The standalone C library functions

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2.4.5. The standalone C library functions

The rest of this section lists the include files, and the functions they contain, that are available with an uninitialized library. Some otherwise‑unavailable functions can be used if the library functions they depend on are re‑implemented.

alloca.h

Functions listed in this file are not available without library initialization. See Building an application with the C library for instructions.

assert.h

Functions listed in this file require high‑level stdio, __rt_raise(), and _sys_exit(). See Tailoring error signaling, error handling, and program exit for instructions.

ctype.h

Functions listed in this file require the locale functions.

errno.h

Functions in this file work without the requirement for any library initialization or function re‑implementation.

fenv.h

Functions in this file work without the requirement for any library initialization and only require the re‑implementation of __rt_raise().

float.h

This file does not contain any code. The definitions in the file do not require library initialization or function re‑implementation.

inttypes.h

Functions listed in this file require the locale functions.

limits.h

Functions in this file work without the requirement for any library initialization or function re‑implementation.

locale.h

Call setlocale() before calling any function that uses locale functions. For example:

setlocale(LC_ALL, "C")

See the contents of locale.h for more information on the following functions and data structures:

setlocale() selects the appropriate locale as specified by the category and locale arguments
lconv is the structure used by locale functions for formatting numeric quantities according to the rules of the current locale.
localeconv() creates an lconv structure and returns a pointer to it
_get_lconv() fills the lconv structure pointed to by the parameter. This ISO extension removes the requirement for static data within the library.

locale.h also contains constant declarations used with locale functions. See Tailoring locale and CTYPE using assembler macros for more information.

math.h

For functions in this file to work, you must first call _fp_init() and re‑implement __rt_raise().

setjmp.h

Functions in this file work without any library initialization or function re‑implementation.

signal.h

Functions listed in this file are not available without library initialization. See Building an application with the C library for instructions on building an application that uses library initialization.

__rt_raise() can be re‑implemented for error and exit handling. See Tailoring error signaling, error handling, and program exit for instructions.

stdarg.h

Functions listed in this file work without any library initialization or function re‑implementation.

stddef.h

This file does not contain any code. The definitions in the file do not require library initialization or function re‑implementation.

stdint.h

This file does not contain any code. The definitions in the file do not require library initialization or function re‑implementation.

stdio.h

The following dependencies or limitations apply to these functions:

The high‑level functions such as printf(), scanf(), puts(), fgets(), fread(), fwrite(), and perror() depend on lower‑level stdio functions fgetc(), fputc(), and __backspace(). You must re‑implement these lower‑level functions when using the standalone C library.
However, you cannot re‑implement the _sys_ prefixed functions (for example, _sys_read()) when using the standalone C library because they require library initialization.
See Tailoring the input/output functions for more information.
The printf() and scanf() family of functions require locale.
The remove() and rename() functions are system‑specific and probably not usable in your application.

stdlib.h

Most functions in this file work without any library initialization or function re‑implementation. The following functions depend on other functions being instantiated correctly:

ato*() requires locale
strto*() requires locale
malloc(), calloc(), realloc(), and free() require heap functions
atexit() is not available when building an application without the C library.

string.h

Functions in this file work without any library initialization, with the exception of strcoll() and strxfrm(), that require locale.

time.h

mktime() and localtime() can be used immediately
time() and clock() are system‑specific and probably not usable unless re‑implemented
asctime(), ctime(), and strftime() require locale.

wchar.h

Wide character library functions added to ISO C by Normative Addendum 1 in 1994.

Support for wide‑character output and format strings, swprintf(), vswprintf(), swscanf(), and vswscanf()
All the conversion functions (for example, btowc, wctob, mbrtowc, and wcrtomb) require locale
wcscoll and wcsxfrm require locale.

wctype.h

Wide character library functions added to ISO C by Normative Addendum 1 in 1994. This requires locale.

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