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<tr class="t-nv"><td colspan="5"> <a href="operator_comparison.html" title="cpp/language/operator comparison"> Comparison operators</a>: <code>a==b</code>, <code>a!=b</code>, <code>a<b</code>, <code>a>b</code>, <code>a<=b</code>, <code>a>=b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_member_access.html" title="cpp/language/operator member access"> Member access operators</a>: <code>a[b]</code>, <code>*a</code>, <code>&a</code>, <code>a->b</code>, <code>a.b</code>, <code>a->*b</code>, <code>a.*b</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_other.html" title="cpp/language/operator other"> Other operators</a>: <code>a(...)</code>, <code>a,b</code>, <code>a?b:c</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_alternative.html" title="cpp/language/operator alternative">Alternative representations of operators</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_precedence.html" title="cpp/language/operator precedence">Precedence and associativity</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="fold.html" title="cpp/language/fold">Fold expression</a><span class="t-mark-rev t-since-cxx17">(C++17)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="new.html" title="cpp/language/new">new-expression</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="delete.html" title="cpp/language/delete">delete-expression</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="throw.html" title="cpp/language/throw">throw-expression</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="alignof.html" title="cpp/language/alignof">alignof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof.html" title="cpp/language/sizeof">sizeof</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="sizeof....html" title="cpp/language/sizeof...">sizeof...</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="typeid.html" title="cpp/language/typeid">typeid</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="noexcept.html" title="cpp/language/noexcept">noexcept</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operators.html" title="cpp/language/operators">Operator overloading</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Conversions </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="implicit_cast.html" title="cpp/language/implicit cast">Implicit conversions</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="const_cast.html" title="cpp/language/const cast">const_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static_cast.html" title="cpp/language/static cast">static_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast">reinterpret_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="dynamic_cast.html" title="cpp/language/dynamic cast">dynamic_cast</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="explicit_cast.html" title="cpp/language/explicit cast">Explicit conversions</a> <code>(T)a</code>, <code>T(a)</code></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="cast_operator.html" title="cpp/language/cast operator">User-defined conversion</a></td></tr>
</table></div>
</div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/language/expressions/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>Each C++ <a href="expressions.html" title="cpp/language/expressions">expression</a> (an operator with its operands, a literal, a variable name, etc.) is characterized by two independent properties: a <i>type</i> and a <i>value category</i>. Each expression has some non-reference type, and each expression belongs to exactly one of the three primary value categories.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="value_category.html#Primary_categories"><span class="tocnumber">1</span> <span class="toctext">Primary categories</span></a>
<ul>
<li class="toclevel-2 tocsection-2"><a href="value_category.html#lvalue"><span class="tocnumber">1.1</span> <span class="toctext">lvalue</span></a></li>
<li class="toclevel-2 tocsection-3"><a href="value_category.html#rvalue_.28until_C.2B.2B11.29prvalue_.28since_C.2B.2B11.29"><span class="tocnumber">1.2</span> <span class="toctext"><span><span>rvalue</span> <span><span>(until C++11)</span></span></span><span><span>prvalue</span> <span><span>(since C++11)</span></span></span></span></a></li>
<li class="toclevel-2"><a href="value_category.html#xvalue"><span class="tocnumber">1.3</span> <span class="toctext">xvalue</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-5"><a href="value_category.html#Mixed_categories"><span class="tocnumber">2</span> <span class="toctext">Mixed categories</span></a>
<ul>
<li class="toclevel-2 tocsection-6"><a href="value_category.html#glvalue"><span class="tocnumber">2.1</span> <span class="toctext">glvalue</span></a></li>
<li class="toclevel-2 tocsection-7"><a href="value_category.html#rvalue"><span class="tocnumber">2.2</span> <span class="toctext">rvalue</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-8"><a href="value_category.html#Special_categories"><span class="tocnumber">3</span> <span class="toctext">Special categories</span></a>
<ul>
<li class="toclevel-2 tocsection-9"><a href="value_category.html#Pending_member_function_call"><span class="tocnumber">3.1</span> <span class="toctext">Pending member function call</span></a></li>
<li class="toclevel-2 tocsection-10"><a href="value_category.html#Void_expressions"><span class="tocnumber">3.2</span> <span class="toctext">Void expressions</span></a></li>
<li class="toclevel-2 tocsection-11"><a href="value_category.html#Bit_fields"><span class="tocnumber">3.3</span> <span class="toctext">Bit fields</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-12"><a href="value_category.html#Footnotes"><span class="tocnumber">4</span> <span class="toctext">Footnotes</span></a>
<ul>
<li class="toclevel-2 tocsection-13"><a href="value_category.html#External_references"><span class="tocnumber">4.1</span> <span class="toctext">External references</span></a></li>
<li class="toclevel-2 tocsection-14"><a href="value_category.html#Defect_reports"><span class="tocnumber">4.2</span> <span class="toctext">Defect reports</span></a></li>
<li class="toclevel-2 tocsection-15"><a href="value_category.html#See_also"><span class="tocnumber">4.3</span> <span class="toctext">See also</span></a></li>
</ul>
</li>
</ul>
</td></tr></table>
<h2><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=1" title="Edit section: Primary categories">edit</a>]</span> <span class="mw-headline" id="Primary_categories">Primary categories</span></h2>
<p>The primary value categories correspond to two properties of expressions:
</p>
<ul><li> <i>has identity</i>: it's possible to determine whether the expression refers to the same entity as another expression, such as by comparing addresses of the objects or functions they identify (obtained directly or indirectly);
</li><li> <i>can be moved from</i>: <a href="move_constructor.html" title="cpp/language/move constructor">move constructor</a>, <a href="move_operator.html" title="cpp/language/move operator" class="mw-redirect">move assignment operator</a>, or another function overload that implements move semantics can bind to the expression.
</li></ul>
<p>Expressions that:
</p>
<ul><li> have identity and cannot be moved from are called <i>lvalue expressions</i>;
</li><li> have identity and can be moved from are called <i>xvalue expressions</i>;
</li><li> do not have identity and can be moved from are called <i>prvalue expressions</i>;
</li><li> do not have identity and cannot be moved from are not used.
</li></ul>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=2" title="Edit section: lvalue">edit</a>]</span> <span class="mw-headline" id="lvalue">lvalue</span></h3>
<p>An <i>lvalue</i> ("left value") expression is an expression that <i>has identity</i> and <i>cannot be moved from</i>. The naming is historic and reflects the use of lvalue expressions as the left-hand operand of the assignment operator in the CPL programming language.
</p><p>The following expressions are lvalue expressions:
</p>
<ul><li> the name of a variable or function in scope, regardless of type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/cin.html"><span class="kw1479">std::<span class="me2">cin</span></span></a></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/manip/endl.html"><span class="kw1514">std::<span class="me2">endl</span></span></a></span></span>. Even if the variable's type is rvalue reference, the expression consisting of its name is an lvalue expression;
</li><li> a function call or an overloaded operator expression of lvalue reference return type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../string/basic_string/getline.html"><span class="kw1080">std::<span class="me2">getline</span></span></a><span class="br0">(</span><a href="../io/cin.html"><span class="kw1479">std::<span class="me2">cin</span></span></a>, str<span class="br0">)</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/cout.html"><span class="kw1481">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="nu0">1</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">str1 <span class="sy1">=</span> str2</span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>it</span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">=</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">+</span><span class="sy1">=</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">%</span><span class="sy1">=</span> b</span></span>, and all other built-in <a href="operator_assignment.html" title="cpp/language/operator assignment">assignment and compound assignment</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a</span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">--</span>a</span></span>, the built-in <a href="operator_incdec.html#Built-in_prefix_operators" title="cpp/language/operator incdec">pre-increment and pre-decrement</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>p</span></span>, the built-in <a href="operator_member_access.html#Built-in_indirection_operator" title="cpp/language/operator member access">indirection</a> expression;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>n<span class="br0">]</span></span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="br0">[</span>n<span class="br0">]</span></span></span>, the built-in <a href="operator_member_access.html#Built-in_subscript_operator" title="cpp/language/operator member access">subscript</a> expressions<span class="t-rev-inl t-since-cxx11"><span>, except where <code>a</code> is an array rvalue</span> <span><span class="t-mark-rev t-since-cxx11">(since C++11)</span></span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">m</span></span></span>, the <a href="operator_member_access.html#Built-in_member_access_operators" title="cpp/language/operator member access">member of object</a> expression, except where <code>m</code> is a member enumerator or non-static member function, or where <code>a</code> is an rvalue and <code>m</code> is a non-static data member of non-reference type;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span>m</span></span>, the built-in <a href="operator_member_access.html#Built-in_member_access_operators" title="cpp/language/operator member access">member of pointer</a> expression, except where <code>m</code> is a member enumerator or non-static member function;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="sy2">*</span>mp</span></span>, the <a href="operator_member_access.html#Built-in_pointer-to-member_access_operators" title="cpp/language/operator member access">pointer to member of object</a> expression, where <code>a</code> is an lvalue and <code>mp</code> is a pointer to data member;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span><span class="sy2">*</span>mp</span></span>, the built-in <a href="operator_member_access.html#Built-in_pointer-to-member_access_operators" title="cpp/language/operator member access">pointer to member of pointer</a> expression, where <code>mp</code> is a pointer to data member;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a, b</span></span>, the built-in <a href="operator_other.html#Built-in_comma_operator" title="cpp/language/operator other">comma</a> expression, where <code>b</code> is an lvalue;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy4">?</span> b <span class="sy4">:</span> c</span></span>, the <a href="operator_other.html#Conditional_operator" title="cpp/language/operator other">ternary conditional</a> expression for some <code>a</code>, <code>b</code>, and <code>c</code>;
</li><li> a <a href="string_literal.html" title="cpp/language/string literal">string literal</a>, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"Hello, world!"</span></span></span>;
</li><li> a cast expression to lvalue reference type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span>x<span class="br0">)</span></span></span>;
</li></ul>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<ul><li> a cast expression to rvalue reference to function type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">void</span> <span class="br0">(</span><span class="sy3">&&</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span>x<span class="br0">)</span></span></span>;
</li><li> a function call or overloaded operator expression of rvalue reference to function return type.
</li></ul>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr>
</table>
<p>Properties:
</p>
<ul><li> Same as glvalue (below).
</li><li> Address of an lvalue may be taken: <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><span class="sy2">++</span>i</span></span><sup id="cite_ref-1" class="reference"><a href="value_category.html#cite_note-1">[1]</a></sup> and <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><a href="../io/manip/endl.html"><span class="kw1514">std::<span class="me2">endl</span></span></a></span></span> are valid expressions.
</li><li> A modifiable lvalue may be used as the left-hand operand of the built-in assignment operator.
</li><li> An lvalue may be used to <a href="reference_initialization.html" title="cpp/language/reference initialization">initialize an lvalue reference</a>; this associates a new name with the object identified by the expression.
</li></ul>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=3" title="Edit section: rvalue (until C++11)prvalue (since C++11)">edit</a>]</span> <span class="mw-headline" id="rvalue_.28until_C.2B.2B11.29prvalue_.28since_C.2B.2B11.29"><span class="t-rev-inl t-until-cxx11"><span>rvalue</span> <span><span class="t-mark-rev t-until-cxx11">(until C++11)</span></span></span><span class="t-rev-inl t-since-cxx11"><span>prvalue</span> <span><span class="t-mark-rev t-since-cxx11">(since C++11)</span></span></span></span></h3>
<p>A <i>prvalue</i> ("pure rvalue") expression is an expression that <i>does not have identity</i> and <i>can be moved from</i>.
</p><p>The following expressions are prvalue expressions:
</p>
<ul><li> a <a href="expressions.html#Literals" title="cpp/language/expressions">literal</a> (except for <a href="string_literal.html" title="cpp/language/string literal">string literal</a>), such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">42</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span>;
</li><li> a function call or an overloaded operator expression of non-reference return type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">substr</span><span class="br0">(</span><span class="nu0">1</span>, <span class="nu0">2</span><span class="br0">)</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">str1 <span class="sy2">+</span> str2</span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp">it<span class="sy2">++</span></span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="sy2">++</span></span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="sy2">--</span></span></span>, the built-in <a href="operator_incdec.html#Built-in_postfix_operators" title="cpp/language/operator incdec">post-increment and post-decrement</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">+</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy2">%</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy3">&</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1"><<</span> b</span></span>, and all other built-in <a href="operator_arithmetic.html" title="cpp/language/operator arithmetic">arithmetic</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy3">&&</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy3">||</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">~a</span></span>, the built-in <a href="operator_logical.html" title="cpp/language/operator logical">logical</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1"><</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b</span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">>=</span> b</span></span>, and all other built-in <a href="operator_comparison.html" title="cpp/language/operator comparison">comparison</a> expressions;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span>a</span></span>, the built-in <a href="operator_member_access.html#Built-in_address-of_operator" title="cpp/language/operator member access">address-of</a> expression;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">m</span></span></span>, the <a href="operator_member_access.html#Built-in_member_access_operators" title="cpp/language/operator member access">member of object</a> expression, where <code>m</code> is a member enumerator or a non-static member function<sup id="cite_ref-pmfc_2-0" class="reference"><a href="value_category.html#cite_note-pmfc-2">[2]</a></sup><span class="t-rev-inl t-until-cxx11"><span>, or where <code>a</code> is an rvalue and <code>m</code> is a non-static data member of non-reference type</span> <span><span class="t-mark-rev t-until-cxx11">(until C++11)</span></span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span>m</span></span>, the built-in <a href="operator_member_access.html#Built-in_member_access_operators" title="cpp/language/operator member access">member of pointer</a> expression, where <code>m</code> is a member enumerator or non-static member function<sup id="cite_ref-pmfc_2-1" class="reference"><a href="value_category.html#cite_note-pmfc-2">[2]</a></sup>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="sy2">*</span>mp</span></span>, the <a href="operator_member_access.html#Built-in_pointer-to-member_access_operators" title="cpp/language/operator member access">pointer to member of object</a> expression, where <code>mp</code> is a pointer to member function<sup id="cite_ref-pmfc_2-2" class="reference"><a href="value_category.html#cite_note-pmfc-2">[2]</a></sup><span class="t-rev-inl t-until-cxx11"><span>, or where <code>a</code> is an rvalue and <code>mp</code> is a pointer to data member</span> <span><span class="t-mark-rev t-until-cxx11">(until C++11)</span></span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span><span class="sy2">*</span>mp</span></span>, the built-in <a href="operator_member_access.html#Built-in_pointer-to-member_access_operators" title="cpp/language/operator member access">pointer to member of pointer</a> expression, where <code>mp</code> is a pointer to member function<sup id="cite_ref-pmfc_2-3" class="reference"><a href="value_category.html#cite_note-pmfc-2">[2]</a></sup>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a, b</span></span>, the built-in <a href="operator_other.html#Built-in_comma_operator" title="cpp/language/operator other">comma</a> expression, where <code>b</code> is an rvalue;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy4">?</span> b <span class="sy4">:</span> c</span></span>, the <a href="operator_other.html#Conditional_operator" title="cpp/language/operator other">ternary conditional</a> expression for some <code>a</code>, <code>b</code>, and <code>c</code>;
</li><li> a cast expression to non-reference type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span><span class="br0">(</span>x<span class="br0">)</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../string/basic_string.html"><span class="kw1072">std::<span class="me2">string</span></span></a><span class="br0">{</span><span class="br0">}</span></span></span>, or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="nu0">42</span></span></span>;
</li></ul>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<ul><li> a <a href="lambda.html" title="cpp/language/lambda">lambda expression</a>, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> x<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> x <span class="sy2">*</span> x<span class="sy4">;</span> <span class="br0">}</span></span></span>.
</li></ul>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr></table>
<p>Properties:
</p>
<ul><li> Same as rvalue (below).
</li><li> A prvalue cannot be <a href="objects.html#Polymorphic_objects" title="cpp/language/object">polymorphic</a>: the <a href="type-id.html#Dynamic_type" title="cpp/language/type">dynamic type</a> of the object it identifies is always the type of the expression.
</li><li> A non-class prvalue cannot be <a href="cv.html" title="cpp/language/cv">cv-qualified</a>.
</li><li> A prvalue cannot have <a href="type-id.html#Incomplete_type" title="cpp/language/type">incomplete type</a> (except for type void, see below, or when used in <a href="decltype.html" title="cpp/language/decltype">decltype specifier</a>).
</li></ul>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<h3> <span class="mw-headline" id="xvalue">xvalue</span></h3>
<p>An <i>xvalue</i> ("expiring value") expression is an expression that <i>has identity</i> and <i>can be moved from</i>.
</p><p>The following expressions are xvalue expressions:
</p>
<ul><li> a function call or overloaded operator expression of rvalue reference to object return type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>x<span class="br0">)</span></span></span>;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>n<span class="br0">]</span></span></span>, the built-in <a href="operator_member_access.html#Built-in_subscript_operator" title="cpp/language/operator member access">subscript</a> expression, where <code>a</code> is an array rvalue;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">m</span></span></span>, the <a href="operator_member_access.html#Built-in_member_access_operators" title="cpp/language/operator member access">member of object</a> expression, where <code>a</code> is an rvalue and <code>m</code> is a non-static data member of non-reference type;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="sy2">*</span>mp</span></span>, the <a href="operator_member_access.html#Built-in_pointer-to-member_access_operators" title="cpp/language/operator member access">pointer to member of object</a> expression, where <code>a</code> is an rvalue and <code>mp</code> is a pointer to data member;
</li><li> <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy4">?</span> b <span class="sy4">:</span> c</span></span>, the <a href="operator_other.html#Conditional_operator" title="cpp/language/operator other">ternary conditional</a> expression for some <code>a</code>, <code>b</code>, and <code>c</code>;
</li><li> a cast expression to rvalue reference to object type, such as <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">char</span><span class="sy3">&&</span><span class="sy1">></span><span class="br0">(</span>x<span class="br0">)</span></span></span>.
</li></ul>
<p>Properties:
</p>
<ul><li> Same as rvalue (below).
</li><li> Same as glvalue (below).
</li></ul>
<p>Like prvalues, xvalues bind to rvalue references, but unlike prvalues, an xvalue may be <a href="objects.html#Polymorphic_objects" title="cpp/language/object">polymorphic</a>, and a non-class xvalue may be <a href="cv.html" title="cpp/language/cv">cv-qualified</a>.
</p>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr>
</table>
<h2><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=5" title="Edit section: Mixed categories">edit</a>]</span> <span class="mw-headline" id="Mixed_categories">Mixed categories</span></h2>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=6" title="Edit section: glvalue">edit</a>]</span> <span class="mw-headline" id="glvalue">glvalue</span></h3>
<p>A <i>glvalue</i> ("generalized lvalue") expression is an expression that is either an lvalue or an xvalue. It <i>has identity</i>. It may or may not be moved from.
</p><p>Properties (note: these apply to pre-C++11 lvalues as well):
</p>
<ul><li> A glvalue may be implicitly converted to prvalue with lvalue-to-rvalue, array-to-pointer, or function-to-pointer <a href="implicit_cast.html" title="cpp/language/implicit cast">implicit conversion</a>.
</li><li> A glvalue may be <a href="objects.html#Polymorphic_objects" title="cpp/language/object">polymorphic</a>: the <a href="type-id.html#Dynamic_type" title="cpp/language/type">dynamic type</a> of the object it identifies is not necessarily the static type of the expression.
</li><li> A glvalue can have <a href="type-id.html#Incomplete_type" title="cpp/language/type">incomplete type</a>, where permitted by the expression.
</li></ul>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=7" title="Edit section: rvalue">edit</a>]</span> <span class="mw-headline" id="rvalue">rvalue</span></h3>
<p>An <i>rvalue</i> ("right value") expression is an expression that is either a prvalue or an xvalue. It <i>can be moved from</i>. It may or may not have identity. The naming is historic and reflects the use of rvalue expressions as the right-hand operand of the assignment operator in the CPL programming language.
</p><p>Properties (note: these apply to pre-C++11 rvalues as well):
</p>
<ul><li> Address of an rvalue may not be taken: <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><span class="kw4">int</span><span class="br0">(</span><span class="br0">)</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span>i<span class="sy2">++</span></span></span><sup id="cite_ref-3" class="reference"><a href="value_category.html#cite_note-3">[3]</a></sup>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><span class="nu0">42</span></span></span>, and <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>val<span class="br0">)</span></span></span> are invalid.
</li><li> An rvalue can't be used as the left-hand operand of the built-in assignment or compound assignment operator.
</li><li> An rvalue may be used to <a href="reference_initialization.html" title="cpp/language/reference initialization">initialize a const lvalue reference</a>, in which case the lifetime of the object identified by the rvalue is extended until the scope of the reference ends.
</li></ul>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<ul><li> An rvalue may be used to <a href="reference_initialization.html" title="cpp/language/reference initialization">initialize an rvalue reference</a>, in which case the lifetime of the object identified by the rvalue is extended until the scope of the reference ends.
</li><li> When used as a function argument and when <a href="overload_resolution.html" title="cpp/language/overload resolution">two overloads</a> of the function are available, one taking rvalue reference parameter and the other taking lvalue reference to const parameter, rvalues bind to the rvalue reference overload (thus, if both copy and move constructors are available, rvalue arguments invoke the <a href="move_constructor.html" title="cpp/language/move constructor">move constructor</a>, and likewise with copy and move assignment operators).
</li></ul>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr>
</table>
<h2><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=8" title="Edit section: Special categories">edit</a>]</span> <span class="mw-headline" id="Special_categories">Special categories</span></h2>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=9" title="Edit section: Pending member function call">edit</a>]</span> <span class="mw-headline" id="Pending_member_function_call">Pending member function call</span></h3>
<p>The expressions <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">mf</span></span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span>mf</span></span>, where <code>mf</code> is a <a href="member_functions.html" title="cpp/language/member functions">non-static member function</a>, and the expressions <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="sy2">*</span>mfp</span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp">p<span class="sy2">-</span><span class="sy1">></span><span class="sy2">*</span>mfp</span></span>, where <code>mfp</code> is a <a href="pointer.html#Pointers_to_member_functions" title="cpp/language/pointer">pointer to member function</a>, are classified as prvalue expressions, but they cannot be used to initialize references, as function arguments, or for any purpose at all, except as the left-hand argument of the function call operator, e.g. <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>p<span class="sy2">-</span><span class="sy1">></span><span class="sy2">*</span>mfp<span class="br0">)</span><span class="br0">(</span>args<span class="br0">)</span></span></span>.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=10" title="Edit section: Void expressions">edit</a>]</span> <span class="mw-headline" id="Void_expressions">Void expressions</span></h3>
<p>Function call expressions returning <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>, cast expressions to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>, and <a href="throw.html" title="cpp/language/throw">throw-expressions</a> are classified as prvalue expressions, but they cannot be used to initialize references or as function arguments. They can be used in some contexts (e.g. on a line of its own, as the left-hand operand of the comma operator, etc) and in the <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span></span></span> statement in a function returning <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>. In addition, throw-expressions may be used as the second and the third operands of the <a href="operator_other.html" title="cpp/language/operator other">conditional operator ?:</a> (other void prvalues can only be used if appearing as both second and third operands).
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=11" title="Edit section: Bit fields">edit</a>]</span> <span class="mw-headline" id="Bit_fields">Bit fields</span></h3>
<p>An expression that designates a <a href="bit_field.html" title="cpp/language/bit field">bit field</a> (e.g. <span class="t-c"><span class="mw-geshi cpp source-cpp">a.<span class="me1">m</span></span></span>, where <code>a</code> is an lvalue of type <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">struct</span> A <span class="br0">{</span> <span class="kw4">int</span> m<span class="sy4">:</span> <span class="nu0">3</span><span class="sy4">;</span> <span class="br0">}</span></span></span>) is an lvalue expression: it may be used as the left-hand operand of the assignment operator, but its address cannot be taken and a non-const lvalue reference cannot be bound to it. A const lvalue reference can be initialized from a bit-field lvalue, but a temporary copy of the bit-field will be made: it won't bind to the bit field directly.
</p>
<h2><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=12" title="Edit section: Footnotes">edit</a>]</span> <span class="mw-headline" id="Footnotes">Footnotes</span></h2>
<ol class="references">
<li id="cite_note-1"><span class="mw-cite-backlink"><a href="value_category.html#cite_ref-1">↑</a></span> <span class="reference-text">Assuming <span class="t-c"><span class="mw-geshi cpp source-cpp">i</span></span> has built-in type or the pre-increment operator is <a href="operators.html" title="cpp/language/operators">overloaded</a> to return by lvalue reference</span>
</li>
<li id="cite_note-pmfc-2"><span class="mw-cite-backlink">↑ <sup><a href="value_category.html#cite_ref-pmfc_2-0">2.0</a></sup> <sup><a href="value_category.html#cite_ref-pmfc_2-1">2.1</a></sup> <sup><a href="value_category.html#cite_ref-pmfc_2-2">2.2</a></sup> <sup><a href="value_category.html#cite_ref-pmfc_2-3">2.3</a></sup></span> <span class="reference-text">special rvalue category, see pending member function call</span>
</li>
<li id="cite_note-3"><span class="mw-cite-backlink"><a href="value_category.html#cite_ref-3">↑</a></span> <span class="reference-text">Assuming <span class="t-c"><span class="mw-geshi cpp source-cpp">i</span></span> has built-in type or the postincrement operator is not <a href="operators.html" title="cpp/language/operators">overloaded</a> to return by lvalue reference</span>
</li>
</ol>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=13" title="Edit section: External references">edit</a>]</span> <span class="mw-headline" id="External_references">External references</span></h3>
<p><a rel="nofollow" class="external text" href="http://www.stroustrup.com/terminology.pdf">"New" Value Terminology</a> by Bjarne Stroustrup, 2010
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=14" title="Edit section: Defect reports">edit</a>]</span> <span class="mw-headline" id="Defect_reports">Defect reports</span></h3>
<p>The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
</p>
<table class="dsctable" style="font-size:0.8em">
<tr>
<th> DR
</th>
<th> Applied to
</th>
<th> Behavior as published
</th>
<th> Correct behavior
</th></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#616">CWG 616</a>
</td>
<td> C++11
</td>
<td> member access and member access through pointer to member of an rvalue resulted in prvalue
</td>
<td> reclassified as xvalue
</td></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1213">CWG 1213</a>
</td>
<td> C++11
</td>
<td> subscripting an array rvalue resulted in lvalue
</td>
<td> reclassified as xvalue
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/value_category&action=edit&section=15" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../../c/language/value_category.html" title="c/language/value category">C documentation</a></span> for <span class="t-dsc-see-tt"><span>value categories</span></span></div>
</td></tr>
</table>
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