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+.\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" 2007-10-23 mtk, Nearly a complete rewrite of the earlier page.
+.TH intro 3 2023-02-05 "Linux man-pages 6.05.01"
+.SH NAME
+intro \- introduction to library functions
+.SH DESCRIPTION
+Section 3 of the manual describes all library functions
+excluding the library functions
+(system call wrappers)
+described in Section 2,
+which implement system calls.
+.PP
+Many of the functions described in the section are part of the
+Standard C Library
+.RI ( libc ).
+Some functions are part of other libraries
+(e.g.,
+the math library,
+.IR libm ,
+or the real-time library,
+.IR librt )
+in which case the manual page will indicate
+the linker option needed to link against the required library
+(e.g.,
+.I \-lm
+and
+.IR \-lrt ,
+respectively,
+for the aforementioned libraries).
+.PP
+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
+.I feature test macros
+must be defined before including
+.I any
+header files.)
+In such cases,
+the required macro is described in the man page.
+For further information on feature test macros,
+see
+.BR feature_test_macros (7).
+.\"
+.\" There
+.\" are various function groups which can be identified by a letter which
+.\" is appended to the chapter number:
+.\" .IP (3C)
+.\" These functions,
+.\" the functions from chapter 2 and from chapter 3S are
+.\" contained in the C standard library libc,
+.\" which will be used by
+.\" .BR cc (1)
+.\" by default.
+.\" .IP (3S)
+.\" These functions are parts of the
+.\" .BR stdio (3)
+.\" library.  They are contained in the standard C library libc.
+.\" .IP (3M)
+.\" These functions are contained in the arithmetic library libm.  They are
+.\" used by the
+.\" .BR f77 (1)
+.\" FORTRAN compiler by default,
+.\" but not by the
+.\" .BR cc (1)
+.\" C compiler,
+.\" which needs the option \fI\-lm\fP.
+.\" .IP (3F)
+.\" These functions are part of the FORTRAN library libF77.  There are no
+.\" special compiler flags needed to use these functions.
+.\" .IP (3X)
+.\" Various special libraries.  The manual pages documenting their functions
+.\" specify the library names.
+.SS Subsections
+Section 3 of this manual is organized into subsections
+that reflect the complex structure of the standard C library
+and its many implementations:
+.IP \[bu] 3
+3const
+.IP \[bu]
+3head
+.IP \[bu]
+3type
+.PP
+This difficult history frequently makes it a poor example to follow
+in design,
+implementation,
+and presentation.
+.PP
+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
+.IR "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.
+.SH STANDARDS
+Certain terms and abbreviations are used to indicate UNIX variants
+and standards to which calls in this section conform.
+See
+.BR standards (7).
+.SH NOTES
+.SS 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!
+.SH SEE ALSO
+.BR intro (2),
+.BR errno (3),
+.BR capabilities (7),
+.BR credentials (7),
+.BR environ (7),
+.BR feature_test_macros (7),
+.BR libc (7),
+.BR math_error (7),
+.BR path_resolution (7),
+.BR pthreads (7),
+.BR signal (7),
+.BR standards (7),
+.BR system_data_types (7)