147 lines
8.4 KiB
HTML
147 lines
8.4 KiB
HTML
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<title>std::tuple_size(std::array)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_array_tuple_size skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>tuple_size<small>(std::array)</small></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-container.html">container</a>‎ | <a href="cpp-container-array.html">array</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-array.html"><array></a></code></div>
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<td></td>
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<tr class="t-dcl t-since-cxx11">
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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> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></span>
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<p><span class="kw1">struct</span> tuple_size<span class="sy1"><</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>T, N<span class="sy1">></span> <span class="sy1">></span> <span class="sy4">:</span><br />
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<a href="cpp-types-integral_constant.html"><span class="kw647">std::<span class="me2">integral_constant</span></span></a><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a>, N<span class="sy1">></span><br /></p>
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<span class="br0">{</span> <span class="br0">}</span><span class="sy4">;</span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<td></td>
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<p>提供作为编译时常量表达式访问 <span class="t-lc"><a href="cpp-container-array.html">std::array</a></span> 中元素数量的方法。</p>
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<div class="t-inherited">
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<h2><span class="mw-headline" id=".E7.BB.A7.E6.89.BF.E8.87.AA_std::integral_constant">继承自 <a href="cpp-types-integral_constant.html"><span style="font-size:0.7em; line-height:130%">std::</span>integral_constant</a></span></h2>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.B8.B8.E9.87.8F">成员常量</span></h3>
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<div><span class="t-lines"><span>value</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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<td><code>N</code> ， array 中的元素数<br />
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<span class="t-mark">(公开静态成员常量)</span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div><span class="t-lines"><span>operator std::size_t</span></span></div>
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<td>转换对象为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a></span></span> ，返回 <code>value</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>operator()</span></span></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
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<td>返回 <code>value</code><br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>类型</td>
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<td>定义</td>
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<td><code>value_type</code></td>
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<td><code>std::size_t</code></td>
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<td><code>type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-integral_constant.html"><span class="kw647">std::<span class="me2">integral_constant</span></span></a><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a>, value<span class="sy1">></span></span></span></td>
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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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<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 <array></span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span>
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<span class="kw4">void</span> test<span class="br0">(</span>T t<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> a<span class="br0">[</span><a href="cpp-utility-tuple-tuple_size.html"><span class="kw1101">std::<span class="me2">tuple_size</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 能用于编译时</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-utility-tuple-tuple_size.html"><span class="kw1101">std::<span class="me2">tuple_size</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">value</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</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-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">float</span>, <span class="nu0">3</span><span class="sy1">></span> arr<span class="sy4">;</span>
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test<span class="br0">(</span>arr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</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">3</pre></div>
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</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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<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 class="t-dsc-member-div">
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<div><a href="cpp-utility-tuple-tuple_size.html"><span class="t-lines"><span>std::tuple_size<span class="t-dsc-small"><std::tuple></span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>在编译时获得 <code>tuple</code> 的大小<br />
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<span class="t-mark">(类模板特化)</span></td>
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</div>
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<div class="visualClear"></div>
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