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82 lines
3.7 KiB
HTML
82 lines
3.7 KiB
HTML
4 years ago
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<title>Static Definitions - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C_002b_002b-Misunderstandings.html#C_002b_002b-Misunderstandings" title="C++ Misunderstandings">
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<link rel="next" href="Name-lookup.html#Name-lookup" title="Name lookup">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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</head>
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<body>
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<div class="node">
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<a name="Static-Definitions"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Name-lookup.html#Name-lookup">Name lookup</a>,
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Up: <a rel="up" accesskey="u" href="C_002b_002b-Misunderstandings.html#C_002b_002b-Misunderstandings">C++ Misunderstandings</a>
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<hr>
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</div>
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<h4 class="subsection">12.7.1 Declare <em>and</em> Define Static Members</h4>
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<p><a name="index-C_002b_002b-static-data_002c-declaring-and-defining-4278"></a><a name="index-static-data-in-C_002b_002b_002c-declaring-and-defining-4279"></a><a name="index-declaring-static-data-in-C_002b_002b-4280"></a><a name="index-defining-static-data-in-C_002b_002b-4281"></a>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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<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>
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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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<pre class="smallexample"> int Foo::bar = 0;
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</pre>
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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 <samp><span class="command">g++</span></samp> 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: <samp><span class="command">g++</span></samp> reports as undefined
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symbols any static data members that lack definitions.
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</body></html>
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