; the # and 0 flag wide characters have no effect.
Footnote 333) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
         character so that subsequent digits align to nibble (4-bit) boundaries.
Footnote 334) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
         FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
         might suffice depending on the implementation's scheme for determining the digit to the left of the
         decimal-point wide character.
9    If a conversion specification is invalid, the behavior is undefined.335) If any argument is
     not the correct type for the corresponding conversion specification, the behavior is
     undefined.
Footnote 335) See ``future library directions'' (7.31.16).
10   In no case does a nonexistent or small field width cause truncation of a field; if the result
     of a conversion is wider than the field width, the field is expanded to contain the
     conversion result.
11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
     to a hexadecimal floating number with the given precision.
     Recommended practice
12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
     representable in the given precision, the result should be one of the two adjacent numbers
     in hexadecimal floating style with the given precision, with the extra stipulation that the
     error should have a correct sign for the current rounding direction.
13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
     DECIMAL_DIG, then the result should be correctly rounded.336) If the number of

     significant decimal digits is more than DECIMAL_DIG but the source value is exactly
     representable with DECIMAL_DIG digits, then the result should be an exact
     representation with trailing zeros. Otherwise, the source value is bounded by two
     adjacent decimal strings L < U , both having DECIMAL_DIG significant digits; the value
     of the resultant decimal string D should satisfy L  D  U , with the extra stipulation that
     the error should have a correct sign for the current rounding direction.
     Returns
Footnote 336) For binary-to-decimal conversion, the result format's values are the numbers representable with the
          given format specifier. The number of significant digits is determined by the format specifier, and in
          the case of fixed-point conversion by the source value as well.
14   The fwprintf function returns the number of wide characters transmitted, or a negative
     value if an output or encoding error occurred.
     Environmental limits
15   The number of wide characters that can be produced by any single conversion shall be at
     least 4095.
16   EXAMPLE       To print a date and time in the form ``Sunday, July 3, 10:02'' followed by  to five decimal
     places:
             #include <math.h>
             #include <stdio.h>
             #include <wchar.h>
             /* ... */
             wchar_t *weekday, *month; // pointers to wide strings
             int day, hour, min;
             fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
                     weekday, month, day, hour, min);
             fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));

     Forward references:           the btowc function (7.29.6.1.1), the mbrtowc function
     (7.29.6.3.2).

7.29.2.2 [The fwscanf function]


1            #include <stdio.h>
             #include <wchar.h>
             int fwscanf(FILE * restrict stream,
                  const wchar_t * restrict format, ...);
     Description
2    The fwscanf function reads input from the stream pointed to by stream, under
     control of the wide string pointed to by format that specifies the admissible input
     sequences and how they are to be converted for assignment, using subsequent arguments

    as pointers to the objects to receive the converted input. If there are insufficient
    arguments for the format, the behavior is undefined. If the format is exhausted while
    arguments remain, the excess arguments are evaluated (as always) but are otherwise
    ignored.
3   The format is composed of zero or more directives: one or more white-space wide
    characters, an ordinary wide character (neither % nor a white-space wide character), or a
    conversion specification. Each conversion specification is introduced by the wide
    character %. After the %, the following appear in sequence:
    -- An optional assignment-suppressing wide character *.
    -- An optional decimal integer greater than zero that specifies the maximum field width
       (in wide characters).
    -- An optional length modifier that specifies the size of the receiving object.
    -- A conversion specifier wide character that specifies the type of conversion to be
       applied.
4   The fwscanf function executes each directive of the format in turn. When all directives
    have been executed, or if a directive fails (as detailed below), the function returns.
    Failures are described as input failures (due to the occurrence of an encoding error or the
    unavailability of input characters), or matching failures (due to inappropriate input).
5   A directive composed of white-space wide character(s) is executed by reading input up to
    the first non-white-space wide character (which remains unread), or until no more wide
    characters can be read. The directive never fails.
6   A directive that is an ordinary wide character is executed by reading the next wide
    character of the stream. If that wide character differs from the directive, the directive
    fails and the differing and subsequent wide characters remain unread. Similarly, if end-
    of-file, an encoding error, or a read error prevents a wide character from being read, the
    directive fails.
7   A directive that is a conversion specification defines a set of matching input sequences, as
    described below for each specifier. A conversion specification is executed in the
    following steps:
8   Input white-space wide characters (as specified by the iswspace function) are skipped,
    unless the specification includes a [, c, or n specifier.337)
Footnote 337) These white-space wide characters are not counted against a specified field width.
9   An input item is read from the stream, unless the specification includes an n specifier. An
    input item is defined as the longest sequence of input wide characters which does not
    exceed any specified field width and which is, or is a prefix of, a matching input

     sequence.338) The first wide character, if any, after the input item remains unread. If the
     length of the input item is zero, the execution of the directive fails; this condition is a
     matching failure unless end-of-file, an encoding error, or a read error prevented input
     from the stream, in which case it is an input failure.
Footnote 338) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
          sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.
10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
     count of input wide characters) is converted to a type appropriate to the conversion
     specifier. If the input item is not a matching sequence, the execution of the directive fails:
     this condition is a matching failure. Unless assignment suppression was indicated by a *,
     the result of the conversion is placed in the object pointed to by the first argument
     following the format argument that has not already received a conversion result. If this
     object does not have an appropriate type, or if the result of the conversion cannot be
     represented in the object, the behavior is undefined.
11   The length modifiers and their meanings are:
     hh           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to signed char or unsigned char.
     h            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to short int or unsigned short
                  int.
     l (ell)      Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long int or unsigned long
                  int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                  an argument with type pointer to double; or that a following c, s, or [
                  conversion specifier applies to an argument with type pointer to wchar_t.
     ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long long int or unsigned
                  long long int.
     j            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to intmax_t or uintmax_t.
     z            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to size_t or the corresponding signed
                  integer type.
     t            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to ptrdiff_t or the corresponding
                  unsigned integer type.

     L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                  applies to an argument with type pointer to long double.
     If a length modifier appears with any conversion specifier other than as specified above,
     the behavior is undefined.
12   The conversion specifiers and their meanings are:
     d           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the wcstol function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 signed integer.
     i           Matches an optionally signed integer, whose format is the same as expected
                 for the subject sequence of the wcstol function with the value 0 for the
                 base argument. The corresponding argument shall be a pointer to signed
                 integer.
     o           Matches an optionally signed octal integer, whose format is the same as
                 expected for the subject sequence of the wcstoul function with the value 8
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     u           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the wcstoul function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     x           Matches an optionally signed hexadecimal integer, whose format is the same
                 as expected for the subject sequence of the wcstoul function with the value
                 16 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
             format is the same as expected for the subject sequence of the wcstod
             function. The corresponding argument shall be a pointer to floating.
     c           Matches a sequence of wide characters of exactly the number specified by the
                 field width (1 if no field width is present in the directive).
                 If no l length modifier is present, characters from the input field are
                 converted as if by repeated calls to the wcrtomb function, with the
                 conversion state described by an mbstate_t object initialized to zero
                 before the first wide character is converted. The corresponding argument
                 shall be a pointer to the initial element of a character array large enough to
                 accept the sequence. No null character is added.
                 If an l length modifier is present, the corresponding argument shall be a
             pointer to the initial element of an array of wchar_t large enough to accept
             the sequence. No null wide character is added.
    s        Matches a sequence of non-white-space wide characters.
             If no l length modifier is present, characters from the input field are
             converted as if by repeated calls to the wcrtomb function, with the
             conversion state described by an mbstate_t object initialized to zero
             before the first wide character is converted. The corresponding argument
             shall be a pointer to the initial element of a character array large enough to
             accept the sequence and a terminating null character, which will be added
             automatically.
             If an l length modifier is present, the corresponding argument shall be a
             pointer to the initial element of an array of wchar_t large enough to accept
             the sequence and the terminating null wide character, which will be added
             automatically.
    [        Matches a nonempty sequence of wide characters from a set of expected
             characters (the scanset ).
             
             If no l length modifier is present, characters from the input field are
             converted as if by repeated calls to the wcrtomb function, with the
             conversion state described by an mbstate_t object initialized to zero
             before the first wide character is converted. The corresponding argument
             shall be a pointer to the initial element of a character array large enough to
             accept the sequence and a terminating null character, which will be added
             automatically.
             
             If an l length modifier is present, the corresponding argument shall be a
             pointer to the initial element of an array of wchar_t large enough to accept
             the sequence and the terminating null wide character, which will be added
             automatically.

             The conversion specifier includes all subsequent wide characters in the
             format string, up to and including the matching right bracket (]). The wide
             characters between the brackets (the scanlist ) compose the scanset, unless the
             wide character after the left bracket is a circumflex (^), in which case the
             scanset contains all wide characters that do not appear in the scanlist between
             the circumflex and the right bracket. If the conversion specifier begins with
             [] or [^], the right bracket wide character is in the scanlist and the next
             following right bracket wide character is the matching right bracket that ends
             the specification; otherwise the first following right bracket wide character is
             the one that ends the specification. If a - wide character is in the scanlist and
             is not the first, nor the second where the first wide character is a ^, nor the
             last character, the behavior is implementation-defined.
     p              Matches an implementation-defined set of sequences, which should be the
                    same as the set of sequences that may be produced by the %p conversion of
                    the fwprintf function. The corresponding argument shall be a pointer to a
                    pointer to void. The input item is converted to a pointer value in an
                    implementation-defined manner. If the input item is a value converted earlier
                    during the same program execution, the pointer that results shall compare
                    equal to that value; otherwise the behavior of the %p conversion is undefined.
     n              No input is consumed. The corresponding argument shall be a pointer to
                    signed integer into which is to be written the number of wide characters read
                    from the input stream so far by this call to the fwscanf function. Execution
                    of a %n directive does not increment the assignment count returned at the
                    completion of execution of the fwscanf function. No argument is
                    converted, but one is consumed. If the conversion specification includes an
                    assignment-suppressing wide character or a field width, the behavior is
                    undefined.
     %              Matches a single % wide character; no conversion or assignment occurs. The
                    complete conversion specification shall be %%.
13   If a conversion specification is invalid, the behavior is undefined.339)
Footnote 339) See ``future library directions'' (7.31.16).
14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
     respectively, a, e, f, g, and x.
15   Trailing white space (including new-line wide characters) is left unread unless matched
     by a directive. The success of literal matches and suppressed assignments is not directly
     determinable other than via the %n directive.
     Returns
16   The fwscanf function returns the value of the macro EOF if an input failure occurs
     before the first conversion (if any) has completed. Otherwise, the function returns the
     number of input items assigned, which can be fewer than provided for, or even zero, in
     the event of an early matching failure.
17   EXAMPLE 1       The call:
              #include <stdio.h>
              #include <wchar.h>
              /* ... */
              int n, i; float x; wchar_t name[50];
              n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);

     with the input line:
              25 54.32E-1 thompson
     will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
     thompson\0.

18   EXAMPLE 2        The call:
              #include <stdio.h>
              #include <wchar.h>
              /* ... */
              int i; float x; double y;
              fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
     with input:
              56789 0123 56a72
     will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value
     56.0. The next wide character read from the input stream will be a.

     Forward references: the wcstod, wcstof, and wcstold functions (7.29.4.1.1), the
     wcstol, wcstoll, wcstoul, and wcstoull functions (7.29.4.1.2), the wcrtomb
     function (7.29.6.3.3).

7.29.2.3 [The swprintf function]


1             #include <wchar.h>
              int swprintf(wchar_t * restrict s,
                   size_t n,
                   const wchar_t * restrict format, ...);
     Description
2    The swprintf function is equivalent to fwprintf, except that the argument s
     specifies an array of wide characters into which the generated output is to be written,
     rather than written to a stream. No more than n wide characters are written, including a
     terminating null wide character, which is always added (unless n is zero).
     Returns
3    The swprintf function returns the number of wide characters written in the array, not
     counting the terminating null wide character, or a negative value if an encoding error
     occurred or if n or more wide characters were requested to be written.

7.29.2.4 [The swscanf function]


1           #include <wchar.h>
            int swscanf(const wchar_t * restrict s,
                 const wchar_t * restrict format, ...);
    Description
2   The swscanf function is equivalent to fwscanf, except that the argument s specifies a
    wide string from which the input is to be obtained, rather than from a stream. Reaching
    the end of the wide string is equivalent to encountering end-of-file for the fwscanf
    function.
    Returns
3   The swscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the swscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.29.2.5 [The vfwprintf function]


1           #include <stdarg.h>
            #include <stdio.h>
            #include <wchar.h>
            int vfwprintf(FILE * restrict stream,
                 const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vfwprintf function is equivalent to fwprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfwprintf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vfwprintf function returns the number of wide characters transmitted, or a
    negative value if an output or encoding error occurred.

4   EXAMPLE       The following shows the use of the vfwprintf function in a general error-reporting
    routine.
           #include <stdarg.h>
           #include <stdio.h>
           #include <wchar.h>
           void error(char *function_name, wchar_t *format, ...)
           {
                 va_list args;
                    va_start(args, format);
                    // print out name of function causing error
                    fwprintf(stderr, L"ERROR in %s: ", function_name);
                    // print out remainder of message
                    vfwprintf(stderr, format, args);
                    va_end(args);
           }


7.29.2.6 [The vfwscanf function]


1          #include <stdarg.h>
           #include <stdio.h>
           #include <wchar.h>
           int vfwscanf(FILE * restrict stream,
                const wchar_t * restrict format,
                va_list arg);
    Description
2   The vfwscanf function is equivalent to fwscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfwscanf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vfwscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vfwscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.29.2.7 [The vswprintf function]


1           #include <stdarg.h>
            #include <wchar.h>
            int vswprintf(wchar_t * restrict s,
                 size_t n,
                 const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vswprintf function is equivalent to swprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vswprintf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vswprintf function returns the number of wide characters written in the array, not
    counting the terminating null wide character, or a negative value if an encoding error
    occurred or if n or more wide characters were requested to be generated.

7.29.2.8 [The vswscanf function]


1           #include <stdarg.h>
            #include <wchar.h>
            int vswscanf(const wchar_t * restrict s,
                 const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vswscanf function is equivalent to swscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vswscanf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vswscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vswscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.29.2.9 [The vwprintf function]


1          #include <stdarg.h>
           #include <wchar.h>
           int vwprintf(const wchar_t * restrict format,
                va_list arg);
    Description
2   The vwprintf function is equivalent to wprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vwprintf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vwprintf function returns the number of wide characters transmitted, or a negative
    value if an output or encoding error occurred.

7.29.2.10 [The vwscanf function]


1          #include <stdarg.h>
           #include <wchar.h>
           int vwscanf(const wchar_t * restrict format,
                va_list arg);
    Description
2   The vwscanf function is equivalent to wscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vwscanf function does not invoke the
    va_end macro.340)
    Returns
Footnote 340) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.
3   The vwscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vwscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.29.2.11 [The wprintf function]


1           #include <wchar.h>
            int wprintf(const wchar_t * restrict format, ...);
    Description
2   The wprintf function is equivalent to fwprintf with the argument stdout
    interposed before the arguments to wprintf.
    Returns
3   The wprintf function returns the number of wide characters transmitted, or a negative
    value if an output or encoding error occurred.

7.29.2.12 [The wscanf function]


1           #include <wchar.h>
            int wscanf(const wchar_t * restrict format, ...);
    Description
2   The wscanf function is equivalent to fwscanf with the argument stdin interposed
    before the arguments to wscanf.
    Returns
3   The wscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the wscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.

7.29.3 [Wide character input/output functions]

 Wide character input/output functions

7.29.3.1 [The fgetwc function]


1           #include <stdio.h>
            #include <wchar.h>
            wint_t fgetwc(FILE *stream);
    Description
2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
    next wide character is present, the fgetwc function obtains that wide character as a
    wchar_t converted to a wint_t and advances the associated file position indicator for
    the stream (if defined).
    Returns
3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
    of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
    the fgetwc function returns the next wide character from the input stream pointed to by
    stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
    function returns WEOF. If an encoding error occurs (including too few bytes), the value of
    the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.341)
Footnote 341) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
         Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.

7.29.3.2 [The fgetws function]


1           #include <stdio.h>
            #include <wchar.h>
            wchar_t *fgetws(wchar_t * restrict s,
                 int n, FILE * restrict stream);
    Description
2   The fgetws function reads at most one less than the number of wide characters
    specified by n from the stream pointed to by stream into the array pointed to by s. No
    additional wide characters are read after a new-line wide character (which is retained) or
    after end-of-file. A null wide character is written immediately after the last wide
    character read into the array.
    Returns
3   The fgetws function returns s if successful. If end-of-file is encountered and no
    characters have been read into the array, the contents of the array remain unchanged and a
    null pointer is returned. If a read or encoding error occurs during the operation, the array
    contents are indeterminate and a null pointer is returned.

7.29.3.3 [The fputwc function]


1           #include <stdio.h>
            #include <wchar.h>
            wint_t fputwc(wchar_t c, FILE *stream);
    Description
2   The fputwc function writes the wide character specified by c to the output stream
    pointed to by stream, at the position indicated by the associated file position indicator
    for the stream (if defined), and advances the indicator appropriately. If the file cannot

    support positioning requests, or if the stream was opened with append mode, the
    character is appended to the output stream.
    Returns
3   The fputwc function returns the wide character written. If a write error occurs, the
    error indicator for the stream is set and fputwc returns WEOF. If an encoding error
    occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.

7.29.3.4 [The fputws function]


1           #include <stdio.h>
            #include <wchar.h>
            int fputws(const wchar_t * restrict s,
                 FILE * restrict stream);
    Description
2   The fputws function writes the wide string pointed to by s to the stream pointed to by
    stream. The terminating null wide character is not written.
    Returns
3   The fputws function returns EOF if a write or encoding error occurs; otherwise, it
    returns a nonnegative value.

7.29.3.5 [The fwide function]


1           #include <stdio.h>
            #include <wchar.h>
            int fwide(FILE *stream, int mode);
    Description
2   The fwide function determines the orientation of the stream pointed to by stream. If
    mode is greater than zero, the function first attempts to make the stream wide oriented. If
    mode is less than zero, the function first attempts to make the stream byte oriented.342)
    Otherwise, mode is zero and the function does not alter the orientation of the stream.
    Returns
Footnote 342) If the orientation of the stream has already been determined, fwide does not change it.
3   The fwide function returns a value greater than zero if, after the call, the stream has
    wide orientation, a value less than zero if the stream has byte orientation, or zero if the
    stream has no orientation.


7.29.3.6 [The getwc function]


1          #include <stdio.h>
           #include <wchar.h>
           wint_t getwc(FILE *stream);
    Description
2   The getwc function is equivalent to fgetwc, except that if it is implemented as a
    macro, it may evaluate stream more than once, so the argument should never be an
    expression with side effects.
    Returns
3   The getwc function returns the next wide character from the input stream pointed to by
    stream, or WEOF.

7.29.3.7 [The getwchar function]


1          #include <wchar.h>
           wint_t getwchar(void);
    Description
2   The getwchar function is equivalent to getwc with the argument stdin.
    Returns
3   The getwchar function returns the next wide character from the input stream pointed to
    by stdin, or WEOF.

7.29.3.8 [The putwc function]


1          #include <stdio.h>
           #include <wchar.h>
           wint_t putwc(wchar_t c, FILE *stream);
    Description
2   The putwc function is equivalent to fputwc, except that if it is implemented as a
    macro, it may evaluate stream more than once, so that argument should never be an
    expression with side effects.
    Returns
3   The putwc function returns the wide character written, or WEOF.


7.29.3.9 [The putwchar function]


1           #include <wchar.h>
            wint_t putwchar(wchar_t c);
    Description
2   The putwchar function is equivalent to putwc with the second argument stdout.
    Returns
3   The putwchar function returns the character written, or WEOF.

7.29.3.10 [The ungetwc function]


1           #include <stdio.h>
            #include <wchar.h>
            wint_t ungetwc(wint_t c, FILE *stream);
    Description
2   The ungetwc function pushes the wide character specified by c back onto the input
    stream pointed to by stream. Pushed-back wide characters will be returned by
    subsequent reads on that stream in the reverse order of their pushing. A successful
    intervening call (with the stream pointed to by stream) to a file positioning function
    (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
    stream. The external storage corresponding to the stream is unchanged.
3   One wide character of pushback is guaranteed, even if the call to the ungetwc function
    follows just after a call to a formatted wide character input function fwscanf,
    vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
    on the same stream without an intervening read or file positioning operation on that
    stream, the operation may fail.
4   If the value of c equals that of the macro WEOF, the operation fails and the input stream is
    unchanged.
5   A successful call to the ungetwc function clears the end-of-file indicator for the stream.
    The value of the file position indicator for the stream after reading or discarding all
    pushed-back wide characters is the same as it was before the wide characters were pushed
    back. For a text or binary stream, the value of its file position indicator after a successful
    call to the ungetwc function is unspecified until all pushed-back wide characters are
    read or discarded.
    Returns
6   The ungetwc function returns the wide character pushed back, or WEOF if the operation
    fails.

7.29.4 [General wide string utilities]


1   The header <wchar.h> declares a number of functions useful for wide string
    manipulation. Various methods are used for determining the lengths of the arrays, but in
    all cases a wchar_t * argument points to the initial (lowest addressed) element of the
    array. If an array is accessed beyond the end of an object, the behavior is undefined.
2   Where an argument declared as size_t n determines the length of the array for a
    function, n can have the value zero on a call to that function. Unless explicitly stated
    otherwise in the description of a particular function in this subclause, pointer arguments
    on such a call shall still have valid values, as described in 7.1.4. On such a call, a
    function that locates a wide character finds no occurrence, a function that compares two
    wide character sequences returns zero, and a function that copies wide characters copies
    zero wide characters.

7.29.4.1 [Wide string numeric conversion functions]

 Wide string numeric conversion functions

7.29.4.1.1 [The wcstod, wcstof, and wcstold functions]


1          #include <wchar.h>
           double wcstod(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr);
           float wcstof(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr);
           long double wcstold(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr);
    Description
2   The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
    string pointed to by nptr to double, float, and long double representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space wide characters (as specified by the iswspace
    function), a subject sequence resembling a floating-point constant or representing an
    infinity or NaN; and a final wide string of one or more unrecognized wide characters,
    including the terminating null wide character of the input wide string. Then, they attempt
    to convert the subject sequence to a floating-point number, and return the result.
3   The expected form of the subject sequence is an optional plus or minus sign, then one of
    the following:
    -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
       character, then an optional exponent part as defined for the corresponding single-byte
       characters in 6.4.4.2;
    -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
       decimal-point wide character, then an optional binary exponent part as defined in
       6.4.4.2;
    -- INF or INFINITY, or any other wide string equivalent except for case
    -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
       case in the NAN part, where:
                 n-wchar-sequence:
                       digit
                       nondigit
                       n-wchar-sequence digit
                       n-wchar-sequence nondigit
    The subject sequence is defined as the longest initial subsequence of the input wide
    string, starting with the first non-white-space wide character, that is of the expected form.
    The subject sequence contains no wide characters if the input wide string is not of the
    expected form.
4   If the subject sequence has the expected form for a floating-point number, the sequence of
    wide characters starting with the first digit or the decimal-point wide character
    (whichever occurs first) is interpreted as a floating constant according to the rules of
     6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
    if neither an exponent part nor a decimal-point wide character appears in a decimal
    floating point number, or if a binary exponent part does not appear in a hexadecimal
    floating point number, an exponent part of the appropriate type with value zero is
    assumed to follow the last digit in the string. If the subject sequence begins with a minus
    sign, the sequence is interpreted as negated.343) A wide character sequence INF or
    INFINITY is interpreted as an infinity, if representable in the return type, else like a
    floating constant that is too large for the range of the return type. A wide character
    sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
    in the return type, else like a subject sequence part that does not have the expected form;
    the meaning of the n-wchar sequence is implementation-defined.344) A pointer to the

     final wide string is stored in the object pointed to by endptr, provided that endptr is
     not a null pointer.
Footnote 343) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
         negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
         methods may yield different results if rounding is toward positive or negative infinity. In either case,
         the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
Footnote 344) An implementation may use the n-wchar sequence to determine extra information to be represented in
         the NaN's significand.
5    If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
     value resulting from the conversion is correctly rounded.
6    In other than the "C" locale, additional locale-specific subject sequence forms may be
     accepted.
7    If the subject sequence is empty or does not have the expected form, no conversion is
     performed; the value of nptr is stored in the object pointed to by endptr, provided
     that endptr is not a null pointer.
     Recommended practice
8    If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
     the result is not exactly representable, the result should be one of the two numbers in the
     appropriate internal format that are adjacent to the hexadecimal floating source value,
     with the extra stipulation that the error should have a correct sign for the current rounding
     direction.
9    If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
     <float.h>) significant digits, the result should be correctly rounded. If the subject
     sequence D has the decimal form and more than DECIMAL_DIG significant digits,
     consider the two bounding, adjacent decimal strings L and U , both having
     DECIMAL_DIG significant digits, such that the values of L , D, and U satisfy L  D  U .
     The result should be one of the (equal or adjacent) values that would be obtained by
     correctly rounding L and U according to the current rounding direction, with the extra
     stipulation that the error with respect to D should have a correct sign for the current
     rounding direction.345)
     Returns
Footnote 345) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
          to the same internal floating value, but if not will round to adjacent values.
10   The functions return the converted value, if any. If no conversion could be performed,
     zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
     plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
     return type and sign of the value), and the value of the macro ERANGE is stored in
     errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
     no greater than the smallest normalized positive number in the return type; whether
     errno acquires the value ERANGE is implementation-defined.


7.29.4.1.2 [The wcstol, wcstoll, wcstoul, and wcstoull functions]


1           #include <wchar.h>
            long int wcstol(
                 const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr,
                 int base);
            long long int wcstoll(
                 const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr,
                 int base);
            unsigned long int wcstoul(
                 const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr,
                 int base);
            unsigned long long int wcstoull(
                 const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr,
                 int base);
    Description
2   The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
    portion of the wide string pointed to by nptr to long int, long long int,
    unsigned long int, and unsigned long long int representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space wide characters (as specified by the iswspace
    function), a subject sequence resembling an integer represented in some radix determined
    by the value of base, and a final wide string of one or more unrecognized wide
    characters, including the terminating null wide character of the input wide string. Then,
    they attempt to convert the subject sequence to an integer, and return the result.
3   If the value of base is zero, the expected form of the subject sequence is that of an
    integer constant as described for the corresponding single-byte characters in 6.4.4.1,
    optionally preceded by a plus or minus sign, but not including an integer suffix. If the
    value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
    is a sequence of letters and digits representing an integer with the radix specified by
    base, optionally preceded by a plus or minus sign, but not including an integer suffix.
    The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
    letters and digits whose ascribed values are less than that of base are permitted. If the
    value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
    of letters and digits, following the sign if present.

4   The subject sequence is defined as the longest initial subsequence of the input wide
    string, starting with the first non-white-space wide character, that is of the expected form.
    The subject sequence contains no wide characters if the input wide string is empty or
    consists entirely of white space, or if the first non-white-space wide character is other
    than a sign or a permissible letter or digit.
5   If the subject sequence has the expected form and the value of base is zero, the sequence
    of wide characters starting with the first digit is interpreted as an integer constant
    according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
    value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
    letter its value as given above. If the subject sequence begins with a minus sign, the value
    resulting from the conversion is negated (in the return type). A pointer to the final wide
    string is stored in the object pointed to by endptr, provided that endptr is not a null
    pointer.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Returns
8   The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
    value, if any. If no conversion could be performed, zero is returned. If the correct value
    is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
    LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
    sign of the value, if any), and the value of the macro ERANGE is stored in errno.

7.29.4.2 [Wide string copying functions]

 Wide string copying functions

7.29.4.2.1 [The wcscpy function]


1          #include <wchar.h>
           wchar_t *wcscpy(wchar_t * restrict s1,
                const wchar_t * restrict s2);
    Description
2   The wcscpy function copies the wide string pointed to by s2 (including the terminating
    null wide character) into the array pointed to by s1.
    Returns
3   The wcscpy function returns the value of s1.

7.29.4.2.2 [The wcsncpy function]


1            #include <wchar.h>
             wchar_t *wcsncpy(wchar_t * restrict s1,
                  const wchar_t * restrict s2,
                  size_t n);
    Description
2   The wcsncpy function copies not more than n wide characters (those that follow a null
    wide character are not copied) from the array pointed to by s2 to the array pointed to by
    s1.346)
Footnote 346) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
         result will not be null-terminated.
3   If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
    wide characters are appended to the copy in the array pointed to by s1, until n wide
    characters in all have been written.
    Returns
4   The wcsncpy function returns the value of s1.

7.29.4.2.3 [The wmemcpy function]


1            #include <wchar.h>
             wchar_t *wmemcpy(wchar_t * restrict s1,
                  const wchar_t * restrict s2,
                  size_t n);
    Description
2   The wmemcpy function copies n wide characters from the object pointed to by s2 to the
    object pointed to by s1.
    Returns
3   The wmemcpy function returns the value of s1.


7.29.4.2.4 [The wmemmove function]


1          #include <wchar.h>
           wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
                size_t n);
    Description
2   The wmemmove function copies n wide characters from the object pointed to by s2 to
    the object pointed to by s1. Copying takes place as if the n wide characters from the
    object pointed to by s2 are first copied into a temporary array of n wide characters that
    does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
    the temporary array are copied into the object pointed to by s1.
    Returns
3   The wmemmove function returns the value of s1.

7.29.4.3 [Wide string concatenation functions]

 Wide string concatenation functions

7.29.4.3.1 [The wcscat function]


1          #include <wchar.h>
           wchar_t *wcscat(wchar_t * restrict s1,
                const wchar_t * restrict s2);
    Description
2   The wcscat function appends a copy of the wide string pointed to by s2 (including the
    terminating null wide character) to the end of the wide string pointed to by s1. The initial
    wide character of s2 overwrites the null wide character at the end of s1.
    Returns
3   The wcscat function returns the value of s1.

7.29.4.3.2 [The wcsncat function]


1          #include <wchar.h>
           wchar_t *wcsncat(wchar_t * restrict s1,
                const wchar_t * restrict s2,
                size_t n);
    Description
2   The wcsncat function appends not more than n wide characters (a null wide character
    and those that follow it are not appended) from the array pointed to by s2 to the end of

    the wide string pointed to by s1. The initial wide character of s2 overwrites the null
    wide character at the end of s1. A terminating null wide character is always appended to
    the result.347)
    Returns
Footnote 347) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
         wcslen(s1)+n+1.
3   The wcsncat function returns the value of s1.

7.29.4.4 [Wide string comparison functions]


1   Unless explicitly stated otherwise, the functions described in this subclause order two
    wide characters the same way as two integers of the underlying integer type designated
    by wchar_t.

7.29.4.4.1 [The wcscmp function]


1           #include <wchar.h>
            int wcscmp(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcscmp function compares the wide string pointed to by s1 to the wide string
    pointed to by s2.
    Returns
3   The wcscmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
    wide string pointed to by s2.

7.29.4.4.2 [The wcscoll function]


1           #include <wchar.h>
            int wcscoll(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcscoll function compares the wide string pointed to by s1 to the wide string
    pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
    current locale.
    Returns
3   The wcscoll function returns an integer greater than, equal to, or less than zero,
    accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the

    wide string pointed to by s2 when both are interpreted as appropriate to the current
    locale.

7.29.4.4.3 [The wcsncmp function]


1          #include <wchar.h>
           int wcsncmp(const wchar_t *s1, const wchar_t *s2,
                size_t n);
    Description
2   The wcsncmp function compares not more than n wide characters (those that follow a
    null wide character are not compared) from the array pointed to by s1 to the array
    pointed to by s2.
    Returns
3   The wcsncmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
    to, or less than the possibly null-terminated array pointed to by s2.

7.29.4.4.4 [The wcsxfrm function]


1          #include <wchar.h>
           size_t wcsxfrm(wchar_t * restrict s1,
                const wchar_t * restrict s2,
                size_t n);
    Description
2   The wcsxfrm function transforms the wide string pointed to by s2 and places the
    resulting wide string into the array pointed to by s1. The transformation is such that if
    the wcscmp function is applied to two transformed wide strings, it returns a value greater
    than, equal to, or less than zero, corresponding to the result of the wcscoll function
    applied to the same two original wide strings. No more than n wide characters are placed
    into the resulting array pointed to by s1, including the terminating null wide character. If
    n is zero, s1 is permitted to be a null pointer.
    Returns
3   The wcsxfrm function returns the length of the transformed wide string (not including
    the terminating null wide character). If the value returned is n or greater, the contents of
    the array pointed to by s1 are indeterminate.
4   EXAMPLE The valu