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| 22 | <title>Values from main (GNU C Language Manual)</title>
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| 30 | <link href="Symbol-Index.html" rel="index" title="Symbol Index">
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="The-main-Function.html" rel="up" title="The main Function">
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| 33 | <link href="Command_002dline-Parameters.html" rel="next" title="Command-line Parameters">
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| 57 | <body lang="en">
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| 58 | <span id="Values-from-main"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Command_002dline-Parameters.html" accesskey="n" rel="next">Command-line Parameters</a>, Up: <a href="The-main-Function.html" accesskey="u" rel="up">The main Function</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="Returning-Values-from-main"></span><h4 class="subsection">22.6.1 Returning Values from <code>main</code></h4>
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| 64 | <span id="index-returning-values-from-main"></span>
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| 65 | <span id="index-success"></span>
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| 66 | <span id="index-failure"></span>
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| 67 | <span id="index-exit-status"></span>
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| 68 |
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| 69 | <p>When <code>main</code> returns, the process terminates. Whatever value
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| 70 | <code>main</code> returns becomes the exit status which is reported to the
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| 71 | parent process. While nominally the return value is of type
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| 72 | <code>int</code>, in fact the exit status gets truncated to eight bits; if
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| 73 | <code>main</code> returns the value 256, the exit status is 0.
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| 74 | </p>
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| 75 | <p>Normally, programs return only one of two values: 0 for success,
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| 76 | and 1 for failure. For maximum portability, use the macro
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| 77 | values <code>EXIT_SUCCESS</code> and <code>EXIT_FAILURE</code> defined in
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| 78 | <code>stdlib.h</code>. Here’s an example:
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| 79 | </p>
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| 80 | <span id="index-EXIT_005fFAILURE"></span>
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| 81 | <span id="index-EXIT_005fSUCCESS"></span>
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| 82 | <div class="example">
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| 83 | <pre class="example">#include <stdlib.h> /* <span class="roman">Defines <code>EXIT_SUCCESS</code></span> */
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| 84 | /* <span class="roman">and <code>EXIT_FAILURE</code>.</span> */
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| 85 |
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| 86 | int
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| 87 | main (void)
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| 88 | {
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| 89 | <span class="roman">…</span>
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| 90 | if (foo)
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| 91 | return EXIT_SUCCESS;
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| 92 | else
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| 93 | return EXIT_FAILURE;
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| 94 | }
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| 95 | </pre></div>
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| 96 |
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| 97 | <p>Some types of programs maintain special conventions for various return
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| 98 | values; for example, comparison programs including <code>cmp</code> and
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| 99 | <code>diff</code> return 1 to indicate a mismatch, and 2 to indicate that
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| 100 | the comparison couldn’t be performed.
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| 101 | </p>
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| 102 |
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| 103 |
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| 104 |
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| 105 | </body>
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| 106 | </html>
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