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118 lines
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118 lines
4.8 KiB
HTML
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<head>
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<title>Static Definitions (Using the GNU Compiler Collection (GCC))</title>
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C_002b_002b-Misunderstandings.html#C_002b_002b-Misunderstandings" rel="up" title="C++ Misunderstandings">
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<link href="Name-lookup.html#Name-lookup" rel="next" title="Name lookup">
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<a name="Static-Definitions"></a>
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<div class="header">
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<p>
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Next: <a href="Name-lookup.html#Name-lookup" accesskey="n" rel="next">Name lookup</a>, Up: <a href="C_002b_002b-Misunderstandings.html#C_002b_002b-Misunderstandings" accesskey="u" rel="up">C++ Misunderstandings</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Declare-and-Define-Static-Members"></a>
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<h4 class="subsection">13.7.1 Declare <em>and</em> Define Static Members</h4>
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<a name="index-C_002b_002b-static-data_002c-declaring-and-defining"></a>
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<a name="index-static-data-in-C_002b_002b_002c-declaring-and-defining"></a>
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<a name="index-declaring-static-data-in-C_002b_002b"></a>
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<a name="index-defining-static-data-in-C_002b_002b"></a>
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<p>When a class has static data members, it is not enough to <em>declare</em>
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the static member; you must also <em>define</em> it. For example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">class Foo
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{
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…
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void method();
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static int bar;
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};
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</pre></div>
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<p>This declaration only establishes that the class <code>Foo</code> has an
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<code>int</code> named <code>Foo::bar</code>, and a member function named
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<code>Foo::method</code>. But you still need to define <em>both</em>
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<code>method</code> and <code>bar</code> elsewhere. According to the ISO
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standard, you must supply an initializer in one (and only one) source
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file, such as:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int Foo::bar = 0;
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</pre></div>
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<p>Other C++ compilers may not correctly implement the standard behavior.
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As a result, when you switch to <code>g++</code> from one of these compilers,
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you may discover that a program that appeared to work correctly in fact
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does not conform to the standard: <code>g++</code> reports as undefined
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symbols any static data members that lack definitions.
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</p>
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</body>
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</html>
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