120 lines
8.0 KiB
HTML
120 lines
8.0 KiB
HTML
<!DOCTYPE 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::deque<T,Allocator>::at</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_deque_at skin-cppreference2 action-view cpp-page-template 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::deque<T,Allocator>::</span>at</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-deque.html">deque</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div class="t-page-template" style="">
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<p></p>
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</div>
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl t-since-cxx98">
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<td class="t-dcl-nopad">
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<div><span class="mw-geshi cpp source-cpp">reference at<span class="br0">(</span> size_type pos <span class="br0">)</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 class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-cxx98">
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<div><span class="mw-geshi cpp source-cpp">const_reference at<span class="br0">(</span> size_type pos <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 class="t-dcl-nopad"></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>返回位于指定位置 <code>pos</code> 的元素的引用，有边界检查。</p>
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<p>若 <code>pos</code> 不在容器范围内，则抛出 <span class="t-lc"><a href="cpp-error-out_of_range.html">std::out_of_range</a></span> 类型的异常。</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>pos</td>
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<td>-</td>
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<td>要返回的元素的位置</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>到所需元素的引用。</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>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>pos <span class="sy1"><</span> size<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 则抛出 <span class="t-lc"><a href="cpp-error-out_of_range.html">std::out_of_range</a></span></p>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<p>常数。</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 <iostream></span>
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<span class="co2">#include <deque></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-deque.html"><span class="kw1271">std::<span class="me2">deque</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> data <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">4</span>, <span class="nu0">5</span>, <span class="nu0">5</span>, <span class="nu0">6</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="co1">// Set element 1</span>
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data.<span class="me1">at</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy1">=</span> <span class="nu0">88</span><span class="sy4">;</span>
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<span class="co1">// Read element 2</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> <span class="st0">"Element at index 2 has value "</span> <span class="sy1"><<</span> data.<span class="me1">at</span><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</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> <span class="st0">"data size = "</span> <span class="sy1"><<</span> data.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<span class="co1">// Set element 6</span>
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data.<span class="me1">at</span><span class="br0">(</span><span class="nu0">6</span><span class="br0">)</span> <span class="sy1">=</span> <span class="nu0">666</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">catch</span> <span class="br0">(</span><a href="cpp-error-out_of_range.html"><span class="kw768">std::<span class="me2">out_of_range</span></span></a> <span class="kw4">const</span><span class="sy3">&</span> exc<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> exc.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</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="co1">// Print final values</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> <span class="st0">"data:"</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> elem <span class="sy4">:</span> data<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> <span class="st0">" "</span> <span class="sy1"><<</span> elem<span class="sy4">;</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> <span class="st0">'<span class="es1">\n</span>'</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>可能的输出：</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">Element at index 2 has value 4
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data size = 6
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deque::_M_range_check: __n (which is 6)>= this->size() (which is 6)
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data: 1 88 4 5 5 6</pre></div>
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</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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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-deque-operator_at.html"><span class="t-lines"><span>operator[]</span></span></a></div>
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</div>
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</td>
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<td>访问指定的元素<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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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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