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       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).

       Section 3 of this manual is organized into subsections that reflect the complex  structure
       of the standard C library and its many implementations:

       •  3const

       •  3head

       •  3type

       This  difficult  history  frequently  makes  it  a  poor  example  to  follow  in  design,
       implementation, and presentation.

       Ideally, a library for the C language is designed such that each header file presents  the
       interface  to  a  coherent  software  module.   It  provides  a  small  number of function
       declarations and exposes only data types and constants that are required for use of  those
       functions.  Together, these are termed an API or application program interface.  Types and
       constants to be shared among multiple APIs should be placed in header files  that  declare
       no  functions.   This  organization  permits a C library module to be documented concisely
       with one header file per manual page.  Such  an  approach  improves  the  readability  and
       accessibility of library documentation, and thereby the usability of the software.


       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),