Standard library reference

Headers

ANSI C (C89)/ISO C (C90)

`assert.h`	Verify program assertion file
`ctype.h`	Character types file.
`errno.h`	System error numbers file
`float.h`	Floating types file
`limits.h`	Implementation-defined constants file.
`locale.h`	Category macros file.
`math.h`	Mathematical declarations file.
`setjmp.h`	Stack environment declarations file.
`signal.h`	Signals file.
`stdarg.h`	Handle variable argument list file.
`stddef.h`	Standard type definitions file.
`stdio.h`	Standard buffered input/output file.
`stdlib.h`	Standard library definitions file.
`string.h`	String operations file.
`time.h`	Time types file.

ISO C (C94/C95), Amendment 1 (AMD1)

Very old compilers may not include some or all of these headers

`iso646.h`	Alternative spellings.
`wchar.h`	Wide-character handling.
`wctype.h`	Wide-character classification and mapping utilities.

ISO C (C99)

These are supported only in newer compilers

`complex.h`	Complex arithmetic.
`fenv.h`	Floating-point environment.
`inttypes.h`	Fixed size integer types.
`stdbool.h`	Boolean type and values.
`stdint.h`	Integer types.
`tgmath.h`	Type-generic macros.

ISO C (C11)

These are supported only in newer compilers

`stdalign.h`	Alignment keywords and macros.
`stdatomic.h`	Atomic operations on data shared between threads.
`stdnoreturn.h`	_Noreturn function specifier macro.
`threads.h`	Support for multiple threads of execution.
`uchar.h`	Types and functions for manipulating Unicode characters.

Table of functions

This table also includes function-like macros

assert.h

assert

complex.h

- `cacos` - `cacosf` - `cacosl` - `casin` - `casinf` - `casinl` - `catan` - `catanf`	- `catanl` - `ccos` - `ccosf` - `ccosl` - `csin` - `csinf` - `csinl` - `ctan`	- `ctanf` - `ctanl` - `cacosh` - `cacoshf` - `cacoshl` - `casinh` - `casinhf` - `casinhl`	- `catanh` - `catanhf` - `catanhl` - `ccosh` - `ccoshf` - `ccoshl` - `csinh` - `csinhf`	- `csinhl` - `ctanh` - `ctanhf` - `ctanhl` - `cexp` - `cexpf` - `cexpl` - `clog`	- `clogf` - `clogl` - `cabs` - `cabsf` - `cabsl` - `cpow` - `cpowf` - `cpowl`	- `csqrt` - `csqrtf` - `csqrtl` - `carg` - `cargf` - `cargl` - `cimag` - `cimagf`	- `cimagl` - `conj` - `conjf` - `conjl` - `cproj` - `cprojf` - `cprojl` - `creal`	- `crealf` - `creall`

ctype.h

- `isalnum` - `isalpha` - `isblank` - `iscntrl`	- `isdigit` - `isgraph` - `islower` - `isprint`	- `ispunct` - `isspace` - `isupper` - `isxdigit`	- `tolower` - `toupper`

fenv.h

- `feclearexcept` - `fegetenv` - `fegetexceptflag` - `fegetround`	- `feholdexcept` - `feraiseexcept` - `fesetenv` - `fesetexceptflag`	- `fesetround` - `fetestexcept` - `feupdateenv`

inttypes.h

imaxabs
imaxdiv
strtoimax
strtoumax
wcstoimax
wcstoumax

locale.h

localeconv
setlocale

math.h

- `fpclassify` - `isfinite` - `isgreater` - `isgreaterequal`	- `isinf` - `isless` - `islessequal` - `islessgreater`	- `isnan` - `isnormal` - `isunordered` - `signbit`

setjmp.h

longjmp
setjmp

signal.h

raise

stdarg.h

va_arg
va_copy
va_end
va_start

stdatomic.h

- `atomic_init` - `atomic_thread_fence` - `atomic_signal_fence` - `atomic_is_lock_free` - `atomic_store` - `atomic_store_explicit` - `atomic_load` - `atomic_load_explicit`	- `atomic_exchange` - `atomic_exchange_explicit` - `atomic_compare_exchange_strong` - `atomic_compare_exchange_strong_explicit` - `atomic_compare_exchange_weak` - `atomic_compare_exchange_weak_explicit` - `atomic_fetch` - `atomic_fetch_key_explicit`	- `atomic_flag_test_and_set` - `atomic_flag_test_and_set_explicit` - `atomic_flag_clear` - `atomic_flag_clear_explicit`

stddef.h

offsetof

stdio.h

- `clearerr` - `fclose` - `feof` - `fgetc` - `fgetpos` - `fgets` - `fopen` - `fprintf` - `fputs`	- `fread` - `fscanf` - `fseek` - `fsetpos` - `ftell` - `fwprintf` - `fwrite` - `getc` - `getchar`	- `gets` - `perror` - `printf` - `putc` - `putchar` - `puts` - `remove` - `rename` - `rewind`	- `scanf` - `setbuf` - `setvbuf` - `sprintf` - `tmpfile` - `ungetc` - `vwprintf` - `wprintf` - `wscanf`

stdlib.h

- `abort` - `abs` - `labs` - `atexit`	- `atof` - `atoi` - `atol` - `bsearch`	- `div` - `ldiv` - `exit` - `free`	- `getenv` - `malloc` - `calloc` - `realloc`	- `qsort` - `rand` - `srand` - `strtod`	- `strtol` - `strtoul` - `system`

string.h

- `memchr` - `memcmp` - `memcpy` - `memmove` - `mempcpy`	- `memset` - `strcat` - `strncat` - `strchr`	- `strcmp` - `strncmp` - `strcoll` - `strcpy`	- `strncpy` - `strcspn` - `strerror` - `strlen`	- `strpbrk` - `strrchr` - `strspn` - `strstr`	- `strtok` - `strxfrm`

threads.h

- `call_once` - `cnd_broadcast` - `cnd_destroy` - `cnd_init` - `cnd_signal` - `cnd_timedwait` - `cnd_wait` - `mtx_destroy`	- `mtx_init` - `mtx_lock` - `mtx_timedlock` - `mtx_trylock` - `mtx_unlock` - `thrd_create` - `thrd_current` - `thrd_detach`	- `thrd_equal` - `thrd_exit` - `thrd_join` - `thrd_sleep` - `thrd_yield` - `tss_create` - `tss_delete` - `tss_get`	- `tss_set`

time.h

- `asctime` - `clock` - `ctime` - `difftime`	- `gmtime` - `localtime` - `mktime` - `strftime`	- `time`

uchar.h

mbrtoc16
c16rtomb
mbrtoc32
c32rtomb

wchar.h

- `btowc` - `fgetwc` - `fgetws` - `fputwc` - `fwide` - `fwprintf` - `fwscanf` - `getwc`	- `getwchar` - `mbrlen` - `mbrtowc` - `mbsinit` - `mbsrtowcs` - `putwc` - `putwchar` - `swprintf`	- `swscanf` - `ungetwc` - `vfwprintf` - `vswprintf` - `vwprintf` - `wcrtomb` - `wcscat` - `wcschr`	- `wcscmp` - `wcscoll` - `wcscpy` - `wcscspn` - `wcsftime` - `wcslen` - `wcsncat` - `wcsncmp`	- `wcsncpy` - `wcspbrk` - `wcsrchr` - `wcsrtombs` - `wcsspn` - `wcsstr` - `wcstod` - `wcstok`	- `wcstol` - `wcstoul` - `wcsxfrm` - `wctob` - `wmemchr` - `wmemcmp` - `wmemcpy` - `wmemmove`	- `wmemset` - `wprintf` - `wscanf`

wctype.h

- `iswalnum` - `iswalpha` - `iswcntrl` - `iswctype`	- `iswdigit` - `iswgraph` - `iswlower` - `iswprint`	- `iswpunct` - `iswspace` - `iswupper` - `iswxdigit`	- `towctrans` - `towlower` - `towupper` - `wctrans`	- `wctype`

Source: Wikibooks – Standard library reference. Licensed under CC BY-SA 3.0.