Chapter 15. The Standard Headers

Each standard library function is declared in one or more of the standard headers . These headers also contain all the macro and type definitions that the C standard provides. This chapter describes the contents and use of the standard headers.

Each of the standard headers contains a set of related function declarations, macros, and type definitions. The standard headers are also called header files , as the contents of each header are usually stored in a file. Strictly speaking, however, the standard does not require the headers to be organized in files.

The C standard defines the following 24 headers. Those marked with an asterisk have been added in C99.

assert.h	inttypes.h*	signal.h	stdlib.h
complex.h*	iso646.h	stdarg.h	string.h
ctype.h	limits.h	stdbool.h*	tgmath.h*
errno.h	locale.h	stddef.h	time.h
fenv.h*	math.h	stdint.h*	wchar.h
float.h	setjmp.h	stdio.h	wctype.h