choice of behavior in each of the areas that are designated
``implementation defined''. The following lists all such areas,
along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC
-9899:1999 and ISO/IEC 9899:2011 standards. Some areas are only
-implementation-defined in one version of the standard.
+9899:1999, ISO/IEC 9899:2011 and ISO/IEC 9899:2024 standards. Some
+areas are only implementation-defined in one version of the standard.
Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
@itemize @bullet
@item
-@cite{How a diagnostic is identified (C90 3.7, C99 and C11 3.10, C90,
-C99 and C11 5.1.1.3).}
+@cite{How a diagnostic is identified (C90 3.7, C99 and C11 3.10, C23
+3.13, C90, C99 and C11 5.1.1.3, C23 5.2.1.3).}
Diagnostics consist of all the output sent to stderr by GCC@.
@item
@cite{Whether each nonempty sequence of white-space characters other than
new-line is retained or replaced by one space character in translation
-phase 3 (C90, C99 and C11 5.1.1.2).}
+phase 3 (C90, C99 and C11 5.1.1.2, C23 5.2.1.2).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@item
@cite{The mapping between physical source file multibyte characters
and the source character set in translation phase 1 (C90, C99 and C11
-5.1.1.2).}
+5.1.1.2, C23 5.2.1.2).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@itemize @bullet
@item
@cite{Which additional multibyte characters may appear in identifiers
-and their correspondence to universal character names (C99 and C11 6.4.2).}
+and their correspondence to universal character names (C99 and C11
+6.4.2, C23 6.4.3).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@item
@cite{The number of significant initial characters in an identifier
-(C90 6.1.2, C90, C99 and C11 5.2.4.1, C99 and C11 6.4.2).}
+(C90 6.1.2, C90, C99 and C11 5.2.4.1, C23 5.3.5.2, C99 and C11 6.4.2,
+C23 6.4.3).}
For internal names, all characters are significant. For external names,
the number of significant characters are defined by the linker; for
@cite{Whether case distinctions are significant in an identifier with
external linkage (C90 6.1.2).}
-This is a property of the linker. C99 and C11 require that case distinctions
+This is a property of the linker. C99 and later require that case distinctions
are always significant in identifiers with external linkage and
systems without this property are not supported by GCC@.
@itemize @bullet
@item
-@cite{The number of bits in a byte (C90 3.4, C99 and C11 3.6).}
+@cite{The number of bits in a byte (C90 3.4, C99 and C11 3.6, C23 3.7).}
Determined by ABI@.
@item
@cite{The values of the members of the execution character set (C90,
-C99 and C11 5.2.1).}
+C99 and C11 5.2.1, C23 5.3.1).}
Determined by ABI@.
@item
@cite{The unique value of the member of the execution character set produced
for each of the standard alphabetic escape sequences (C90, C99 and C11
-5.2.2).}
+5.2.2, C23 5.3.3).}
Determined by ABI@.
@item
@cite{The value of a @code{char} object into which has been stored any
character other than a member of the basic execution character set
-(C90 6.1.2.5, C99 and C11 6.2.5).}
+(C90 6.1.2.5, C99, C11 and C23 6.2.5).}
Determined by ABI@.
@item
@cite{Which of @code{signed char} or @code{unsigned char} has the same
range, representation, and behavior as ``plain'' @code{char} (C90
-6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1).}
+6.1.2.5, C90 6.2.1.1, C99, C11 and C23 6.2.5, C99 and C11 6.3.1.1, C23
+6.3.2.1).}
@opindex fsigned-char
@opindex funsigned-char
@option{-fsigned-char} change the default. @xref{C Dialect Options, ,
Options Controlling C Dialect}.
+@item
+@cite{The literal encoding, which maps of the characters of the
+execution character set to the values in a character constant or
+string literal (C23 6.2.9, C23 6.4.5.5).}
+
+Determined by ABI@.
+
+@item
+@cite{The wide literal encoding, of the characters of the execution
+character set to the values in a @code{wchar_t} character constant or
+@code{wchar_t} string literal (C23 6.2.9, C23 6.4.5.5).}
+
+Determined by ABI@.
+
@item
@cite{The mapping of members of the source character set (in character
constants and string literals) to members of the execution character
-set (C90 6.1.3.4, C99 and C11 6.4.4.4, C90, C99 and C11 5.1.1.2).}
+set (C90 6.1.3.4, C99 and C11 6.4.4.4, C23 6.4.5.5, C90, C99 and C11
+5.1.1.2, C23 5.2.1.2).}
Determined by ABI@.
@item
@cite{The value of an integer character constant containing more than one
character or containing a character or escape sequence that does not map
-to a single-byte execution character (C90 6.1.3.4, C99 and C11 6.4.4.4).}
+to a single-byte execution character (C90 6.1.3.4, C99 and C11
+6.4.4.4, C23 6.4.5.5).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
multiple members of the extended execution character set, or
containing a multibyte character or escape sequence not represented in
the extended execution character set (C90 6.1.3.4, C99 and C11
-6.4.4.4).}
+6.4.4.4, C23 6.4.5.5).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@cite{The current locale used to convert a wide character constant consisting
of a single multibyte character that maps to a member of the extended
execution character set into a corresponding wide character code (C90
-6.1.3.4, C99 and C11 6.4.4.4).}
+6.1.3.4, C99 and C11 6.4.4.4, C23 6.4.5.5).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@item
@cite{The current locale used to convert a wide string literal into
-corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5).}
+corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5, C23 6.4.6).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@item
@cite{The value of a string literal containing a multibyte character or escape
sequence not represented in the execution character set (C90 6.1.4,
-C99 and C11 6.4.5).}
+C99 and C11 6.4.5, C23 6.4.6).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}.
@cite{The encoding of any of @code{wchar_t}, @code{char16_t}, and
@code{char32_t} where the corresponding standard encoding macro
(@code{__STDC_ISO_10646__}, @code{__STDC_UTF_16__}, or
-@code{__STDC_UTF_32__}) is not defined (C11 6.10.8.2).}
+@code{__STDC_UTF_32__}) is not defined (C11 6.10.8.2, C23 6.10.10.3).}
@xref{Implementation-defined behavior, , Implementation-defined
behavior, cpp, The C Preprocessor}. @code{char16_t} and
@itemize @bullet
@item
-@cite{Any extended integer types that exist in the implementation (C99
-and C11 6.2.5).}
+@cite{Any extended integer types that exist in the implementation (C99,
+C11 and C23 6.2.5).}
GCC does not support any extended integer types.
@c The __mode__ attribute might create types of precisions not
is a trap representation or an ordinary value (C99 and C11 6.2.6.2).}
GCC supports only two's complement integer types, and all bit patterns
-are ordinary values.
+are ordinary values. C23 requires signed integer types to be two's
+complement.
@item
@cite{The rank of any extended integer type relative to another extended
-integer type with the same precision (C99 and C11 6.3.1.1).}
+integer type with the same precision (C99 and C11 6.3.1.1, C23 6.3.2.1).}
GCC does not support any extended integer types.
@c If it did, there would only be one of each precision and signedness.
@item
@cite{The result of, or the signal raised by, converting an integer to a
signed integer type when the value cannot be represented in an object of
-that type (C90 6.2.1.2, C99 and C11 6.3.1.3).}
+that type (C90 6.2.1.2, C99 and C11 6.3.1.3, C23 6.3.2.3).}
For conversion to a type of width @math{N}, the value is reduced
modulo @math{2^N} to be within range of the type; no signal is raised.
@item
@cite{The results of some bitwise operations on signed integers (C90
-6.3, C99 and C11 6.5).}
+6.3, C99 and C11 6.5, C23 6.5.1).}
Bitwise operators act on the representation of the value including
both the sign and value bits, where the sign bit is considered
on negative numbers by sign extension.
As an extension to the C language, GCC does not use the latitude given in
-C99 and C11 only to treat certain aspects of signed @samp{<<} as undefined.
+C99 and later to treat certain aspects of signed @samp{<<} as undefined.
However, @option{-fsanitize=shift} (and @option{-fsanitize=undefined}) will
diagnose such cases. They are also diagnosed where constant
expressions are required.
@item
@cite{The sign of the remainder on integer division (C90 6.3.5).}
-GCC always follows the C99 and C11 requirement that the result of division is
+GCC always follows the C99 and later requirement that the result of division is
truncated towards zero.
@end itemize
@item
@cite{The accuracy of the floating-point operations and of the library
functions in @code{<math.h>} and @code{<complex.h>} that return floating-point
-results (C90, C99 and C11 5.2.4.2.2).}
+results (C90, C99 and C11 5.2.4.2.2, C23 5.3.5.3.3).}
The accuracy is unknown.
@item
@cite{The rounding behaviors characterized by non-standard values
of @code{FLT_ROUNDS}
-(C90, C99 and C11 5.2.4.2.2).}
+(C90, C99 and C11 5.2.4.2.2, C23 5.3.5.3.3).}
+
+GCC does not use such values.
+
+@item
+@cite{The evaluation methods characterized by non-standard negative
+values of @code{FLT_EVAL_METHOD} (C99 and C11 5.2.4.2.2, C23 5.3.5.3.3).}
GCC does not use such values.
@item
@cite{The evaluation methods characterized by non-standard negative
-values of @code{FLT_EVAL_METHOD} (C99 and C11 5.2.4.2.2).}
+values of @code{DEC_EVAL_METHOD} (C23 5.3.5.3.4).}
GCC does not use such values.
+@item
+@cite{If decimal floating types are supported (C23 6.2.5).}
+
+These are supported for certain AArch64, i386, x86-64, PowerPC and
+S/390 targets only.
+
@item
@cite{The direction of rounding when an integer is converted to a
floating-point number that cannot exactly represent the original
-value (C90 6.2.1.3, C99 and C11 6.3.1.4).}
+value (C90 6.2.1.3, C99 and C11 6.3.1.4, C23 6.3.2.4).}
C99 Annex F is followed.
@item
@cite{The direction of rounding when a floating-point number is
converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11
-6.3.1.5).}
+6.3.1.5, C23 6.3.2.5).}
C99 Annex F is followed.
@cite{How the nearest representable value or the larger or smaller
representable value immediately adjacent to the nearest representable
value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11
-6.4.4.2).}
+6.4.4.2, C23 6.4.5.3).}
C99 Annex F is followed.
@item
@cite{Whether and how floating expressions are contracted when not
-disallowed by the @code{FP_CONTRACT} pragma (C99 and C11 6.5).}
+disallowed by the @code{FP_CONTRACT} pragma (C99 and C11 6.5, C23
+6.5.1).}
Expressions are currently only contracted if @option{-ffp-contract=fast},
@option{-funsafe-math-optimizations} or @option{-ffast-math} are used.
@item
@cite{The default state for the @code{FENV_ACCESS} pragma (C99 and C11
-7.6.1).}
+7.6.1, C23 7.6.2).}
This pragma is not implemented, but the default is to ``off'' unless
@option{-frounding-math} is used and @option{-fno-trapping-math} is not
@item
@cite{Additional floating-point exceptions, rounding modes, environments,
-and classifications, and their macro names (C99 and C11 7.6, C99 and
-C11 7.12).}
+and classifications, and their macro names (C99, C11 and C23 7.6, C99,
+C11 and C23 7.12).}
This is dependent on the implementation of the C library, and is not
defined by GCC itself.
@item
@cite{The default state for the @code{FP_CONTRACT} pragma (C99 and C11
-7.12.2).}
+7.12.2, C23 7.12.3).}
This pragma is not implemented. Expressions are currently only
contracted if @option{-ffp-contract=fast},
@end itemize
+@node Constant expressions implementation
+@section Constant expressions
+
+@itemize @bullet
+@item
+@cite{Whether or not an expression not explicitly sanctioned by this
+document is an extended constant expression, whether or not such
+extended constant expressions can be used in the same contexts as this
+document, and whether or not such extended constant expressions can
+affect potentially detectable semantic changes in the program (C23
+6.6).}
+
+The only extended constant expressions are those using other GNU
+extensions to the C language. Such extended constant expressions
+include integer constant expressions and arithmetic constant
+expressions.
+
+@end itemize
+
@node Arrays and pointers implementation
@section Arrays and Pointers
@itemize @bullet
@item
@cite{The result of converting a pointer to an integer or
-vice versa (C90 6.3.4, C99 and C11 6.3.2.3).}
+vice versa (C90 6.3.4, C99 and C11 6.3.2.3, C23 6.3.3.3).}
A cast from pointer to integer discards most-significant bits if the
pointer representation is larger than the integer type,
@item
@cite{The size of the result of subtracting two pointers to elements
-of the same array (C90 6.3.6, C99 and C11 6.5.6).}
+of the same array (C90 6.3.6, C99 and C11 6.5.6, C23 6.5.7).}
The value is as specified in the standard and the type is determined
by the ABI@.
@itemize @bullet
@item
@cite{The extent to which suggestions made by using the @code{register}
-storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).}
+storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1,
+C23 6.7.2).}
The @code{register} specifier affects code generation only in these ways:
@item
@cite{The extent to which suggestions made by using the inline function
-specifier are effective (C99 and C11 6.7.4).}
+specifier are effective (C99 and C11 6.7.4, C23 6.7.5).}
GCC will not inline any functions if the @option{-fno-inline} option is
used or if @option{-O0} is used. Otherwise, GCC may still be unable to
@item
@cite{Whether a ``plain'' @code{int} bit-field is treated as a
@code{signed int} bit-field or as an @code{unsigned int} bit-field
-(C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).}
+(C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C23 6.7.3, C99 and C11
+6.7.2.1, C23 6.7.3.2).}
@opindex funsigned-bitfields
By default it is treated as @code{signed int} but this may be changed
@item
@cite{Allowable bit-field types other than @code{_Bool}, @code{signed int},
-and @code{unsigned int} (C99 and C11 6.7.2.1).}
+and @code{unsigned int} (C99 and C11 6.7.2.1, C23 6.7.3.2).}
Other integer types, such as @code{long int}, and enumerated types are
permitted even in strictly conforming mode.
@item
-@cite{Whether atomic types are permitted for bit-fields (C11 6.7.2.1).}
+@cite{Whether atomic types are permitted for bit-fields (C11 6.7.2.1,
+C23 6.7.3.2).}
Atomic types are not permitted for bit-fields.
@item
@cite{Whether a bit-field can straddle a storage-unit boundary (C90
-6.5.2.1, C99 and C11 6.7.2.1).}
+6.5.2.1, C99 and C11 6.7.2.1, C23 6.7.3.2).}
Determined by ABI@.
@item
@cite{The order of allocation of bit-fields within a unit (C90
-6.5.2.1, C99 and C11 6.7.2.1).}
+6.5.2.1, C99 and C11 6.7.2.1, C23 6.7.3.2).}
Determined by ABI@.
@item
@cite{The alignment of non-bit-field members of structures (C90
-6.5.2.1, C99 and C11 6.7.2.1).}
+6.5.2.1, C99 and C11 6.7.2.1, C23 6.7.3.2).}
Determined by ABI@.
@item
@cite{The integer type compatible with each enumerated type (C90
-6.5.2.2, C99 and C11 6.7.2.2).}
+6.5.2.2, C99 and C11 6.7.2.2, C23 6.7.3.3).}
@opindex fshort-enums
Normally, the type is @code{unsigned int} if there are no negative
@itemize @bullet
@item
@cite{What constitutes an access to an object that has volatile-qualified
-type (C90 6.5.3, C99 and C11 6.7.3).}
+type (C90 6.5.3, C99 and C11 6.7.3, C23 6.7.4).}
Such an object is normally accessed by pointers and used for accessing
hardware. In most expressions, it is intuitively obvious what is a read
@end itemize
+@node Types implementation
+@section Types
+
+@itemize @bullet
+@item
+@cite{A program forms the composite type of an enumerated type and a
+non-enumeration integer type (C23 6.2.7).}
+
+The composite type is the enumerated type.
+
+@item
+@cite{Whether or not it is supported for a declaration for which a
+type is inferred to contain a pointer, array, or function declarator
+(C23 6.7.10).}
+
+This is not supported.
+
+@item
+@cite{Whether or not it is supported for a declaration for which a
+type is inferred to contain no or more than one declarators (C23
+6.7.10).}
+
+This is not supported.
+
+@end itemize
+
@node Declarators implementation
@section Declarators
@itemize @bullet
@item
@cite{The locations within @code{#pragma} directives where header name
-preprocessing tokens are recognized (C11 6.4, C11 6.4.7).}
+preprocessing tokens are recognized (C11 and C23 6.4, C11 6.4.7, C23
+6.4.8).}
@item
@cite{How sequences in both forms of header names are mapped to headers
-or external source file names (C90 6.1.7, C99 and C11 6.4.7).}
+or external source file names (C90 6.1.7, C99 and C11 6.4.7, C23
+6.4.8).}
@item
@cite{Whether the value of a character constant in a constant expression
that controls conditional inclusion matches the value of the same character
-constant in the execution character set (C90 6.8.1, C99 and C11 6.10.1).}
+constant in the execution character set (C90 6.8.1, C99 and C11
+6.10.1, C23 6.10.2).}
@item
@cite{Whether the value of a single-character character constant in a
constant expression that controls conditional inclusion may have a
-negative value (C90 6.8.1, C99 and C11 6.10.1).}
+negative value (C90 6.8.1, C99 and C11 6.10.1, C23 6.10.2).}
@item
@cite{The places that are searched for an included @samp{<>} delimited
header, and how the places are specified or the header is
-identified (C90 6.8.2, C99 and C11 6.10.2).}
+identified (C90 6.8.2, C99 and C11 6.10.2, C23 6.10.3).}
@item
@cite{How the named source file is searched for in an included @samp{""}
-delimited header (C90 6.8.2, C99 and C11 6.10.2).}
+delimited header (C90 6.8.2, C99 and C11 6.10.2, C23 6.10.3).}
+
+@item
+@cite{How the named resource file is searched for in an embedded @samp{""}
+delimited resource name (C23 6.10.4).}
@item
@cite{The method by which preprocessing tokens (possibly resulting from
macro expansion) in a @code{#include} directive are combined into a header
-name (C90 6.8.2, C99 and C11 6.10.2).}
+name (C90 6.8.2, C99 and C11 6.10.2, C23 6.10.3).}
@item
@cite{The nesting limit for @code{#include} processing (C90 6.8.2, C99
-and C11 6.10.2).}
+and C11 6.10.2, C23 6.10.3).}
+
+@item
+@cite{The method by which preprocessing tokens (possibly resulting
+from macro expansion) in a @code{#embed} directive are combined into a
+resource name (C23 6.10.4).}
+
+@item
+@cite{The mapping between a resource's data and the values of the
+integer constant expressions, if any, in the replacement of a
+@code{#embed} directive (C23 6.10.4).}
+
+@item
+@cite{The width of a resource located by the @code{#embed} directive
+(C23 6.10.4).}
@item
@cite{Whether the @samp{#} operator inserts a @samp{\} character before
the @samp{\} character that begins a universal character name in a
-character constant or string literal (C99 and C11 6.10.3.2).}
+character constant or string literal (C99 and C11 6.10.3.2, C23
+6.10.5.3).}
@item
@cite{The behavior on each recognized non-@code{STDC #pragma}
-directive (C90 6.8.6, C99 and C11 6.10.6).}
+directive (C90 6.8.6, C99 and C11 6.10.6, C23 6.10.8).}
@xref{Pragmas, , Pragmas, cpp, The C Preprocessor}, for details of
pragmas accepted by GCC on all targets. @xref{Pragmas, , Pragmas
@item
@cite{The definitions for @code{__DATE__} and @code{__TIME__} when
respectively, the date and time of translation are not available (C90
-6.8.8, C99 6.10.8, C11 6.10.8.1).}
+6.8.8, C99 6.10.8, C11 6.10.8.1, C23 6.10.10.2).}
@end itemize
@itemize @bullet
@item
@cite{The null pointer constant to which the macro @code{NULL} expands
-(C90 7.1.6, C99 7.17, C11 7.19).}
+(C90 7.1.6, C99 7.17, C11 7.19, C23 7.21).}
In @code{<stddef.h>}, @code{NULL} expands to @code{((void *)0)}. GCC
does not provide the other headers which define @code{NULL} and some
@item
@cite{The values or expressions assigned to the macros specified in the
headers @code{<float.h>}, @code{<limits.h>}, and @code{<stdint.h>}
-(C90, C99 and C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11 7.20.2, C11 7.20.3).}
+(C90, C99 and C11 5.2.4.2, C23 5.3.5.3, C99 7.18.2, C99 7.18.3, C11
+7.20.2, C11 7.20.3, C23 7.22).}
Determined by ABI@.
@item
@cite{The result of attempting to indirectly access an object with
automatic or thread storage duration from a thread other than the one
-with which it is associated (C11 6.2.4).}
+with which it is associated (C11 and C23 6.2.4).}
Such accesses are supported, subject to the same requirements for
synchronization for concurrent accesses as for concurrent accesses to
@item
@cite{The number, order, and encoding of bytes in any object
-(when not explicitly specified in this International Standard) (C99
-and C11 6.2.6.1).}
+(when not explicitly specified in this International Standard) (C99,
+C11 and C23 6.2.6.1).}
Determined by ABI@.
@item
@cite{Whether any extended alignments are supported and the contexts
-in which they are supported (C11 6.2.8).}
+in which they are supported (C11 and C23 6.2.8).}
Extended alignments up to @math{2^{28}} (bytes) are supported for
objects of automatic storage duration. Alignments supported for
@item
@cite{Valid alignment values other than those returned by an _Alignof
-expression for fundamental types, if any (C11 6.2.8).}
+expression for fundamental types, if any (C11 and C23 6.2.8).}
Valid alignments are powers of 2 up to and including @math{2^{28}}.
@item
@cite{The value of the result of the @code{sizeof} and @code{_Alignof}
-operators (C90 6.3.3.4, C99 and C11 6.5.3.4).}
+operators (C90 6.3.3.4, C99 and C11 6.5.3.4, C23 6.5.4.5).}
Determined by ABI@.
projects / thirdparty / gcc.git / commitdiff
