Building an application without the C library

ARM Compiler toolchain v5.02 for µVision Using ARM C and C++ Libraries and Floating-Point Support

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Building an application without the C library

Creating an application that has a main() function causes the C library initialization functions to be included as part of __rt_lib_init.

If your application does not have a main() function, the C library is not initialized and the following functions are not available in your application:

low-level stdio functions that have the prefix _sys_
signal-handling functions, signal() and raise() in signal.h
other functions, such as atexit().

Table 5 shows header 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.

(ARM Linux header files are not included in this table because their use serves no purpose with an uninitialized library.)

Table 5. Standalone C library functions

Function	Description
`alloca.h`	Functions in this file work without any library initialization or function re-implementation. You must know how to build an application with the C library to use this header file.
`assert.h`	Functions listed in this file require high-level stdio, `__rt_raise()`, and `_sys_exit()`. You must be familiar with tailoring error signaling, error handling, and program exit to use this header file.
`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.
`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. You must know how to build an application with the C library to use this header file. `__rt_raise()` can be re-implemented for error and exit handling. You must be familiar with tailoring error signaling, error handling, and program exit.
`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. You must be familiar with tailoring the input/output functions in the C and C++ libraries. 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 are 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.

Building an application without the C library

See also