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| 22 | <title>include Syntax (GNU C Language Manual)</title>
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Header-Files.html" rel="up" title="Header Files">
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| 33 | <link href="include-Operation.html" rel="next" title="include Operation">
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| 55 | </head>
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="include-Syntax"></span><div class="header">
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| 59 | <p>
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| 60 | 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> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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| 61 | </div>
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| 62 | <hr>
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| 63 | <span id="g_t_0023include-Syntax"></span><h4 class="subsection">26.4.1 <code>#include</code> Syntax</h4>
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| 64 |
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| 65 | <span id="index-_0023include"></span>
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| 66 | <p>You can specify inclusion of user and system header files with the
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| 67 | preprocessing directive <code>#include</code>. It has two variants:
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| 68 | </p>
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| 69 | <dl compact="compact">
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| 70 | <dt><code>#include <<var>file</var>></code></dt>
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| 71 | <dd><p>This variant is used for system header files. It searches for a file
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| 72 | named <var>file</var> in a standard list of system directories. You can
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| 73 | prepend directories to this list with the <samp>-I</samp> option
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| 74 | (see <a href="https://gcc.gnu.org/onlinedocs/gcc/Invocation.html#Invocation">Invoking GCC</a> in <cite>Using the GNU
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| 75 | Compiler Collection</cite>).
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| 76 | </p>
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| 77 | </dd>
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| 78 | <dt><code>#include "<var>file</var>"</code></dt>
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| 79 | <dd><p>This variant is used for header files of your own program. It
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| 80 | searches for a file named <var>file</var> first in the directory containing
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| 81 | the current file, then in the quote directories, then the same
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| 82 | directories used for <code><<var>file</var>></code>. You can prepend directories
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| 83 | to the list of quote directories with the <samp>-iquote</samp> option.
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| 84 | </p></dd>
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| 85 | </dl>
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| 86 |
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| 87 | <p>The argument of <code>#include</code>, whether delimited with quote marks or
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| 88 | angle brackets, behaves like a string constant in that comments are not
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| 89 | 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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| 90 | </p>
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| 91 | <p>However, if backslashes occur within <var>file</var>, they are considered
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| 92 | ordinary text characters, not escape characters: character escape
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| 93 | sequences such as used in string constants in C are not meaningful
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| 94 | here. Thus, <code>#include "x\n\\y"<!-- /@w --></code> specifies a filename
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| 95 | containing three backslashes. By the same token, there is no way to
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| 96 | escape ‘<samp>"</samp>’ or ‘<samp>></samp>’ to include it in the header file name if
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| 97 | it would instead end the file name.
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| 98 | </p>
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| 99 | <p>Some systems interpret ‘<samp>\</samp>’ as a file name component separator.
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| 100 | All these systems also interpret ‘<samp>/</samp>’ the same way. It is most
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| 101 | portable to use only ‘<samp>/</samp>’.
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| 102 | </p>
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| 103 | <p>It is an error to put anything other than comments on the
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| 104 | <code>#include</code> line after the file name.
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| 105 | </p>
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| 106 | <hr>
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| 107 | <div class="header">
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| 108 | <p>
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| 109 | 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> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Index.html" title="Index" rel="index">Index</a>]</p>
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