# C99

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

| This section is incomplete Reason: core/library features, TC1~TC3, DRs

## 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()
  - imaxabs()
  - lldiv()
  - imaxdiv()
- 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`)

## Defect reports

Template:c/language/history/DR99

## Compiler support

### C99 core language features

| This section is incomplete Reason: needs to list C compilers, verification

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

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