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| 22 | <title>Declaring an Array (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.html" rel="up" title="Arrays">
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| 33 | <link href="Strings.html" rel="next" title="Strings">
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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="Declaring-an-Array"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Strings.html" accesskey="n" rel="next">Strings</a>, Previous: <a href="Accessing-Array-Elements.html" accesskey="p" rel="prev">Accessing Array Elements</a>, Up: <a href="Arrays.html" accesskey="u" rel="up">Arrays</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="Declaring-an-Array-1"></span><h3 class="section">16.2 Declaring an Array</h3>
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| 64 | <span id="index-declaring-an-array"></span>
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| 65 | <span id="index-array_002c-declaring"></span>
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| 66 |
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| 67 | <p>To make an array declaration, write <code>[<var>length</var>]</code> after the
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| 68 | name being declared. This construct is valid in the declaration of a
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| 69 | variable, a function parameter, a function value type (the value can’t
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| 70 | be an array, but it can be a pointer to one), a structure field, or a
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| 71 | union alternative.
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| 72 | </p>
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| 73 | <p>The surrounding declaration specifies the element type of the array;
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| 74 | that can be any type of data, but not <code>void</code> or a function type.
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| 75 | For instance,
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| 76 | </p>
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| 77 | <div class="example">
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| 78 | <pre class="example">double a[5];
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| 79 | </pre></div>
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| 80 |
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| 81 | <p>declares <code>a</code> as an array of 5 <code>double</code>s.
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| 82 | </p>
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| 83 | <div class="example">
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| 84 | <pre class="example">struct foo bstruct[length];
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| 85 | </pre></div>
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| 86 |
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| 87 | <p>declares <code>bstruct</code> as an array of <code>length</code> objects of type
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| 88 | <code>struct foo</code>. A variable array size like this is allowed when
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| 89 | the array is not file-scope.
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| 90 | </p>
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| 91 | <p>Other declaration constructs can nest within the array declaration
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| 92 | construct. For instance:
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| 93 | </p>
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| 94 | <div class="example">
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| 95 | <pre class="example">struct foo *b[length];
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| 96 | </pre></div>
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| 97 |
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| 98 | <p>declares <code>b</code> as an array of <code>length</code> pointers to
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| 99 | <code>struct foo</code>. This shows that the length need not be a constant
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| 100 | (see <a href="Arrays-of-Variable-Length.html">Arrays of Variable Length</a>).
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| 101 | </p>
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| 102 | <div class="example">
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| 103 | <pre class="example">double (*c)[5];
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| 104 | </pre></div>
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| 105 |
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| 106 | <p>declares <code>c</code> as a pointer to an array of 5 <code>double</code>s, and
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| 107 | </p>
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| 108 | <div class="example">
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| 109 | <pre class="example">char *(*f (int))[5];
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| 110 | </pre></div>
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| 111 |
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| 112 | <p>declares <code>f</code> as a function taking an <code>int</code> argument and
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| 113 | returning a pointer to an array of 5 strings (pointers to
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| 114 | <code>char</code>s).
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| 115 | </p>
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| 116 | <div class="example">
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| 117 | <pre class="example">double aa[5][10];
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| 118 | </pre></div>
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| 119 |
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| 120 | <p>declares <code>aa</code> as an array of 5 elements, each of which is an
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| 121 | array of 10 <code>double</code>s. This shows how to declare a
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| 122 | multidimensional array in C (see <a href="Multidimensional-Arrays.html">Multidimensional Arrays</a>).
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| 123 | </p>
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| 124 | <p>All these declarations specify the array’s length, which is needed in
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| 125 | these cases in order to allocate storage for the array.
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| 126 | </p>
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| 127 | <hr>
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| 128 | <div class="header">
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| 129 | <p>
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| 130 | Next: <a href="Strings.html" accesskey="n" rel="next">Strings</a>, Previous: <a href="Accessing-Array-Elements.html" accesskey="p" rel="prev">Accessing Array Elements</a>, Up: <a href="Arrays.html" accesskey="u" rel="up">Arrays</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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| 131 | </div>
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