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| 22 | <title>Array Parm Pointer (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="Arrays-as-Parameters.html" rel="up" title="Arrays as Parameters">
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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="Array-Parm-Pointer"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Passing-Array-Args.html" accesskey="n" rel="next">Passing Array Args</a>, Up: <a href="Arrays-as-Parameters.html" accesskey="u" rel="up">Arrays as Parameters</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="Array-parameters-are-pointers"></span><h4 class="subsubsection">22.1.4.1 Array parameters are pointers</h4>
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| 64 |
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| 65 | <p>Declaring a function parameter variable as an array really gives it a
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| 66 | pointer type. C does this because an expression with array type, if
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| 67 | used as an argument in a function call, is converted automatically to
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| 68 | a pointer (to the zeroth element of the array). If you declare the
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| 69 | corresponding parameter as an “array”, it will work correctly with
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| 70 | the pointer value that really gets passed.
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| 71 | </p>
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| 72 | <p>This relates to the fact that C does not check array bounds in access
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| 73 | to elements of the array (see <a href="Accessing-Array-Elements.html">Accessing Array Elements</a>).
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| 74 | </p>
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| 75 | <p>For example, in this function,
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| 76 | </p>
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| 77 | <div class="example">
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| 78 | <pre class="example">void
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| 79 | clobber4 (int array[20])
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| 80 | {
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| 81 | array[4] = 0;
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| 82 | }
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| 83 | </pre></div>
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| 84 |
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| 85 | <p>the parameter <code>array</code>’s real type is <code>int *</code>; the specified
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| 86 | length, 20, has no effect on the program. You can leave out the length
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| 87 | and write this:
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| 88 | </p>
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| 89 | <div class="example">
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| 90 | <pre class="example">void
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| 91 | clobber4 (int array[])
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| 92 | {
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| 93 | array[4] = 0;
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| 94 | }
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| 95 | </pre></div>
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| 96 |
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| 97 | <p>or write the parameter declaration explicitly as a pointer:
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| 98 | </p>
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| 99 | <div class="example">
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| 100 | <pre class="example">void
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| 101 | clobber4 (int *array)
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| 102 | {
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| 103 | array[4] = 0;
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| 104 | }
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| 105 | </pre></div>
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| 106 |
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| 107 | <p>They are all equivalent.
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| 108 | </p>
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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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