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