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<p>Inside a class, declares members not bound to specific instances.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="static.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="static.html#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a>
<ul>
<li class="toclevel-2 tocsection-3"><a href="static.html#Static_member_functions"><span class="tocnumber">2.1</span> <span class="toctext">Static member functions</span></a></li>
<li class="toclevel-2 tocsection-4"><a href="static.html#Static_data_members"><span class="tocnumber">2.2</span> <span class="toctext">Static data members</span></a></li>
<li class="toclevel-2 tocsection-5"><a href="static.html#Constant_static_members"><span class="tocnumber">2.3</span> <span class="toctext">Constant static members</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-6"><a href="static.html#References"><span class="tocnumber">3</span> <span class="toctext">References</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="static.html#See_also"><span class="tocnumber">4</span> <span class="toctext">See also</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span></span></span> <span class="t-spar">data_member</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span></span></span> <span class="t-spar">member_function</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<div class="t-li1"><span class="t-li">1)</span> Declares a static data member.</div>
<div class="t-li1"><span class="t-li">2)</span> Declares a static member function.</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=2" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span></h3>
<p>Static members of a class are not associated with the objects of the class: they are independent objects with <a href="storage_duration.html" title="cpp/language/storage duration">static storage duration</a> or regular functions defined in namespace scope, only once in the program.
</p><p>The <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span></span></span> keyword is only used with the declaration of a static member, inside the class definition, but not with the definition of that static member:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> X <span class="br0">{</span> <span class="kw4">static</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// declaration (uses 'static')</span>
<span class="kw4">int</span> X<span class="sy4">::</span><span class="me2">n</span> <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// definition (does not use 'static')</span></pre></div></div>
<p>The declaration inside the class body is not a definition and may declare the member to be of <a href="incomplete_type.html" title="cpp/language/incomplete type" class="mw-redirect">incomplete type</a> (other than <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>), including the type in which the member is declared:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> Foo<span class="sy4">;</span>
<span class="kw1">struct</span> S
<span class="br0">{</span>
<span class="kw4">static</span> <span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// declaration, incomplete type</span>
<span class="kw4">static</span> Foo x<span class="sy4">;</span> <span class="co1">// declaration, incomplete type</span>
<span class="kw4">static</span> S s<span class="sy4">;</span> <span class="co1">// declaration, incomplete type (inside its own definition)</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">int</span> S<span class="sy4">::</span><span class="me2">a</span><span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// definition, complete type</span>
<span class="kw1">struct</span> Foo <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
Foo S<span class="sy4">::</span><span class="me2">x</span><span class="sy4">;</span> <span class="co1">// definition, complete type</span>
S S<span class="sy4">::</span><span class="me2">s</span><span class="sy4">;</span> <span class="co1">// definition, complete type</span></pre></div></div>
<p>To refer to a static member <code>m</code> of class <code>T</code>, two forms may be used: qualified name <code>T::m</code> or member access expression <code>E.m</code> or <code>E->m</code>, where <code>E</code> is an expression that evaluates to <code>T</code> or <code>T*</code> respectively. When in the same class scope, the qualification is unnecessary:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> X
<span class="br0">{</span>
<span class="kw4">static</span> <span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// declaration</span>
<span class="kw4">static</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="co1">// declaration</span>
<span class="br0">}</span><span class="sy4">;</span>
 
X g<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> X<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="co1">// some function returning X</span>
 
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
X<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// X::f is a qualified name of static member function</span>
g<span class="br0">(</span><span class="br0">)</span>.<span class="me1">f</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// g().f is member access expression referring to a static member function</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> X<span class="sy4">::</span><span class="me2">n</span> <span class="sy1">=</span> <span class="nu0">7</span><span class="sy4">;</span> <span class="co1">// definition</span>
 
<span class="kw4">void</span> X<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="br0">)</span> <span class="co1">// definition </span>
<span class="br0">{</span>
n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// X::n is accessible as just n in this scope</span>
<span class="br0">}</span></pre></div></div>
<p>Static members obey the <a href="access.html" title="cpp/language/access">class member access rules (private, protected, public)</a>.
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=3" title="Edit section: Static member functions">edit</a>]</span> <span class="mw-headline" id="Static_member_functions">Static member functions</span></h4>
<p>Static member functions are not associated with any object. When called, they have no <span class="t-c"><span class="mw-geshi cpp source-cpp">this</span></span> pointer.
</p><p>Static member functions cannot be <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">virtual</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span>, or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">volatile</span></span></span>.
</p><p>The address of a static member function may be stored in a regular <a href="pointer.html#Pointers_to_functions" title="cpp/language/pointer">pointer to function</a>, but not in a <a href="pointer.html#Pointers_to_member_functions" title="cpp/language/pointer">pointer to member function</a>.
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=4" title="Edit section: Static data members">edit</a>]</span> <span class="mw-headline" id="Static_data_members">Static data members</span></h4>
<p>Static data members are not associated with any object. They exist even if no objects of the class have been defined. If the static member is declared thread_local<span class="t-mark-rev t-since-cxx11">(since C++11)</span>, there is one such object per thread. Otherwise, there is only one instance of the static data member in the entire program, with static <a href="storage_duration.html" title="cpp/language/storage duration">storage duration</a>.
</p><p>Static data members cannot be <span class="t-c"><span class="mw-geshi cpp source-cpp">mutable</span></span>.
</p><p>Static data members of a class in namespace scope have <a href="storage_duration.html" title="cpp/language/storage duration">external linkage</a> if the class itself has external linkage (i.e. is not a member of <a href="namespace.html#Unnamed_namespaces" title="cpp/language/namespace">unnamed namespace</a>). Local classes (classes defined inside functions) and unnamed classes, including member classes of unnamed classes, cannot have static data members.
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=5" title="Edit section: Constant static members">edit</a>]</span> <span class="mw-headline" id="Constant_static_members">Constant static members</span></h4>
<p>If a static data member of integral or enumeration type is declared <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span></span></span> (and not <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">volatile</span></span></span>), it can be initialized with a <a href="data_members.html#Member_initialization" title="cpp/language/data members">brace-or-equal initializer</a> that is a <a href="constexpr.html" title="cpp/language/constexpr">constant expression</a>, right inside the class definition:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> X
<span class="br0">{</span>
<span class="kw4">const</span> <span class="kw4">static</span> <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="kw4">const</span> <span class="kw4">static</span> <span class="kw4">int</span> m<span class="br0">{</span><span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// since C++11</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div></div>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<p>If a static data member of <a href="../concept/LiteralType.html" title="cpp/concept/LiteralType"><code>LiteralType</code></a> is declared <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span></span></span>, it can be initialized with a brace-or-equal initializer that is a constant expression, right inside the class definition:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> X <span class="br0">{</span> <span class="kw4">constexpr</span> <span class="kw4">static</span> <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span></pre></div></div>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr>
</table>
<p>If such a member is <a href="definition.html#ODR-use" title="cpp/language/definition">odr-used</a>, a definition at namespace scope is still required, but it should not have an initializer:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> X <span class="br0">{</span> <span class="kw4">const</span> <span class="kw4">static</span> <span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">const</span> <span class="kw4">int</span><span class="sy2">*</span> p <span class="sy1">=</span> <span class="sy3">&</span>X<span class="sy4">::</span><span class="me2">n</span><span class="sy4">;</span> <span class="co1">// X::n is odr-used</span>
<span class="kw4">const</span> <span class="kw4">int</span> X<span class="sy4">::</span><span class="me2">n</span><span class="sy4">;</span> <span class="co1">// … so a definition is necessary</span></pre></div></div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=6" title="Edit section: References">edit</a>]</span> <span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-c++11">
<ul><li> C++11 standard (ISO/IEC 14882:2011):
</li></ul>
<dl><dd><ul><li> 9.4 Static members [class.static]
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c++98">
<ul><li> C++98 standard (ISO/IEC 14882:1998):
</li></ul>
<dl><dd><ul><li> 9.4 Static members [class.static]
</li></ul>
</dd></dl>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/static&action=edit&section=7" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<ul><li> <a href="storage_duration.html" title="cpp/language/storage duration"><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">static</span></span></span> storage specifier</a>
</li></ul>
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