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.