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<html lang="en"><head><title>Using the GNU Compiler Collection (GCC)</title><meta http-equiv="Content-Type" content="text/html"><meta name="description" content="Using the GNU Compiler Collection (GCC)"><meta name="generator" content="makeinfo 4.6"><!--Copyright &copy; 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.   <p>Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with theInvariant Sections being "GNU General Public License" and "FundingFree Software", the Front-Cover texts being (a) (see below), and withthe Back-Cover Texts being (b) (see below).  A copy of the license isincluded in the section entitled "GNU Free Documentation License".   <p>(a) The FSF's Front-Cover Text is:   <p>A GNU Manual   <p>(b) The FSF's Back-Cover Text is:   <p>You have freedom to copy and modify this GNU Manual, like GNU     software.  Copies published by the Free Software Foundation raise     funds for GNU development.--><meta http-equiv="Content-Style-Type" content="text/css"><style type="text/css"><!--  pre.display { font-family:inherit }  pre.format  { font-family:inherit }  pre.smalldisplay { font-family:inherit; font-size:smaller }  pre.smallformat  { font-family:inherit; font-size:smaller }  pre.smallexample { font-size:smaller }  pre.smalllisp    { font-size:smaller }--></style></head><body><div class="node"><p>Node:&nbsp;<a name="Static%20Definitions">Static Definitions</a>,Next:&nbsp;<a rel="next" accesskey="n" href="Name-lookup.html#Name%20lookup">Name lookup</a>,Up:&nbsp;<a rel="up" accesskey="u" href="C---Misunderstandings.html#C++%20Misunderstandings">C++ Misunderstandings</a><hr><br></div><h3 class="subsection">Declare <em>and</em> Define Static Members</h4><p>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 ISOstandard, you must supply an initializer in one (and only one) sourcefile, 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 <code>g++</code> from one of these compilers,you may discover that a program that appeared to work correctly in factdoes not conform to the standard: <code>g++</code> reports as undefinedsymbols any static data members that lack definitions.   </body></html>
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