You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
104 lines
4.7 KiB
HTML
104 lines
4.7 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Header Files - The C Preprocessor</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="The C Preprocessor">
|
|
<meta name="generator" content="makeinfo 4.13">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="prev" href="Overview.html#Overview" title="Overview">
|
|
<link rel="next" href="Macros.html#Macros" title="Macros">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
Copyright (C) 1987-2015 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation. A copy of
|
|
the license is included in the
|
|
section entitled ``GNU Free Documentation License''.
|
|
|
|
This manual contains no Invariant Sections. The Front-Cover Texts are
|
|
(a) (see below), and the Back-Cover Texts are (b) (see below).
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development.
|
|
-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family:serif; font-weight:normal; }
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<a name="Header-Files"></a>
|
|
<p>
|
|
Next: <a rel="next" accesskey="n" href="Macros.html#Macros">Macros</a>,
|
|
Previous: <a rel="previous" accesskey="p" href="Overview.html#Overview">Overview</a>,
|
|
Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
|
|
<hr>
|
|
</div>
|
|
|
|
<h2 class="chapter">2 Header Files</h2>
|
|
|
|
<p><a name="index-header-file-25"></a>A header file is a file containing C declarations and macro definitions
|
|
(see <a href="Macros.html#Macros">Macros</a>) to be shared between several source files. You request
|
|
the use of a header file in your program by <dfn>including</dfn> it, with the
|
|
C preprocessing directive ‘<samp><span class="samp">#include</span></samp>’.
|
|
|
|
<p>Header files serve two purposes.
|
|
|
|
<ul>
|
|
<li><a name="index-system-header-files-26"></a>System header files declare the interfaces to parts of the operating
|
|
system. You include them in your program to supply the definitions and
|
|
declarations you need to invoke system calls and libraries.
|
|
|
|
<li>Your own header files contain declarations for interfaces between the
|
|
source files of your program. Each time you have a group of related
|
|
declarations and macro definitions all or most of which are needed in
|
|
several different source files, it is a good idea to create a header
|
|
file for them.
|
|
</ul>
|
|
|
|
<p>Including a header file produces the same results as copying the header
|
|
file into each source file that needs it. Such copying would be
|
|
time-consuming and error-prone. With a header file, the related
|
|
declarations appear in only one place. If they need to be changed, they
|
|
can be changed in one place, and programs that include the header file
|
|
will automatically use the new version when next recompiled. The header
|
|
file eliminates the labor of finding and changing all the copies as well
|
|
as the risk that a failure to find one copy will result in
|
|
inconsistencies within a program.
|
|
|
|
<p>In C, the usual convention is to give header files names that end with
|
|
<samp><span class="file">.h</span></samp>. It is most portable to use only letters, digits, dashes, and
|
|
underscores in header file names, and at most one dot.
|
|
|
|
<ul class="menu">
|
|
<li><a accesskey="1" href="Include-Syntax.html#Include-Syntax">Include Syntax</a>
|
|
<li><a accesskey="2" href="Include-Operation.html#Include-Operation">Include Operation</a>
|
|
<li><a accesskey="3" href="Search-Path.html#Search-Path">Search Path</a>
|
|
<li><a accesskey="4" href="Once_002dOnly-Headers.html#Once_002dOnly-Headers">Once-Only Headers</a>
|
|
<li><a accesskey="5" href="Alternatives-to-Wrapper-_0023ifndef.html#Alternatives-to-Wrapper-_0023ifndef">Alternatives to Wrapper #ifndef</a>
|
|
<li><a accesskey="6" href="Computed-Includes.html#Computed-Includes">Computed Includes</a>
|
|
<li><a accesskey="7" href="Wrapper-Headers.html#Wrapper-Headers">Wrapper Headers</a>
|
|
<li><a accesskey="8" href="System-Headers.html#System-Headers">System Headers</a>
|
|
</ul>
|
|
|
|
</body></html>
|
|
|