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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>exchange</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-utility.html">utility</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-utility.html">&lt;utility&gt;</a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">=</span> T <span class="sy1">&gt;</span><br />
T exchange<span class="br0">(</span> T<span class="sy3">&amp;</span> obj, U<span class="sy3">&amp;&amp;</span> new_value <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx14">(C++14 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">=</span> T <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> T exchange<span class="br0">(</span> T<span class="sy3">&amp;</span> obj, U<span class="sy3">&amp;&amp;</span> new_value <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx23">(C++23 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">=</span> T <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> T exchange<span class="br0">(</span> T<span class="sy3">&amp;</span> obj, U<span class="sy3">&amp;&amp;</span> new_value <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 &#36215;)</span></td>
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<p>&#20197; <code>new_value</code> &#26367;&#25442; <code>obj</code> &#30340;&#20540;&#65292;&#24182;&#36820;&#22238; <code>obj</code> &#30340;&#26087;&#20540;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<table class="t-par-begin">
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<td>obj</td>
<td>-</td>
<td>&#35201;&#26367;&#25442;&#20540;&#30340;&#23545;&#35937;</td>
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<td>new_value</td>
<td>-</td>
<td>&#35201;&#36171;&#32473; <code>obj</code> &#30340;&#20540;</td>
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<td colspan="3">&#31867;&#22411;&#35201;&#27714;</td>
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<td colspan="3">-
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<code>T</code> &#24517;&#39035;&#28385;&#36275;<a href="cpp-named_req-MoveConstructible.html"><span style="font-style:italic">&#21487;&#31227;&#21160;&#26500;&#36896;</span> <span style="font-family: Georgia, &#39;DejaVu Serif&#39;, serif; font-style:italic">(MoveConstructible)</span></a> &#30340;&#35201;&#27714;&#12290;&#32780;&#19988;&#24517;&#39035;&#33021;&#31227;&#21160;&#36171;&#20540; <code>U</code> &#31867;&#22411;&#23545;&#35937;&#32473; <code>T</code> &#31867;&#22411;&#23545;&#35937;</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p><code>obj</code> &#30340;&#26087;&#20540;</p>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
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<p>&#65288;&#26080;&#65289;</p>
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<td><span class="t-mark-rev t-until-cxx23">(C++23 &#21069;)</span></td>
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<div class="t-noexcept-full"><a href="cpp-language-noexcept_spec.html"><tt>noexcept</tt></a> &#35828;&#26126;&#65306;&nbsp;&nbsp;
<div class="t-noexcept-box"><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span><br /></span></span>
<p>&nbsp; &nbsp; <a href="cpp-types-is_move_constructible.html"><span class="kw543">std::<span class="me2">is_nothrow_move_constructible_v</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span><br />
&nbsp; &nbsp; <a href="cpp-types-is_assignable.html"><span class="kw549">std::<span class="me2">is_nothrow_assignable_v</span></span></a><span class="sy1">&lt;</span>T<span class="sy3">&amp;</span>, U<span class="sy1">&gt;</span><br /></p>
<span class="br0">)</span></div>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 &#36215;)</span></td>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">&#21487;&#33021;&#30340;&#23454;&#29616;</span></h3>
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<pre class="de1"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">=</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="co1">// C++20 &#36215;</span>
T exchange<span class="br0">(</span>T<span class="sy3">&amp;</span> obj, U<span class="sy3">&amp;&amp;</span> new_value<span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span>
<a href="cpp-types-is_move_constructible.html"><span class="kw542">std::<span class="me2">is_nothrow_move_constructible</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">value</span> <span class="sy3">&amp;&amp;</span> <a href="cpp-types-is_assignable.html"><span class="kw548">std::<span class="me2">is_nothrow_assignable</span></span></a><span class="sy1">&lt;</span>T<span class="sy3">&amp;</span>, U<span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">value</span>
<span class="br0">)</span>
<span class="br0">{</span>
T old_value <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>obj<span class="br0">)</span><span class="sy4">;</span>
obj <span class="sy1">=</span> <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span><span class="br0">(</span>new_value<span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">return</span> old_value<span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#33021;&#22312;&#23454;&#29616;<a href="cpp-language-move_assignment.html">&#31227;&#21160;&#36171;&#20540;&#36816;&#31639;&#31526;</a>&#21644;<a href="cpp-language-move_constructor.html">&#31227;&#21160;&#26500;&#36896;&#20989;&#25968;</a>&#26102;&#20351;&#29992;&#27492;&#20989;&#25968;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">struct</span> S
<span class="br0">{</span>
<span class="kw4">int</span> n<span class="sy4">;</span>
S<span class="br0">(</span>S<span class="sy3">&amp;&amp;</span> other<span class="br0">)</span> <span class="kw1">noexcept</span> <span class="sy4">:</span> n<span class="br0">{</span>std<span class="sy4">::</span><span class="me2">exchange</span><span class="br0">(</span>other.<span class="me1">n</span>, <span class="nu0">0</span><span class="br0">)</span><span class="br0">}</span>
<span class="br0">{</span><span class="br0">}</span>
S<span class="sy3">&amp;</span> operator<span class="sy1">=</span><span class="br0">(</span>S<span class="sy3">&amp;&amp;</span> other<span class="br0">)</span> <span class="kw1">noexcept</span>
<span class="br0">{</span>
<span class="kw1">if</span><span class="br0">(</span>this <span class="sy3">!</span><span class="sy1">=</span> <span class="sy3">&amp;</span>other<span class="br0">)</span>
n <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">exchange</span><span class="br0">(</span>other.<span class="me1">n</span>, <span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// &#31227;&#21160; n &#65292;&#24182;&#20110; other.n &#30041;&#19979;&#38646;</span>
<span class="kw1">return</span> <span class="sy2">*</span>this<span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div>
</div>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<div class="t-example">
<div class="t-example-live-link"></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;utility&gt;</span>
<span class="co2">#include &lt;vector&gt;</span>
<span class="co2">#include &lt;iterator&gt;</span>
<span class="kw1">class</span> stream
<span class="br0">{</span>
<span class="kw1">public</span><span class="sy4">:</span>
<span class="kw1">using</span> flags_type <span class="sy1">=</span> <span class="kw4">int</span><span class="sy4">;</span>
<span class="kw1">public</span><span class="sy4">:</span>
flags_type flags<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span>
<span class="br0">{</span> <span class="kw1">return</span> flags_<span class="sy4">;</span> <span class="br0">}</span>
<span class="co1">/// &#20197; newf &#26367;&#25442; flags_ &#24182;&#36820;&#22238;&#26087;&#20540;&#12290;</span>
flags_type flags<span class="br0">(</span>flags_type newf<span class="br0">)</span>
<span class="br0">{</span> <span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">exchange</span><span class="br0">(</span>flags_, newf<span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="kw1">private</span><span class="sy4">:</span>
flags_type flags_ <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;f()&quot;</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
stream s<span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s.<span class="me1">flags</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s.<span class="me1">flags</span><span class="br0">(</span><span class="nu0">12</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s.<span class="me1">flags</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span><span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<a href="cpp-container-vector.html"><span class="kw1268">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> v<span class="sy4">;</span>
<span class="co1">// &#22240;&#20026;&#31532;&#20108;&#27169;&#26495;&#24418;&#21442;&#26377;&#40664;&#35748;&#20540;&#65292;&#25925;&#33021;&#20197;&#33457;&#25324;&#21495;&#21021;&#22987;&#21270;&#21015;&#22120;&#34920;&#20026;&#31532;&#20108;&#21442;&#25968;&#12290;</span>
<span class="co1">// &#19979;&#26041;&#34920;&#36798;&#24335;&#31561;&#20215;&#20110; std::exchange(v, std::vector&lt;int&gt;{1,2,3,4});</span>
std<span class="sy4">::</span><span class="me2">exchange</span><span class="br0">(</span>v, <span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-algorithm-copy.html"><span class="kw1581">std::<span class="me2">copy</span></span></a><span class="br0">(</span>begin<span class="br0">(</span>v<span class="br0">)</span>,end<span class="br0">(</span>v<span class="br0">)</span>, <a href="cpp-iterator-ostream_iterator.html"><span class="kw670">std::<span class="me2">ostream_iterator</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">(</span><a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a>,<span class="st0">&quot;, &quot;</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span><span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="kw4">void</span> <span class="br0">(</span><span class="sy2">*</span>fun<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// &#27169;&#26495;&#24418;&#21442;&#30340;&#40664;&#35748;&#20540;&#20134;&#20351;&#24471;&#33021;&#20197;&#36890;&#24120;&#20989;&#25968;&#20026;&#31532;&#20108;&#21442;&#25968;&#12290;</span>
<span class="co1">// &#19979;&#26041;&#34920;&#36798;&#24335;&#31561;&#20215;&#20110; std::exchange(fun, static_cast&lt;void(*)()&gt;(f))</span>
std<span class="sy4">::</span><span class="me2">exchange</span><span class="br0">(</span>fun,f<span class="br0">)</span><span class="sy4">;</span>
fun<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
<p>&#36755;&#20986;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="text source-text">
<pre class="de1">0
0
12
1, 2, 3, 4,
f()</pre></div>
</div>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
<div><a href="cpp-algorithm-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
</div>
</td>
<td>&#20132;&#25442;&#20004;&#20010;&#23545;&#35937;&#30340;&#20540;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="cpp-atomic-atomic_exchange.html"><span class="t-lines"><span>atomic_exchange</span><span>atomic_exchange_explicit</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
</div>
</td>
<td>&#21407;&#23376;&#22320;&#20197;&#38750;&#21407;&#23376;&#23454;&#21442;&#30340;&#20540;&#26367;&#25442;&#21407;&#23376;&#23545;&#35937;&#30340;&#20540;&#65292;&#24182;&#36820;&#22238;&#35813;&#21407;&#23376;&#23545;&#35937;&#30340;&#26087;&#20540;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
</tr>
</table>
</div>
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