This appendix is a summary of the library defined by the ANSI standard. The standard library is not part of the C language proper, but an environment that supports standard C will provide the function declarations and type and macro definitions of this library. We have omitted a few functions that are of limited utility or easily synthesized from others; we have omitted multi-byte characters; and we have omitted discussion of locale issues; that is, properties that depend on local language, nationality, or culture.
The functions, types and macros of the standard library are declared in standard headers:
<assert.h> <float.h> <math.h> <stdarg.h> <stdlib.h>
<ctype.h> <limits.h> <setjmp.h> <stddef.h> <string.h>
<errno.h> <locale.h> <signal.h> <stdio.h> <time.h>
A header can be accessed by
#include <header>
Headers may be included in any order and any number of times. A header must be included outside of any external declaration or definition and before any use of anything it declares. A header need not be a source file.
External identifiers that begin with an underscore are reserved for use by the library, as are all other identifiers that begin with an underscore and an upper-case letter or another underscore.