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| <title>The C Preprocessor: Include Syntax</title> |
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| Next: <a href="Include-Operation.html#Include-Operation" accesskey="n" rel="next">Include Operation</a>, Up: <a href="Header-Files.html#Header-Files" accesskey="u" rel="up">Header Files</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> |
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| <a name="Include-Syntax-1"></a> |
| <h3 class="section">2.1 Include Syntax</h3> |
| |
| <a name="index-_0023include"></a> |
| <p>Both user and system header files are included using the preprocessing |
| directive ‘<samp>#include</samp>’. It has two variants: |
| </p> |
| <dl compact="compact"> |
| <dt><code>#include <<var>file</var>></code></dt> |
| <dd><p>This variant is used for system header files. It searches for a file |
| named <var>file</var> in a standard list of system directories. You can prepend |
| directories to this list with the <samp>-I</samp> option (see <a href="Invocation.html#Invocation">Invocation</a>). |
| </p> |
| </dd> |
| <dt><code>#include "<var>file</var>"</code></dt> |
| <dd><p>This variant is used for header files of your own program. It |
| searches for a file named <var>file</var> first in the directory containing |
| the current file, then in the quote directories and then the same |
| directories used for <code><<var>file</var>></code>. You can prepend directories |
| to the list of quote directories with the <samp>-iquote</samp> option. |
| </p></dd> |
| </dl> |
| |
| <p>The argument of ‘<samp>#include</samp>’, whether delimited with quote marks or |
| angle brackets, behaves like a string constant in that comments are not |
| recognized, and macro names are not expanded. Thus, <code>#include <x/*y><!-- /@w --></code> specifies inclusion of a system header file named <samp>x/*y</samp>. |
| </p> |
| <p>However, if backslashes occur within <var>file</var>, they are considered |
| ordinary text characters, not escape characters. None of the character |
| escape sequences appropriate to string constants in C are processed. |
| Thus, <code>#include "x\n\\y"<!-- /@w --></code> specifies a filename containing three |
| backslashes. (Some systems interpret ‘<samp>\</samp>’ as a pathname separator. |
| All of these also interpret ‘<samp>/</samp>’ the same way. It is most portable |
| to use only ‘<samp>/</samp>’.) |
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