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| 22 | <title>Labels as Values (GNU C Language Manual)</title>
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| 23 |
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| 24 | <meta name="description" content="Labels as Values (GNU C Language Manual)">
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| 31 | <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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| 32 | <link href="Statements.html" rel="up" title="Statements">
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| 33 | <link href="Label-Value-Uses.html" rel="next" title="Label Value Uses">
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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="Labels-as-Values"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Statement-Exprs.html" accesskey="n" rel="next">Statement Exprs</a>, Previous: <a href="Local-Labels.html" accesskey="p" rel="prev">Local Labels</a>, Up: <a href="Statements.html" accesskey="u" rel="up">Statements</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="Labels-as-Values-1"></span><h3 class="section">19.14 Labels as Values</h3>
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| 64 | <span id="index-labels-as-values"></span>
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| 65 | <span id="index-computed-gotos"></span>
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| 66 | <span id="index-goto-with-computed-label"></span>
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| 67 | <span id="index-address-of-a-label"></span>
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| 68 |
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| 69 | <p>In GNU C, you can get the address of a label defined in the current
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| 70 | function (or a local label defined in the containing function) with
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| 71 | the unary operator ‘<samp>&&</samp>’. The value has type <code>void *</code>. This
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| 72 | value is a constant and can be used wherever a constant of that type
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| 73 | is valid. For example:
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| 74 | </p>
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| 75 | <div class="example">
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| 76 | <pre class="example">void *ptr;
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| 77 | <span class="roman">…</span>
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| 78 | ptr = &&foo;
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| 79 | </pre></div>
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| 80 |
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| 81 | <p>To use these values requires a way to jump to one. This is done
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| 82 | with the computed goto statement<a id="DOCF5" href="#FOOT5"><sup>5</sup></a>, <code>goto *<var>exp</var>;</code>. For example,
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| 83 | </p>
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| 84 | <div class="example">
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| 85 | <pre class="example">goto *ptr;
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| 86 | </pre></div>
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| 87 |
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| 88 | <p>Any expression of type <code>void *</code> is allowed.
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| 89 | </p>
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| 90 | <p>See <a href="goto-Statement.html">goto Statement</a>.
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| 91 | </p>
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| 92 | <table class="menu" border="0" cellspacing="0">
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| 93 | <tr><td align="left" valign="top">• <a href="Label-Value-Uses.html" accesskey="1">Label Value Uses</a></td><td> </td><td align="left" valign="top">Examples of using label values.
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| 94 | </td></tr>
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| 95 | <tr><td align="left" valign="top">• <a href="Label-Value-Caveats.html" accesskey="2">Label Value Caveats</a></td><td> </td><td align="left" valign="top">Limitations of label values.
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| 96 | </td></tr>
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| 97 | </table>
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| 98 |
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| 99 | <div class="footnote">
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| 100 | <hr>
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| 101 | <h4 class="footnotes-heading">Footnotes</h4>
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| 102 |
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| 103 | <h5><a id="FOOT5" href="#DOCF5">(5)</a></h3>
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| 104 | <p>The analogous feature in
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| 105 | Fortran is called an assigned goto, but that name seems inappropriate in
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| 106 | C, since you can do more with label addresses than store them in special label
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| 107 | variables.</p>
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| 108 | </div>
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| 109 |
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| 110 |
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| 111 |
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| 112 | </body>
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| 113 | </html>
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