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<tr class="t-nv"><td colspan="5"> <a href="nullptr.html" title="cpp/language/nullptr"> nullptr</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="user_literal.html" title="cpp/language/user literal"> user-defined</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="type_alias.html" title="cpp/language/type alias"> type alias declaration</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
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<tr class="t-nv"><td colspan="5"> <a href="override.html" title="cpp/language/override"> override specifier</a>  <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="final.html" title="cpp/language/final"> final specifier</a>  <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="explicit.html" title="cpp/language/explicit"> explicit</a>  <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv-h2"><td colspan="5"> Special member functions</td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="default_constructor.html" title="cpp/language/default constructor"> default constructor</a></td></tr>
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<tr class="t-nv-h1"><td colspan="5"> Miscellaneous </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="asm.html" title="cpp/language/asm"> Inline assembly</a></td></tr>
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</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/navbar_content&amp;action=edit">&#91;edit&#93;</a></span></div></div></div></div><div class="t-navbar-sep">&#160;</div></div>
<p>Declares a named variable as a reference, that is, an alias to an already-existing object or function.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a>
<ul>
<li class="toclevel-2 tocsection-2"><a href="#Lvalue_references"><span class="tocnumber">1.1</span> <span class="toctext">Lvalue references</span></a></li>
<li class="toclevel-2 tocsection-3"><a href="#Rvalue_references"><span class="tocnumber">1.2</span> <span class="toctext">Rvalue references</span></a></li>
<li class="toclevel-2 tocsection-4"><a href="#Dangling_references"><span class="tocnumber">1.3</span> <span class="toctext">Dangling references</span></a></li>
</ul>
</li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/reference&amp;action=edit&amp;section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
<p>A reference variable declaration is any simple declaration whose <a href="declarations" title="cpp/language/declarations">declarator</a> has the form
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>&amp;</b></code> <span class="t-spar">attr</span><span class="t-mark">(optional)</span> <span class="t-spar">declarator</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> <code><b>&amp;&amp;</b></code> <span class="t-spar">attr</span><span class="t-mark">(optional)</span> <span class="t-spar">declarator</span>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<div class="t-li1"><span class="t-li">1)</span> <b>Lvalue reference declarator</b>: the declaration <span class="t-c"><span class="mw-geshi cpp source-cpp">S <span class="sy3">&amp;</span> D<span class="sy4">;</span></span></span> declares <code>D</code> as an <i>lvalue reference</i> to the type determined by <span class="t-spar">decl-specifier-seq</span> <code>S</code>.</div>
<div class="t-li1"><span class="t-li">2)</span> <b>Rvalue reference declarator</b>: the declaration <span class="t-c"><span class="mw-geshi cpp source-cpp">S <span class="sy3">&amp;&amp;</span> D<span class="sy4">;</span></span></span> declares <code>D</code> as an <i>rvalue reference</i> to type determined by <span class="t-spar">decl-specifier-seq</span> <code>S</code>.</div>
<table class="t-par-begin">


<tr class="t-par">
<td>  <span class="t-spar">declarator</span>
</td>
<td> -
</td>
<td>  any <a href="declarations" title="cpp/language/declarations">declarator</a> except another reference declarator (there are no references to references)
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">attr</span><span class="t-mark-rev t-since-cxx11">(C++11)</span>
</td>
<td> -
</td>
<td>  optional list of <a href="attributes.html" title="cpp/language/attributes">attributes</a>
</td></tr></table>
<p>A declaration of a reference (except for class members and function parameters) is required to contain an initializer: see <a href="reference_initialization.html" title="cpp/language/reference initialization">reference initialization</a> which must identify a valid object or function.
</p><p>There are no references to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> and no references to references.
</p><p>Reference types cannot be <a href="cv.html" title="cpp/language/cv">cv-qualified</a> at the top level; there is no syntax for that in declaration, and if a qualification is introduced through a typedef, it is ignored.
</p><p>References are not objects; they do not necessarily occupy storage, although the compiler may allocate storage if it is necessary to implement the desired semantics (e.g. a non-static data member of reference type usually increases the size of the class by the amount necessary to store a memory address)
</p><p>Because references are not objects, there are no arrays of references, no pointers to references, and no references to references:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">int</span><span class="sy3">&amp;</span> a<span class="br0">&#91;</span><span class="nu0">3</span><span class="br0">&#93;</span><span class="sy4">;</span> <span class="co1">// error</span>
<span class="kw4">int</span><span class="sy3">&amp;</span><span class="sy2">*</span> p<span class="sy4">;</span> <span class="co1">// error</span>
<span class="kw4">int</span><span class="sy3">&amp;</span> <span class="sy3">&amp;</span>r<span class="sy4">;</span> <span class="co1">// error</span></pre></div></div>
<p>However, it is permitted to form references to references through type manipulations in templates or typedefs, in which case the <i>reference collapsing</i> rules apply: rvalue reference to rvalue reference collapses to rvalue reference, all other combinations form lvalue reference:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">typedef</span> <span class="kw4">int</span><span class="sy3">&amp;</span>  lref<span class="sy4">;</span>
<span class="kw1">typedef</span> <span class="kw4">int</span><span class="sy3">&amp;&amp;</span> rref<span class="sy4">;</span>
<span class="kw4">int</span> n<span class="sy4">;</span>
lref<span class="sy3">&amp;</span>  r1 <span class="sy1">=</span> n<span class="sy4">;</span> <span class="co1">// type of r1 is int&amp;</span>
lref<span class="sy3">&amp;&amp;</span> r2 <span class="sy1">=</span> n<span class="sy4">;</span> <span class="co1">// type of r2 is int&amp;</span>
rref<span class="sy3">&amp;</span>  r3 <span class="sy1">=</span> n<span class="sy4">;</span> <span class="co1">// type of r3 is int&amp;</span>
rref<span class="sy3">&amp;&amp;</span> r4 <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// type of r4 is int&amp;&amp;</span></pre></div></div>
<p>(this is part of the rules that make <span class="t-lc"><a href="../utility/forward.html" title="cpp/utility/forward">std::forward</a></span> possible)
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/reference&amp;action=edit&amp;section=2" title="Edit section: Lvalue references">edit</a>]</span> <span class="mw-headline" id="Lvalue_references">Lvalue references</span></h4>
<p>Lvalue references can be used to alias an existing object (optionally with different cv-qualification)
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw4">int</span> main<span class="br0">&#40;</span><span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> s <span class="sy1">=</span> <span class="st0">&quot;Ex&quot;</span><span class="sy4">;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> r1 <span class="sy1">=</span> s<span class="sy4">;</span>
    <span class="kw4">const</span> <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> r2 <span class="sy1">=</span> s<span class="sy4">;</span>
&#160;
    r1 <span class="sy2">+</span><span class="sy1">=</span> <span class="st0">&quot;ample&quot;</span><span class="sy4">;</span> <span class="co1">// modifies s</span>
<span class="co1">//  r2 += &quot;!&quot;; // error: cannot modify through reference to const</span>
    <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> r2 <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span> <span class="co1">// prints s, which now holds &quot;Example&quot;</span>
<span class="br0">&#125;</span></pre></div></div>
<p><br /> 
</p>
</div>
<p>They can also be used to implement pass-by-reference semantics in function calls:
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw4">void</span> double_string<span class="br0">&#40;</span><a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> s<span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    s <span class="sy2">+</span><span class="sy1">=</span> s<span class="sy4">;</span> <span class="co1">// 's' is the same object as main()'s 'str'</span>
<span class="br0">&#125;</span>
<span class="kw4">int</span> main<span class="br0">&#40;</span><span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> <span class="st0">&quot;Test&quot;</span><span class="sy4">;</span>
    double_string<span class="br0">&#40;</span>str<span class="br0">&#41;</span><span class="sy4">;</span>
    <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> str <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">&#125;</span></pre></div></div>
<p><br /> 
</p>
</div>
<p>When a function's return type is lvalue reference, the function call expression becomes an <a href="value_category.html" title="cpp/language/value category">lvalue expression</a>:
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw4">char</span><span class="sy3">&amp;</span> char_number<span class="br0">&#40;</span><a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> s, <a href="../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n<span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    <span class="kw1">return</span> s.<span class="me1">at</span><span class="br0">&#40;</span>n<span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// string::at() returns a reference to char</span>
<span class="br0">&#125;</span>
<span class="kw4">int</span> main<span class="br0">&#40;</span><span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> <span class="st0">&quot;Test&quot;</span><span class="sy4">;</span>
    char_number<span class="br0">&#40;</span>str, <span class="nu0">1</span><span class="br0">&#41;</span> <span class="sy1">=</span> <span class="st0">'a'</span><span class="sy4">;</span> <span class="co1">// the function call is lvalue, can be assigned to</span>
    <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> str <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">&#125;</span></pre></div></div>
<p><br /> 
</p>
</div>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/reference&amp;action=edit&amp;section=3" title="Edit section: Rvalue references">edit</a>]</span> <span class="mw-headline" id="Rvalue_references">Rvalue references</span></h4>
<p>Rvalue references can be used to extend the lifetime of a modifiable temporary (note, lvalue references to const can <a href="reference_initialization.html" title="cpp/language/reference initialization">extend lifetimes</a> too, but they are not modifiable)
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw4">int</span> main<span class="br0">&#40;</span><span class="br0">&#41;</span>
<span class="br0">&#123;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> s1 <span class="sy1">=</span> <span class="st0">&quot;Test&quot;</span><span class="sy4">;</span>
<span class="co1">//    std::string&amp;&amp; r1 = s1; // error: can't bind to lvalue</span>
&#160;
    <span class="kw4">const</span> <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> r2 <span class="sy1">=</span> s1 <span class="sy2">+</span> s1<span class="sy4">;</span> <span class="co1">// OK, lvalue ref to const extends lifetime</span>
<span class="co1">//    r2 += &quot;Test&quot;; // error: can't modify through reference to const</span>
&#160;
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;&amp;</span> r3 <span class="sy1">=</span> s1 <span class="sy2">+</span> s1<span class="sy4">;</span> <span class="co1">// OK, rvalue ref extends lifetime</span>
    r3 <span class="sy2">+</span><span class="sy1">=</span> <span class="st0">&quot;Test&quot;</span><span class="sy4">;</span> <span class="co1">// this rvalue can be modified</span>
    <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> r3 <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">&#125;</span></pre></div></div>
<p><br /> 
</p>
</div>
<p>More importantly, when a function has both rvalue reference and lvalue reference overloads, the rvalue reference overload binds to rvalues, while the lvalue reference overload binds to lvalues.
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">void</span> f<span class="br0">&#40;</span><span class="kw4">int</span><span class="sy3">&amp;</span> x<span class="br0">&#41;</span>
<span class="br0">&#123;</span>
     <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;lvalue reference overload f(&quot;</span> <span class="sy1">&lt;&lt;</span> x <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;)<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">&#125;</span>
<span class="kw4">void</span> f<span class="br0">&#40;</span><span class="kw4">const</span> <span class="kw4">int</span><span class="sy3">&amp;</span> x<span class="br0">&#41;</span>
<span class="br0">&#123;</span>
     <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;lvalue reference to const overload f(&quot;</span> <span class="sy1">&lt;&lt;</span> x <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;)<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">&#125;</span>
<span class="kw4">void</span> f<span class="br0">&#40;</span><span class="kw4">int</span><span class="sy3">&amp;&amp;</span> x<span class="br0">&#41;</span>
<span class="br0">&#123;</span>
     <a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;rvalue reference overload f(&quot;</span> <span class="sy1">&lt;&lt;</span> x <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;)<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">&#125;</span>
<span class="kw4">int</span> main<span class="br0">&#40;</span><span class="br0">&#41;</span>
<span class="br0">&#123;</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">int</span> x <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span>
    f<span class="br0">&#40;</span>n<span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// calls f(int&amp;)</span>
    f<span class="br0">&#40;</span>x<span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// calls f(const int&amp;)</span>
    f<span class="br0">&#40;</span><span class="nu0">3</span><span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// calls f(int&amp;&amp;)</span>
          <span class="co1">// would call f(const int&amp;) if f(int&amp;&amp;) overload wasn't provided</span>
<span class="br0">&#125;</span></pre></div></div>
<p><br /> 
</p>
</div>
<p>This allows <a href="move_constructor.html" title="cpp/language/move constructor">move constructors</a>, <a href="move_operator.html" title="cpp/language/move operator">move assignment</a> operators, and other move-aware functions (e.g. <a href="../container/vector/push_back.html" title="cpp/container/vector/push back"><tt>vector::push_back()</tt></a> to be automatically selected when suitable.
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/language/reference&amp;action=edit&amp;section=4" title="Edit section: Dangling references">edit</a>]</span> <span class="mw-headline" id="Dangling_references">Dangling references</span></h4>
<p>Although references, once initialized, always refer to valid objects or functions, it is possible to create a program where the life time of the referred-to object ends, but the reference remains accessible (<i>dangling</i>). Accessing such reference is undefined behavior.
A common example a function returning a reference to an automatic variable:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> f<span class="br0">&#40;</span><span class="br0">&#41;</span> <span class="br0">&#123;</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> <span class="st0">&quot;Example&quot;</span><span class="sy4">;</span>
    <span class="kw1">return</span> str<span class="sy4">;</span> <span class="co1">// exits the scope of str: str's destructor is called</span>
<span class="br0">&#125;</span>               <span class="co1">// stack storage deallocated</span>
...
<a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> r <span class="sy1">=</span> f<span class="br0">&#40;</span><span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// r is a dangling reference</span>
<a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> r<span class="sy4">;</span>      <span class="co1">// Undefined: reads from a dangling reference</span>
<a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> s <span class="sy1">=</span> f<span class="br0">&#40;</span><span class="br0">&#41;</span><span class="sy4">;</span> <span class="co1">// Undefined: uses a dangling reference to copy-initialize s</span></pre></div></div>
<p>Note that rvalue references and lvalue references to const extend the lifetimes of temporary objects, see <a href="reference_initialization.html" title="cpp/language/reference initialization">reference_initialization</a> for rules and exceptions.
</p><p>If the referred-to object was destroyed (e.g. by explicit destructor call), but the storage was not deallocated, the following uses of the reference are undefined:
</p>
<div class="t-li1"><span class="t-li">1)</span> lvalue to rvalue conversion (e.g. function call to a function that takes a value)</div>
<div class="t-li1"><span class="t-li">2)</span> access to a non-static data member or a call to a non-static member function</div>
<div class="t-li1"><span class="t-li">3)</span> implicit conversion to a reference to a base class subobject</div>
<div class="t-li1"><span class="t-li">4)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span></span></span> to anything other than <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span><span class="sy3">&amp;</span></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy3">&amp;</span></span></span></div>
<div class="t-li1"><span class="t-li">5)</span> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">dynamic_cast</span></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">typeid</span></span></span> expressions</div>
<p>If an object is recreated at the same memory location (e.g. by placement new), the reference becomes valid once again, if all of the following is true:
</p>
<div class="t-li1"><span class="t-li">1)</span> the storage occupied by the new object exactly overlays the storage occupied by the old object</div>
<div class="t-li1"><span class="t-li">2)</span> the new object has the same type as the old object, ignoring top-level cv-qualifiers</div>
<div class="t-li1"><span class="t-li">3)</span> the original object's type was not const-qualified</div>
<div class="t-li1"><span class="t-li">4)</span> the original object was not a class with const or reference non-static data members</div>
<div class="t-li1"><span class="t-li">5)</span> both the original and the new objects are the most-derived objects of their type</div>
<p>Note, the above rules apply to pointers as well (except that pointers to storage without an object can be additionally cast to <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span>)
</p>
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