![]() The C library functions, including the ISO C standard ones, are widely used by programs, and are regarded as if they were not only an implementation of something in the C language, but also de facto part of the operating system interface. The C library is considered part of the operating system on Unix-like systems in addition to functions specified by the C standard, it includes other functions that are part of the operating system API, such as functions specified in the POSIX standard. Unix-like systems typically have a C library in shared library form, but the header files (and compiler toolchain) may be absent from an installation so C development may not be possible. ![]() On most systems, man pages on standard library functions are in section 3 section 7 may contain some more generic pages on underlying concepts (e.g. On Unix-like systems, the authoritative documentation of the API is provided in the form of man pages. A number of other groups are using other nonstandard headers – the GNU C Library has alloca.h, and HP OpenVMS has the va_count() function. ![]() Many have found their way to other architectures. The POSIX standard added several nonstandard C headers for Unix-specific functionality. Three of the header files ( complex.h, stdatomic.h, and threads.h) are conditional features that implementations are not required to support. Types and functions for manipulating Unicode charactersĭefines set of functions used to classify wide characters by their types or to convert between upper and lower case For programming in ISO 646 variant character sets.ĭefines macro constants specifying the implementation-specific properties of the integer types.ĭeclares the macros setjmp and longjmp, which are used for non-local exits.įor querying and specifying the alignment of objects.įor accessing a varying number of arguments passed to functions.įor atomic operations on data shared between threads.ĭefines numeric conversion functions, pseudo-random numbers generation functions, memory allocation, process control functionsĭefines type-generic mathematical functions.ĭefines functions for managing multiple threads, mutexes and condition variablesĭefines date- and time-handling functions In total, there are now 29 header files:ĭeclares the assert macro, used to assist with detecting logical errors and other types of bugs while debugging a program.ĭefines a set of functions for manipulating complex numbers.ĭefines set of functions used to classify characters by their types or to convert between upper and lower case in a way that is independent of the used character set (typically ASCII or one of its extensions, although implementations utilizing EBCDIC are also known).įor testing error codes reported by library functions.ĭefines a set of functions for controlling floating-point environment.ĭefines macro constants specifying the implementation-specific properties of the floating-point library.ĭefines several macros that implement alternative ways to express several standard tokens. Six more header files ( complex.h, fenv.h, inttypes.h, stdbool.h, stdint.h, and tgmath.h) were added with C99, a revision to the C Standard published in 1999, and five more files ( stdalign.h, stdatomic.h, stdnoreturn.h, threads.h, and uchar.h) with C11 in 2011. Each header file contains one or more function declarations, data type definitions, and macros.Īfter a long period of stability, three new header files ( iso646.h, wchar.h, and wctype.h) were added with Normative Addendum 1 (NA1), an addition to the C Standard ratified in 1995. The application programming interface (API) of the C standard library is declared in a number of header files. The C standard library provides macros, type definitions and functions for tasks such as string handling, mathematical computations, input/output processing, memory management, and several other operating system services.Īpplication programming interface (API) Header files ![]() Since ANSI C was adopted by the International Organization for Standardization, the C standard library is also called the ISO C library. Starting from the original ANSI C standard, it was developed at the same time as the C library POSIX specification, which is a superset of it. The C standard library or libc is the standard library for the C programming language, as specified in the ISO C standard.
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