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| 22 | <title>include Operation (GNU C Language Manual)</title>
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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-Operation"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Search-Path.html" accesskey="n" rel="next">Search Path</a>, Previous: <a href="include-Syntax.html" accesskey="p" rel="prev">include Syntax</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-Operation"></span><h4 class="subsection">26.4.2 <code>#include</code> Operation</h4>
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| 64 |
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| 65 | <p>The <code>#include</code> directive works by scanning the specified header
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| 66 | file as input before continuing with the rest of the current file.
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| 67 | The result of preprocessing consists of the text already generated,
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| 68 | followed by the result of preprocessing the included file, followed by
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| 69 | whatever results from the text after the <code>#include</code> directive.
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| 70 | For example, if you have a header file <samp>header.h</samp> as follows,
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| 71 | </p>
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| 72 | <div class="example">
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| 73 | <pre class="example">char *test (void);
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| 74 | </pre></div>
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| 75 |
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| 76 | <p>and a main program called <samp>program.c</samp> that uses the header file,
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| 77 | like this,
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| 78 | </p>
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| 79 | <div class="example">
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| 80 | <pre class="example">int x;
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| 81 | #include "header.h"
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| 82 |
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| 83 | int
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| 84 | main (void)
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| 85 | {
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| 86 | puts (test ());
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| 87 | }
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| 88 | </pre></div>
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| 89 |
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| 90 | <p>the result is equivalent to putting this text in <samp>program.c</samp>:
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| 91 | </p>
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| 92 | <div class="example">
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| 93 | <pre class="example">int x;
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| 94 | char *test (void);
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| 95 |
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| 96 | int
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| 97 | main (void)
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| 98 | {
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| 99 | puts (test ());
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| 100 | }
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| 101 | </pre></div>
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| 102 |
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| 103 | <p>Included files are not limited to declarations and macro definitions;
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| 104 | those are merely the typical uses. Any fragment of a C program can be
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| 105 | included from another file. The include file could even contain the
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| 106 | beginning of a statement that is concluded in the containing file, or
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| 107 | the end of a statement that was started in the including file. However,
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| 108 | an included file must consist of complete tokens. Comments and string
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| 109 | literals that have not been closed by the end of an included file are
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| 110 | invalid. For error recovery, the compiler terminates them at the end of
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| 111 | the file.
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| 112 | </p>
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| 113 | <p>To avoid confusion, it is best if header files contain only complete
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| 114 | syntactic units—function declarations or definitions, type
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| 115 | declarations, etc.
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| 116 | </p>
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| 117 | <p>The line following the <code>#include</code> directive is always treated as
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| 118 | a separate line, even if the included file lacks a final newline.
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| 119 | There is no problem putting a preprocessing directive there.
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| 120 | </p>
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| 121 | <hr>
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| 122 | <div class="header">
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| 123 | <p>
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| 124 | Next: <a href="Search-Path.html" accesskey="n" rel="next">Search Path</a>, Previous: <a href="include-Syntax.html" accesskey="p" rel="prev">include Syntax</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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