90 lines
6.5 KiB
HTML
90 lines
6.5 KiB
HTML
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::shared_ptr<T>::operator[]</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_shared_ptr_operator_at skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::shared_ptr<T>::</span>operator[]</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-memory.html">memory</a>‎ | <a href="cpp-memory-shared_ptr.html">shared ptr</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">element_type<span class="sy3">&</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span> <a href="cpp-types-ptrdiff_t.html"><span class="kw101">std::<span class="me2">ptrdiff_t</span></span></a> idx <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<td></td>
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<td></td>
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<td></td>
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</tbody>
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<p>到存储的指针所指向的数组内的下标。</p>
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<p>若存储的指针为空或 <code>idx</code> 为负则行为未定义。</p>
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<p>若 <code>T</code> （ <code>shared_ptr</code> 的模板形参）是数组类型 <code>U[N]</code> ，则 <code>idx</code> 必须小于 <code>N</code> ，否则行为未定义。</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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<tr class="t-par">
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<td>idx</td>
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<td>-</td>
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<td>数组下标</td>
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</tr>
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</table>
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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>到数组第 <code>idx</code> 元素的引用，即 <span class="t-c"><span class="mw-geshi cpp source-cpp">get<span class="br0">(</span><span class="br0">)</span><span class="br0">[</span>idx<span class="br0">]</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>不抛出。</p>
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<h3><span class="mw-headline" id=".E6.8F.90.E9.86.92">提醒</span></h3>
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<p><code>T</code> 不是数组类型时，是否声明此函数是未指定的。若声明此函数，则其返回类型是未指定的，但函数声明保证合法，函数定义未必合法。</p>
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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 <cstddef></span>
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<span class="co2">#include <memory></span>
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<span class="co2">#include <iostream></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">const</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> arr_size <span class="sy1">=</span> <span class="nu0">10</span><span class="sy4">;</span>
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<a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="br0">[</span><span class="br0">]</span><span class="sy1">></span> pis<span class="br0">(</span>new <span class="kw4">int</span><span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span><span class="br0">{</span><span class="nu0">0</span>,<span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span>,<span class="nu0">6</span>,<span class="nu0">7</span>,<span class="nu0">8</span>,<span class="nu0">9</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> arr_size<span class="sy4">;</span> i<span class="sy2">++</span><span class="br0">)</span><span class="br0">{</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> pis<span class="br0">[</span>i<span class="br0">]</span> <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<span class="br0">}</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">0 1 2 3 4 5 6 7 8 9</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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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-shared_ptr-get.html"><span class="t-lines"><span>get</span></span></a></div>
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</div>
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</td>
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<td>返回存储的指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</div>
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<div class="visualClear"></div>
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</body>
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