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| 22 | <title>Flexible Array Fields (GNU C Language Manual)</title>
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| 55 | </head>
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| 57 | <body lang="en">
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| 58 | <span id="Flexible-Array-Fields"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Overlaying-Structures.html" accesskey="n" rel="next">Overlaying Structures</a>, Previous: <a href="Zero-Length.html" accesskey="p" rel="prev">Zero Length</a>, Up: <a href="Structures.html" accesskey="u" rel="up">Structures</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="Flexible-Array-Fields-1"></span><h3 class="section">15.10 Flexible Array Fields</h3>
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| 64 | <span id="index-flexible-array-fields"></span>
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| 65 | <span id="index-array-fields_002c-flexible"></span>
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| 66 |
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| 67 | <p>The C99 standard adopted a more complex equivalent of zero-length
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| 68 | array fields. It’s called a <em>flexible array</em>, and it’s indicated
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| 69 | by omitting the length, like this:
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| 70 | </p>
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| 71 | <div class="example">
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| 72 | <pre class="example">struct line
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| 73 | {
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| 74 | int length;
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| 75 | char contents[];
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| 76 | };
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| 77 | </pre></div>
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| 78 |
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| 79 | <p>The flexible array has to be the last field in the structure, and there
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| 80 | must be other fields before it.
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| 81 | </p>
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| 82 | <p>Under the C standard, a structure with a flexible array can’t be part
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| 83 | of another structure, and can’t be an element of an array.
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| 84 | </p>
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| 85 | <p>GNU C allows static initialization of flexible array fields. The effect
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| 86 | is to “make the array long enough” for the initializer.
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| 87 | </p>
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| 88 | <div class="example">
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| 89 | <pre class="example">struct f1 { int x; int y[]; } f1
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| 90 | = { 1, { 2, 3, 4 } };
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| 91 | </pre></div>
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| 92 |
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| 93 | <p>This defines a structure variable named <code>f1</code>
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| 94 | whose type is <code>struct f1</code>. In C, a variable name or function name
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| 95 | never conflicts with a structure type tag.
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| 96 | </p>
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| 97 | <p>Omitting the flexible array field’s size lets the initializer
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| 98 | determine it. This is allowed only when the flexible array is defined
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| 99 | in the outermost structure and you declare a variable of that
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| 100 | structure type. For example:
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| 101 | </p>
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| 102 | <div class="example">
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| 103 | <pre class="example">struct foo { int x; int y[]; };
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| 104 | struct bar { struct foo z; };
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| 105 |
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| 106 | struct foo a = { 1, { 2, 3, 4 } }; // <span class="roman">Valid.</span>
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| 107 | struct bar b = { { 1, { 2, 3, 4 } } }; // <span class="roman">Invalid.</span>
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| 108 | struct bar c = { { 1, { } } }; // <span class="roman">Valid.</span>
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| 109 | struct foo d[1] = { { 1 { 2, 3, 4 } } }; // <span class="roman">Invalid.</span>
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| 110 | </pre></div>
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| 111 |
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| 112 |
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| 113 |
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| 114 |
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