# phpman > man > intro(3)

[INTRO(3)](https://www.chedong.com/phpMan.php/man/INTRO/3/markdown)                              Linux Programmer's Manual                             [INTRO(3)](https://www.chedong.com/phpMan.php/man/INTRO/3/markdown)



## NAME
       intro - introduction to library functions

## DESCRIPTION
       Section 3 of the manual describes all library functions excluding the library functions (sys‐
       tem 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 li‐
       braries).

       In some cases, the programmer must define a feature test macro in order to obtain the  decla‐
       ration 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 fea‐
       ture test macros, see **feature**___**test**___**[macros**(7)](https://www.chedong.com/phpMan.php/man/macros/7/markdown).

## CONFORMING TO
       Certain terms and abbreviations are used to indicate UNIX variants  and  standards  to  which
       calls in this section conform.  See [**standards**(7)](https://www.chedong.com/phpMan.php/man/standards/7/markdown).

## NOTES
### 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!

## SEE ALSO
       [**intro**(2)](https://www.chedong.com/phpMan.php/man/intro/2/markdown),  [**errno**(3)](https://www.chedong.com/phpMan.php/man/errno/3/markdown),  [**capabilities**(7)](https://www.chedong.com/phpMan.php/man/capabilities/7/markdown),  [**credentials**(7)](https://www.chedong.com/phpMan.php/man/credentials/7/markdown),  [**environ**(7)](https://www.chedong.com/phpMan.php/man/environ/7/markdown),  **feature**___**test**___**[macros**(7)](https://www.chedong.com/phpMan.php/man/macros/7/markdown),
       [**libc**(7)](https://www.chedong.com/phpMan.php/man/libc/7/markdown),   **math**___**[error**(7)](https://www.chedong.com/phpMan.php/man/error/7/markdown),  **path**___**[resolution**(7)](https://www.chedong.com/phpMan.php/man/resolution/7/markdown),  [**pthreads**(7)](https://www.chedong.com/phpMan.php/man/pthreads/7/markdown),  [**signal**(7)](https://www.chedong.com/phpMan.php/man/signal/7/markdown),  [**standards**(7)](https://www.chedong.com/phpMan.php/man/standards/7/markdown),  **sys**‐‐
       **tem**___**data**___**[types**(7)](https://www.chedong.com/phpMan.php/man/types/7/markdown)

## COLOPHON
       This page is part of release 5.10 of the Linux  _man-pages_  project.   A  description  of  the
       project,  information about reporting bugs, and the latest version of this page, can be found
       at <https://www.kernel.org/doc/man-pages/>.



Linux                                        2020-11-01                                     [INTRO(3)](https://www.chedong.com/phpMan.php/man/INTRO/3/markdown)