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<title>std::tuple_element&lt;std::tuple&gt;</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>tuple_element<small>&lt;std::tuple&gt;</small></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>&lrm; | <a href="cpp-utility-tuple.html">tuple</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-tuple.html">&lt;tuple&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> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span>... <span class="me1">Types</span> <span class="sy1">&gt;</span><br />
<span class="kw1">class</span> tuple_element<span class="sy1">&lt;</span> I, tuple<span class="sy1">&lt;</span>Types...<span class="sy1">&gt;</span> <span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<p>&#25552;&#20379; tuple &#20803;&#32032;&#31867;&#22411;&#30340;&#32534;&#35793;&#26102;&#24102;&#19979;&#26631;&#35775;&#38382;&#12290;</p>
<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">&#25104;&#21592;&#31867;&#22411;</span></h3>
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<td>type</td>
<td>tuple &#30340;&#31532; <code>I</code> &#20803;&#32032;&#30340;&#31867;&#22411;&#65292;&#20854;&#20013; <code>I</code> &#22312; <code>[0, sizeof...(Types))</code> &#20013;</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> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> T <span class="sy1">&gt;</span>
<span class="kw1">struct</span> tuple_element<span class="sy4">;</span>
<span class="co1">// &#36882;&#24402;&#24773;&#20917;</span>
<span class="kw1">template</span><span class="sy1">&lt;</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> Head, <span class="kw1">class</span>... <span class="me1">Tail</span> <span class="sy1">&gt;</span>
<span class="kw1">struct</span> tuple_element<span class="sy1">&lt;</span>I, <a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1">&lt;</span>Head, Tail...<span class="sy1">&gt;&gt;</span>
<span class="sy4">:</span> std<span class="sy4">::</span><span class="me2">tuple_element</span><span class="sy1">&lt;</span>I<span class="sy2">-</span><span class="nu0">1</span>, <a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1">&lt;</span>Tail...<span class="sy1">&gt;&gt;</span> <span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="co1">// &#22522;&#30784;&#24773;&#20917;</span>
<span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> Head, <span class="kw1">class</span>... <span class="me1">Tail</span> <span class="sy1">&gt;</span>
<span class="kw1">struct</span> tuple_element<span class="sy1">&lt;</span><span class="nu0">0</span>, <a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1">&lt;</span>Head, Tail...<span class="sy1">&gt;&gt;</span> <span class="br0">{</span>
<span class="kw1">using</span> type <span class="sy1">=</span> Head<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span></pre></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<div class="t-example">
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<pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;tuple&gt;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span>... <span class="me1">Args</span><span class="sy1">&gt;</span>
<span class="kw1">struct</span> type_list
<span class="br0">{</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span>
<span class="kw1">using</span> type <span class="sy1">=</span> <span class="kw1">typename</span> std<span class="sy4">::</span><span class="me2">tuple_element</span><span class="sy1">&lt;</span>N, <a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1">&lt;</span>Args...<span class="sy1">&gt;&gt;</span><span class="sy4">::</span><span class="me2">type</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1762">std::<span class="me2">boolalpha</span></span></a><span class="sy4">;</span>
type_list<span class="sy1">&lt;</span><span class="kw4">int</span>, <span class="kw4">char</span>, <span class="kw4">bool</span><span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">type</span><span class="sy1">&lt;</span><span class="nu0">2</span><span class="sy1">&gt;</span> x <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> x <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">true</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<td><a href="cpp-language-structured_binding.html">&#32467;&#26500;&#21270;&#32465;&#23450;</a> <span class="t-mark-rev t-since-cxx17">(C++17)</span></td>
<td>&#32465;&#23450;&#25351;&#23450;&#30340;&#21517;&#23383;&#21040;&#21021;&#22987;&#21270;&#22120;&#30340;&#23376;&#23545;&#35937;&#25110;&#20803;&#32452;&#20803;&#32032;</td>
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<div><a href="cpp-utility-tuple_size.html"><span class="t-lines"><span>tuple_size</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>&#33719;&#24471;&#20803;&#32452;&#24335;&#31867;&#22411;&#30340;&#20803;&#32032;&#25968;<br />
<span class="t-mark">(&#31867;&#27169;&#26495;)</span></td>
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<div><a href="cpp-utility-tuple-get.html"><span class="t-lines"><span>std::get<span class="t-dsc-small">(std::tuple)</span></span></span></a></div>
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<td>&#20803;&#32452;&#24335;&#35775;&#38382;&#25351;&#23450;&#30340;&#20803;&#32032;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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