C23

The next generation of the C standard.

See: The current IS schedule for C23.

Obsolete

Removed

• Old-style function declarations and definitions
• Representations for signed integers other than two's complement
• Permission that u/U-prefixed character constants and string literals may be not UTF-16/32
• Mixed wide string literal concatenation
• Support for calling realloc() with zero size (the behavior becomes undefined)
• __alignof_is_defined and __alignas_is_defined

Deprecated

• Old feature-test macros
  • __STDC_IEC_559__
  • __STDC_IEC_559_COMPLEX__
• _Noreturn function specifier
• _Noreturn attribute token
• asctime()
• ctime()
• DECIMAL_DIG
• Definition of following numeric limit macros in <math.h> (they should be used via <limits.h>)
  • INFINITY
  • DEC_INFINITY
  • NAN
  • DEC_NAN
• __bool_true_false_are_defined

New language features

• Decimal floating-point types (_Decimal32, _Decimal64, and _Decimal128)
• Bit-precise integers (_BitInt(N))
• Binary integer constants
• u8 character constants
• Type change of u8 string literals
• Digit separator '
• Empty initializer = {}
• Attributes
  • [[deprecated]]
  • [[fallthrough]]
  • [[maybe_unused]]
  • [[nodiscard]]
  • [[noreturn]]
• Unnamed parameters in function definitions
• Identical cvr-qualifications for array types and their element types
• Single-argument _Static_assert
• Labels followed by declarations and }
• nullptr constant and the associated nullptr_t type
• true and false become keywords (may be predefined macros for compatibility reasons)
• New preprocessor directives
  • #elifdef
  • #elifndef
  • #warning
  • #embed
• Pragmas for rounding direction
  • STDC FENV_ROUND
  • STDC FENV_DEC_ROUND

Feature test macros for optional features

• __STDC_IEC_60559_BFP__
  • Indicates IEEE-754 binary floating-point arithmetic and required math functions are supported.
  This macro supersedes __STDC_IEC_559__.
• __STDC_IEC_60559_DFP__
  • Indicates IEEE-754 decimal floating-point arithmetic and required math functions are supported.
• __STDC_IEC_60559_COMPLEX__
  • Indicates IEEE-754 complex arithmetic and required math functions are supported.
  This macro supersedes __STDC_IEC_559_COMPLEX__.

New library features

• Extended binary floating-point math functions
• Decimal floating-point math functions
  • -dN variants for existing and new floating-point math functions
  • quantizedN()
  • samequantumdN()
  • quantumdN()
  • llquantexpdN()
  • encodedecdN()
  • decodedecdN()
  • encodebindN()
  • decodebindN()
• Floating-point formatting functions
• Library support for UTF-8
  • char8_t type alias
  • mbrtoc8()
  • c8rtomb()
  • atomic_char8_t type alias
  • ATOMIC_CHAR8_T_LOCK_FREE test macro
• POSIX functions
  • memccpy()
  • strdup()
  • strndup()
  • gmtime_r()
  • localtime_r()
  • Extensions for strftime() and wcsftime()
• Extensions for fscanf() and fprintf() function families
  • wN and wfN length modifiers for [u]intN_t and [u]int_fastN_t respectively
  • H, D, and DD length modifiers for _Decimal32, _Decimal64, and _Decimal128 respectively
  • b conversion specifier for unsigned integer types
• timespec_getres()
• Macro constants for width of integer types
• Additional numeric limit macros for floating-point types
• Library version-test macros
  • __STDC_VERSION_FENV_H__
  • __STDC_VERSION_MATH_H__
  • __STDC_VERSION_STDINT_H__
  • __STDC_VERSION_STDLIB_H__
  • __STDC_VERSION_TGMATH_H__
  • __STDC_VERSION_TIME_H__

Defect reports

Compiler support

C23 core language features

C23 feature	Paper(s)	GCC	Clang	MSVC	Apple Clang	EDG eccp	Intel C++	IBM XLC++	Sun/Oracle C++	Embarcadero C++ Builder	Cray	Nvidia HPC C++ (ex Portland Group/PGI)	Nvidia nvcc
_Static_assert with no message	N2265	9	9		Yes
[[nodiscard]]	N2267	10	9		Yes
[[maybe_unused]]	N2270	10	9		Yes
[[deprecated]]	N2334	10	9		Yes
Attributes	N2335 N2554	10	9		Yes
IEEE 754 decimal floating-point types	N2341	4.2 (partial)*					13.0 (partial)*
[[fallthrough]]	N2408	10	9		Yes
u8 character constants	N2418	10	15
Removal of function definitions without prototype	N2432	10	15
[[nodiscard]] with message	N2448	11	10		Yes
Unnamed parameters in function definitions	N2480	11	11		Yes
Labels before declarations and end of blocks	N2508	11		Partial*			17.0*
Binary integer constants	N2549	4.3* 11	2.9* 9	19.0 (2015)**	Yes		11.0*
__has_c_attribute in preprocessor conditionals	N2553	11	9		Yes
Allow duplicate attributes	N2557	11	13		Yes
IEEE 754 interchange and extended types	N2601	7 (partial)*	6 (partial)*		Partial*
Digit separators	N2626	12	13	19.0 (2015)**	Yes		18.0*
#elifdef and #elifndef	N2645	12	13		13.1.6*
Type change of u8 string literals	N2653
[[maybe_unused]] for labels	N2662	11
#warning	N2686	Yes	Yes		Yes	Yes	Yes
Bit-precise integer types (_BitInt)	N2763		15
[[noreturn]]	N2764		15
Suffixes for bit-precise integer constants	N2775		15
__has_include in preprocessor conditionals	N2799	5	Yes	19.11*	Yes	4.13	18.0
Removal of function declarations without prototype	N2841		15
Empty initializers	N2900	Partial*	Partial*		Partial*	Partial*	Partial*
typeof and typeof_unqual	N2927	Partial*	Partial*		Partial*	Partial*	Partial*				Partial*
Predefined true and false	N2935
[[unsequenced]] and [[reproducible]]	N2956
Relax requirements for variadic parameter list	N2975
Type inference in object definitions	N3007
constexpr objects	N3008
nullptr	N3042
C23 feature	Paper(s)	GCC	Clang	MSVC	Apple Clang	EDG eccp	Intel C++	IBM XLC++	Sun/Oracle C++	Embarcadero C++ Builder	Cray	Nvidia HPC C++ (ex Portland Group/PGI)	Nvidia nvcc

C23 library features