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Node:<a name="Include%20Syntax">Include Syntax</a>,
Next:<a rel="next" accesskey="n" href="Include-Operation.html#Include%20Operation">Include Operation</a>,
Up:<a rel="up" accesskey="u" href="Header-Files.html#Header%20Files">Header Files</a>
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<h3 class="section">Include Syntax</h3>
<p>Both user and system header files are included using the preprocessing
directive <code>#include</code>. It has two variants:
<dl>
<dt><code>#include <</code><var>file</var><code>></code>
<dd>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 <code>-I</code> option (see <a href="Invocation.html#Invocation">Invocation</a>).
<br><dt><code>#include "</code><var>file</var><code>"</code>
<dd>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 same directories used for <code><</code><var>file</var><code>></code>.
</dl>
<p>The argument of <code>#include</code>, 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></code> specifies inclusion of a system header file named <code>x/*y</code>.
<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"</code> specifies a filename containing three
backslashes. (Some systems interpret <code>\</code> as a pathname separator.
All of these also interpret <code>/</code> the same way. It is most portable
to use only <code>/</code>.)
<p>It is an error if there is anything (other than comments) on the line
after the file name.
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