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| 22 | <title>Old-Style Function Definitions (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="Obsolete-Definitions.html" rel="up" title="Obsolete Definitions">
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| 57 | <body lang="en">
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| 58 | <span id="Old_002dStyle-Function-Definitions"></span><div class="header">
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| 59 | <p>
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| 60 | Previous: <a href="Old-GNU-Inlining.html" accesskey="p" rel="prev">Old GNU Inlining</a>, Up: <a href="Obsolete-Definitions.html" accesskey="u" rel="up">Obsolete Definitions</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="Old_002dStyle-Function-Definitions-1"></span><h4 class="subsection">22.8.2 Old-Style Function Definitions</h4>
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| 64 | <span id="index-old_002dstyle-function-definitions"></span>
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| 65 | <span id="index-function-definitions_002c-old_002dstyle"></span>
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| 66 | <span id="index-K_0026R_002dstyle-function-definitions"></span>
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| 67 |
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| 68 | <p>The syntax of C traditionally allows omitting the data type in a
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| 69 | function declaration if it specifies a storage class or a qualifier.
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| 70 | Then the type defaults to <code>int</code>. For example:
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| 71 | </p>
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| 72 | <div class="example">
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| 73 | <pre class="example">static foo (double x);
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| 74 | </pre></div>
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| 75 |
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| 76 | <p>defaults the return type to <code>int</code>. This is bad practice; if you
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| 77 | see it, fix it.
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| 78 | </p>
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| 79 | <p>An <em>old-style</em> (or “K&R”) function definition is the way
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| 80 | function definitions were written in the 1980s. It looks like this:
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| 81 | </p>
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| 82 | <div class="example">
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| 83 | <pre class="example"><var>rettype</var>
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| 84 | <var>function</var> (<var>parmnames</var>)
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| 85 | <var>parm_declarations</var>
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| 86 | {
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| 87 | <var>body</var>
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| 88 | }
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| 89 | </pre></div>
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| 90 |
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| 91 | <p>In <var>parmnames</var>, only the parameter names are listed, separated by
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| 92 | commas. Then <var>parm_declarations</var> declares their data types; these
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| 93 | declarations look just like variable declarations. If a parameter is
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| 94 | listed in <var>parmnames</var> but has no declaration, it is implicitly
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| 95 | declared <code>int</code>.
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| 96 | </p>
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| 97 | <p>There is no reason to write a definition this way nowadays, but they
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| 98 | can still be seen in older GNU programs.
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| 99 | </p>
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| 100 | <p>An old-style variadic function definition looks like this:
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| 101 | </p>
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| 102 | <div class="example">
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| 103 | <pre class="example">#include <varargs.h>
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| 104 |
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| 105 | int
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| 106 | add_multiple_values (va_alist)
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| 107 | va_dcl
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| 108 | {
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| 109 | int argcount;
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| 110 | int counter, total = 0;
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| 111 |
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| 112 | /* <span class="roman">Declare a variable of type <code>va_list</code>.</span> */
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| 113 | va_list argptr;
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| 114 |
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| 115 | /* <span class="roman">Initialize that variable.</span> */
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| 116 | va_start (argptr);
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| 117 |
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| 118 | /* <span class="roman">Get the first argument (fixed).</span> */
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| 119 | argcount = va_arg (int);
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| 120 |
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| 121 | for (counter = 0; counter < argcount; counter++)
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| 122 | {
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| 123 | /* <span class="roman">Get the next additional argument.</span> */
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| 124 | total += va_arg (argptr, int);
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| 125 | }
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| 126 |
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| 127 | /* <span class="roman">End use of the <code>argptr</code> variable.</span> */
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| 128 | va_end (argptr);
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| 129 |
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| 130 | return total;
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| 131 | }
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| 132 | </pre></div>
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| 133 |
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| 134 | <p>Note that the old-style variadic function definition has no fixed
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| 135 | parameter variables; all arguments must be obtained with
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| 136 | <code>va_arg</code>.
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| 137 | </p>
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| 138 |
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| 139 |
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| 140 |
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| 141 | </body>
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| 142 | </html>
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