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Standard Library - C
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The C standard library is a standardized collection of headers and library functions for the C programming language. The library provides a set of commonly used macros, type definitions, and functions to perform common tasks such as string handling, input/output processing, memory allocation, math computations, thread management, and various other common services.


Standard Headers[edit]

Related functions, necessary types to use those functions and related macros are grouped into headers. Collectively, they are known as the standard headers.

Standard C provides 29 standard headers. The headers may be included in any order. The headers may also be included more than once - the effect of that is as if it was only included once. All standard C functions have external linkage.

Optional headers[edit]

3 of the 29 standard headers are optional:

While implementations are encouraged to support those headers, they are not required to.

Detailed description[edit]

Header Name Since Description
<assert.h> C89 Provides a set of assertion macros used in assisting with debugging and detecting logic errors.
<complex.h> C99 Provides a set of functions used to manipulate complex numbers.
<ctype.h> C89 Provides a set of functions used for classifying characters.
<errno.h> C89 Provides a set of predefined values for errno.
<fenv.h> C99 Provides a set of functions for controlling the floating-point environment.
<float.h> C89 Provides a set of macros defining the implementation of the floating-point environment.
<inttypes.h> C99 Provides a set of exact width integer types.
<iso646.h> NA1 Provides a set of macros that implement an alternative way of expressing various C operators
<limits.h> C89 Provides a set of macros specifying the implementation-specific limits of the integer types.
<locale.h> C89 Provides a set of functions localization functions
<math.h> C89 Provides a set of common mathematical functions.
<setjmp.h> C89 Provides macros to perform non-local jump operators.
<signal.h> C89 Provides a set of signal handling functions.
<stdalign.h> C11 Provides a set of macros for working with object alignments.
<stdarg.h> C89 Provides a set of macros for working with variadic functions
<stdatomic.h> C11 Provides a set of functions for performing atomic operations on data.
<stdbool.h> C99 Provides boolean macros.
<stddef.h> C89 Provides a set of commonly used type definitions within the standard library.
<stdint.h> C99 Provides a set of exact width integer types.
<stdio.h> C89 Provides a set of standard input/output processing functions.
<stdlib.h> C89 Provides core library functions such as memory management and random number generation.
<stdnoreturn.h> C11 Provides a macro for specifying non-returning functions.
<string.h> C89 string handling functions.
<tgmath.h> C99 Provides a set of type-generic math functions.
<threads.h> C11 Provides a set of thread management functions.
<time.h> C89 Provides a set of date and time handling functions.
<uchar.h> C11 Provides a set of Unicode character manipulation functions.
<wchar.h> NA1 string handling functions.
<wctype.h> NA1 Provides a set of functions used for classifying wide characters.

Embedded C[edit]

Main article: Embedded C

Embedded C introduced two optional headers <stdfix.h> and <iohw.h>. The headers not formally part of the standard library.

See also[edit]