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<title>Include Syntax (The C Preprocessor)</title>

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<span id="Include-Syntax"></span><div class="header">
<p>
Next: <a href="Include-Operation.html" accesskey="n" rel="next">Include Operation</a>, Up: <a href="Header-Files.html" accesskey="u" rel="up">Header Files</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html" title="Index" rel="index">Index</a>]</p>
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<hr>
<span id="Include-Syntax-1"></span><h3 class="section">2.1 Include Syntax</h3>

<span id="index-_0023include"></span>
<p>Both user and system header files are included using the preprocessing
directive &lsquo;<samp>#include</samp>&rsquo;.  It has two variants:
</p>
<dl compact="compact">
<dt><code>#include &lt;<var>file</var>&gt;</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</a>).
</p>
</dd>
<dt><code>#include &quot;<var>file</var>&quot;</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>&lt;<var>file</var>&gt;</code>.  You can prepend directories
to the list of quote directories with the <samp>-iquote</samp> option.
</p></dd>
</dl>

<p>The argument of &lsquo;<samp>#include</samp>&rsquo;, 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&nbsp;&lt;x/*y&gt;<!-- /@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&nbsp;&quot;x\n\\y&quot;<!-- /@w --></code> specifies a filename containing three
backslashes.  (Some systems interpret &lsquo;<samp>\</samp>&rsquo; as a pathname separator.
All of these also interpret &lsquo;<samp>/</samp>&rsquo; the same way.  It is most portable
to use only &lsquo;<samp>/</samp>&rsquo;.)
</p>
<p>It is an error if there is anything (other than comments) on the line
after the file name.
</p>


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