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| <h4 class="subsection">11.8.1 Declare <em>and</em> Define Static Members</h4> |
| |
| <p><a name="index-C_002b_002b-static-data_002c-declaring-and-defining-3233"></a><a name="index-static-data-in-C_002b_002b_002c-declaring-and-defining-3234"></a><a name="index-declaring-static-data-in-C_002b_002b-3235"></a><a name="index-defining-static-data-in-C_002b_002b-3236"></a>When a class has static data members, it is not enough to <em>declare</em> |
| the static member; you must also <em>define</em> it. For example: |
| |
| <pre class="smallexample"> class Foo |
| { |
| ... |
| void method(); |
| static int bar; |
| }; |
| </pre> |
| <p>This declaration only establishes that the class <code>Foo</code> has an |
| <code>int</code> named <code>Foo::bar</code>, and a member function named |
| <code>Foo::method</code>. But you still need to define <em>both</em> |
| <code>method</code> and <code>bar</code> elsewhere. According to the ISO |
| standard, you must supply an initializer in one (and only one) source |
| file, such as: |
| |
| <pre class="smallexample"> int Foo::bar = 0; |
| </pre> |
| <p>Other C++ compilers may not correctly implement the standard behavior. |
| As a result, when you switch to <samp><span class="command">g++</span></samp> from one of these compilers, |
| you may discover that a program that appeared to work correctly in fact |
| does not conform to the standard: <samp><span class="command">g++</span></samp> reports as undefined |
| symbols any static data members that lack definitions. |
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