| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- 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. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>The C Preprocessor: Header Files</title> |
| |
| <meta name="description" content="The C Preprocessor: Header Files"> |
| <meta name="keywords" content="The C Preprocessor: Header Files"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="index.html#Top" rel="up" title="Top"> |
| <link href="Include-Syntax.html#Include-Syntax" rel="next" title="Include Syntax"> |
| <link href="The-preprocessing-language.html#The-preprocessing-language" rel="prev" title="The preprocessing language"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Header-Files"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Overview.html#Overview" accesskey="p" rel="prev">Overview</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Header-Files-1"></a> |
| <h2 class="chapter">2 Header Files</h2> |
| |
| <a name="index-header-file"></a> |
| <p>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 <em>including</em> it, with the |
| C preprocessing directive ‘<samp>#include</samp>’. |
| </p> |
| <p>Header files serve two purposes. |
| </p> |
| <ul> |
| <li> <a name="index-system-header-files"></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><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. |
| </li></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> |
| <p>In C, the usual convention is to give header files names that end with |
| <samp>.h</samp>. It is most portable to use only letters, digits, dashes, and |
| underscores in header file names, and at most one dot. |
| </p> |
| <table class="menu" border="0" cellspacing="0"> |
| <tr><td align="left" valign="top">• <a href="Include-Syntax.html#Include-Syntax" accesskey="1">Include Syntax</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Include-Operation.html#Include-Operation" accesskey="2">Include Operation</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Search-Path.html#Search-Path" accesskey="3">Search Path</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" accesskey="4">Once-Only Headers</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Alternatives-to-Wrapper-_0023ifndef.html#Alternatives-to-Wrapper-_0023ifndef" accesskey="5">Alternatives to Wrapper #ifndef</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Computed-Includes.html#Computed-Includes" accesskey="6">Computed Includes</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="Wrapper-Headers.html#Wrapper-Headers" accesskey="7">Wrapper Headers</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| <tr><td align="left" valign="top">• <a href="System-Headers.html#System-Headers" accesskey="8">System Headers</a>:</td><td> </td><td align="left" valign="top"> |
| </td></tr> |
| </table> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Overview.html#Overview" accesskey="p" rel="prev">Overview</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
