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| 22 | <title>Unnamed Types as Fields (GNU C Language Manual)</title>
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| 24 | <meta name="description" content="Unnamed Types as Fields (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="Structures.html" rel="up" title="Structures">
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| 33 | <link href="Incomplete-Types.html" rel="next" title="Incomplete Types">
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| 56 |
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| 57 | <body lang="en">
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| 58 | <span id="Unnamed-Types-as-Fields"></span><div class="header">
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| 59 | <p>
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| 60 | Next: <a href="Incomplete-Types.html" accesskey="n" rel="next">Incomplete Types</a>, Previous: <a href="Structure-Constructors.html" accesskey="p" rel="prev">Structure Constructors</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="Unnamed-Types-as-Fields-1"></span><h3 class="section">15.17 Unnamed Types as Fields</h3>
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| 64 | <span id="index-unnamed-structures"></span>
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| 65 | <span id="index-unnamed-unions"></span>
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| 66 | <span id="index-structures_002c-unnamed"></span>
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| 67 | <span id="index-unions_002c-unnamed"></span>
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| 68 |
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| 69 | <p>A structure or a union can contain, as fields,
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| 70 | unnamed structures and unions. Here’s an example:
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| 71 | </p>
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| 72 | <div class="example">
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| 73 | <pre class="example">struct
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| 74 | {
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| 75 | int a;
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| 76 | union
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| 77 | {
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| 78 | int b;
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| 79 | float c;
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| 80 | };
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| 81 | int d;
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| 82 | } foo;
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| 83 | </pre></div>
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| 84 |
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| 85 | <p>You can access the fields of the unnamed union within <code>foo</code> as if they
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| 86 | were individual fields at the same level as the union definition:
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| 87 | </p>
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| 88 | <div class="example">
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| 89 | <pre class="example">foo.a = 42;
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| 90 | foo.b = 47;
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| 91 | foo.c = 5.25; // <span class="roman">Overwrites the value in <code>foo.b</code></span>.
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| 92 | foo.d = 314;
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| 93 | </pre></div>
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| 94 |
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| 95 | <p>Avoid using field names that could cause ambiguity. For example, with
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| 96 | this definition:
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| 97 | </p>
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| 98 | <div class="example">
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| 99 | <pre class="example">struct
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| 100 | {
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| 101 | int a;
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| 102 | struct
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| 103 | {
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| 104 | int a;
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| 105 | float b;
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| 106 | };
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| 107 | } foo;
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| 108 | </pre></div>
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| 109 |
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| 110 | <p>it is impossible to tell what <code>foo.a</code> refers to. GNU C reports
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| 111 | an error when a definition is ambiguous in this way.
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| 112 | </p>
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| 113 |
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| 114 |
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| 115 |
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| 116 | </body>
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