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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>tie</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-tuple.html">tuple</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-tuple.html"><tuple></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span>... <span class="me1">Types</span> <span class="sy1">></span><br />
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<a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span>Types<span class="sy3">&</span>...<span class="sy1">></span> tie<span class="br0">(</span> Types<span class="sy3">&</span>... <span class="me1">args</span> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark-rev t-until-cxx14">(C++14 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span>... <span class="me1">Types</span> <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span>Types<span class="sy3">&</span>...<span class="sy1">></span> tie<span class="br0">(</span> Types<span class="sy3">&</span>... <span class="me1">args</span> <span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td>
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<p>创建到其参数或 <span class="t-lc"><a href="cpp-utility-tuple-ignore.html">std::ignore</a></span> 实例的左值引用的 tuple 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>args</td>
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<td>-</td>
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<td>构造 tuple 所用的零或更多左值参数</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>含左值引用的 <span class="t-lc"><a href="cpp-utility-tuple.html">std::tuple</a></span> 对象。</p>
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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">可能的实现</span></h3>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">typename</span>... <span class="me1">Args</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> <span class="co1">// C++14 起</span>
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<a href="cpp-utility-tuple.html"><span class="kw1098">std::<span class="me2">tuple</span></span></a><span class="sy1"><</span>Args<span class="sy3">&</span>...<span class="sy1">></span> tie<span class="br0">(</span>Args<span class="sy3">&</span>... <span class="me1">args</span><span class="br0">)</span> <span class="kw1">noexcept</span> <span class="br0">{</span>
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<span class="kw1">return</span> <span class="br0">{</span>args...<span class="br0">}</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p><code>std::tie</code> 可用于解包 <span class="t-lc"><a href="cpp-utility-pair.html">std::pair</a></span> ，因为 <span class="t-lc"><a href="cpp-utility-tuple.html">std::tuple</a></span> 拥有从 pair 的<a href="cpp-utility-tuple-operator=.html">转换赋值</a>：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw4">bool</span> result<span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">tie</span><span class="br0">(</span><a href="cpp-utility-tuple-ignore.html"><span class="kw1115">std::<span class="me2">ignore</span></span></a>, result<span class="br0">)</span> <span class="sy1">=</span> set.<span class="me1">insert</span><span class="br0">(</span>value<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">示例</span></h3>
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<div class="t-example">
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<p><code>std::tie</code> 能用于引入字典序比较到结构体，或解包 tuple ：</p>
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <set></span>
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<span class="co2">#include <tuple></span>
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<span class="kw1">struct</span> S <span class="br0">{</span>
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<span class="kw4">int</span> n<span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a> s<span class="sy4">;</span>
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<span class="kw4">float</span> d<span class="sy4">;</span>
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<span class="kw4">bool</span> operator<span class="sy1"><</span><span class="br0">(</span><span class="kw4">const</span> S<span class="sy3">&</span> rhs<span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<span class="co1">// 比较 n 与 rhs.n,</span>
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<span class="co1">// 然后为 s 与 rhs.s,</span>
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<span class="co1">// 然后为 d 与 rhs.d</span>
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<span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">tie</span><span class="br0">(</span>n, s, d<span class="br0">)</span> <span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">tie</span><span class="br0">(</span>rhs.<span class="me1">n</span>, rhs.<span class="me1">s</span>, rhs.<span class="me1">d</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-container-set.html"><span class="kw1276">std::<span class="me2">set</span></span></a><span class="sy1"><</span>S<span class="sy1">></span> set_of_s<span class="sy4">;</span> <span class="co1">// S 为可比较小于 (LessThanComparable)</span>
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S value<span class="br0">{</span><span class="nu0">42</span>, <span class="st0">"Test"</span>, <span class="nu16">3.14</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-set.html"><span class="kw1276">std::<span class="me2">set</span></span></a><span class="sy1"><</span>S<span class="sy1">></span><span class="sy4">::</span><span class="me2">iterator</span> iter<span class="sy4">;</span>
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<span class="kw4">bool</span> inserted<span class="sy4">;</span>
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<span class="co1">// 解包 insert 的返回值为 iter 与 inserted</span>
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std<span class="sy4">::</span><span class="me2">tie</span><span class="br0">(</span>iter, inserted<span class="br0">)</span> <span class="sy1">=</span> set_of_s.<span class="me1">insert</span><span class="br0">(</span>value<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>inserted<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Value was inserted successfully<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">Value was inserted successfully</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td><a href="cpp-language-structured_binding.html">结构化绑定</a> <span class="t-mark-rev t-since-cxx17">(C++17)</span></td>
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<td>绑定指定的名字到初始化器的子对象或元组元素</td>
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<tr class="t-dsc">
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<div><a href="cpp-utility-tuple-make_tuple.html"><span class="t-lines"><span>make_tuple</span></span></a></div>
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<td>创建一个 <code>tuple</code> 对象，其类型根据各实参类型定义<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-tuple-forward_as_tuple.html"><span class="t-lines"><span>forward_as_tuple</span></span></a></div>
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</div>
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<td>创建<a href="cpp-language-reference.html#.E8.BD.AC.E5.8F.91.E5.BC.95.E7.94.A8">转发引用</a>的 <code>tuple</code><br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="cpp-utility-tuple-tuple_cat.html"><span class="t-lines"><span>tuple_cat</span></span></a></div>
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</div>
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</td>
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<td>通过连接任意数量的元组来创建一个<code>tuple</code><br />
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<span class="t-mark">(函数模板)</span></td>
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<div><a href="cpp-utility-tuple-ignore.html"><span class="t-lines"><span>ignore</span></span></a></div>
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</td>
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<td>用 <strong class="selflink"><tt>tie</tt></strong> 解包 <code>tuple</code> 时用来跳过元素的占位符<br />
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<span class="t-mark">(常量)</span></td>
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