Components of the C library

The programming interface of the C runtime library supports more than 500 predefined functions (see also the table on "Scope of the supported C library"). These functions are available either as source program fragments (macros) or in the form of precompiled program segments (modules). The function declarations, definitions of constants, data types and macros, and the function macros themselves are incorporated in "header files" (also called "include files" or simply "headers").