C99

 

C

Compiler support

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

Versions

C89

C95

C99

C11

C17

C23

Current status

 

ISO/IEC 9899:1999, a.k.a. C99, is a previous revision of the C standard.

Obsolete

Removed

• Implicit int in declarations
• Implicit function declarations

Deprecated

• gets()

New language features

• Universal-character-names in identifiers
• Increased translation limits
• // comments
• restrict pointers
• Enhanced arithmetic types
  • _Bool
  • long long and unsigned long long
  • Extended integer types
  • _Complex types (float _Complex, double _Complex, and long double _Complex)
  • _Imaginary types (float _Imaginary, double _Imaginary, and long double _Imaginary)
• Flexible array members
• Variable-length array (VLA) types and variably-modified (VM) types
• Improvements of braced-init-list for array, struct and union types
  • Non-constant initializers
  • Designated initializers
• Idempotent cvr-qualifiers
• Trailing comma in enumerator-list
• Hexadecimal floating constants
• Compound literals
• Floating-point environment
• Requiring truncation for divisions of signed integer types
• Implicit return 0; in the main() function
• Declarations and statements in mixed order
• init-statement in for loops
• inline functions
• Predefined variable __func__
• Cvr-qualifiers and static in [] within function declarations
• Variadic macros
• _Pragma preprocessor operator
• Standard pragmas for floating-point evaluation
  • STDC FENV_ACCESS
  • STDC FP_CONTRACT
  • STDC CX_LIMITED_RANGE

Feature test macros for optional features

• __STDC_IEC_559__
  • Indicates IEEE-754 binary floating-point arithmetic and required math functions are supported.
• __STDC_IEC_559_COMPLEX__
  • Indicates IEEE-754 complex arithmetic and required math functions are supported.
• __STDC_HOSTED__
  • Indicates that the implementation is hosted.
• __STDC_ISO_10646__
  • Indicates that Unicode is used by the wide literal encodings and expands to the latest supported revision.
• __STDC_MB_MIGHT_NEQ_WC__
  • Indicates that there are some characters in the basic character set having different code unit values in ordinary and wide literal encodings.

New library features

New headers

• <complex.h>
• <fenv.h>
• <inttypes.h>
• <stdbool.h>
• <stdint.h>
• <tgmath.h>

Library features

• Aliases for integer types
  • Integer types with exact width (intN_t and uintN_t)
  • Fastest integer types with at least given width (int_fastN_t and uint_fastN_t)
  • Smallest integer types with at least given width (int_leastN_t and uint_leastN_t)
  • Integer types capable for cast between object pointers (intptr_t and uintptr_t)
  • Integer types with maximum width (intmax_t and uintmax_t)
• Operations on long long and intmax_t
  • llabs()
  • abs
  • div
  • div
• Floating-point environment access
• Extended floating-point math functions
  • New floating-point math functions
  • -f and -l variants for existing and new floating-point math functions
  • Math error handling
• Complex functions
• _Exit()
• Formatting support for long long, unsigned long long, intmax_t, and uintmax_t
  • atoll()
  • strtoimax()
  • strtoll()
  • strtoull
  • strtoumax()
  • wcstoimax()
  • wcstoll()
  • wcstoull()
  • wcstoumax()
• isblank() and iswblank()
• snprintf() and vsnprintf()
• vfscanf() and vfwscanf() function families
• Extensions for fscanf() and fprintf() function families
  • ll length modifier for long long and unsigned long long
  • hh length modifier for signed char and unsigned char
  • l length modifier for double
  • z length modifier for size_t and its signed version
  • t length modifier for ptrdiff_t and its unsigned version
  • j length modifier for intmax_t and uintmax_t
  • a conversion specifier for floating-point types
• Numeric limit macros for long long and unsigned long long
• Numeric limit macros corresponding to existing and new aliases for integer types
• Format string macros for integer types
• va_copy
• Type-generic math macros
• Floating-point comparison macros
• Floating-point classification macros
• Compatibility macros for _Bool (bool, true, and false)

Compiler support

C99 core language features

C99 feature	Paper(s)	GCC	Clang	MSVC	Apple Clang	EDG eccp	Intel C++	Nvidia HPC C++ (ex PGI)*	Nvidia nvcc	Cray
Universal-character-names in identifiers		3.1	Yes	Yes
Increased translation limits	N590	0.9	N/A
// comments	N644	2.7	Yes	Yes
restrict pointers	N448	2.95	Yes	partial*
Enhanced arithmetic types	N815 N601 N620 N638 N657 N694 N809	Yes	partial	Maybe
Flexible array members		3.0	Yes	Yes
Variable-length array (VLA) types	N683	0.9	Yes
Variably-modified (VM) types	N2778	N/A	Yes
Designated initializers	N494	3.0	Yes	Yes
Non-constant initializers		1.21	N/A
Idempotent cvr-qualifiers	N505	3.0	N/A
Trailing comma in enumerator-list		0.9	Yes	Yes
Hexadecimal floating constants	N308	2.8	Yes	Yes
Compound literals	N716	3.1	Yes	Yes
Floating-point environment		partial	partial
Requiring truncation for divisions of signed integer types	N617	0.9	N/A
Implicit return 0; in the main() function		Yes	Yes	Yes
Declarations and statements in mixed order	N740	3.0	Yes	Yes
init-statement in for loops		Yes	Yes	Yes
inline functions	N741	4.3	Yes	Yes
Predefined variable __func__	N611	2.95	Yes	Yes
Cvr-qualifiers and static in [] within function declarations		3.1	Yes
Variadic macros	N707	2.95	Yes	Yes
_Pragma preprocessor operator	N634	3.0	Yes	partial*
Standard pragmas for floating-point evaluation	N631 N696	No	No
C99 feature	Paper(s)	GCC	Clang	MSVC	Apple Clang	EDG eccp	Intel C++	Nvidia HPC C++ (ex PGI)*	Nvidia nvcc	Cray