intro — introduction to library functions


Section 3 of the manual describes all library functions excluding the library functions (system call wrappers) described in Section 2, which implement system calls.

Many of the functions described in the section are part of the Standard C Library (libc Some functions are part of other libraries (e.g., the math library, libm or the real-time library, librt in which case the manual page will indicate the linker option needed to link against the required library (e.g., −lm and −lrt, respectively, for the aforementioned libraries).

In some cases, the programmer must define a feature test macro in order to obtain the declaration of a function from the header file specified in the man page SYNOPSIS section. (Where required, these feature test macros must be defined before including any header files.) In such cases, the required macro is described in the man page. For further information on feature test macros, see feature_test_macros(7).


Certain terms and abbreviations are used to indicate UNIX variants and standards to which calls in this section conform. See standards(7).


Authors and copyright conditions

Look at the header of the manual page source for the author(s) and copyright conditions. Note that these can be different from page to page!


intro(2), errno(3), capabilities(7), credentials(7), environ(7), feature_test_macros(7), libc(7), math_error(7), path_resolution(7), pthreads(7), signal(7), standards(7)


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  Copyright (C) 2007 Michael Kerrisk <>

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2007-10-23 mtk, Nearly a complete rewrite of the earlier page.