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<!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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::uninitialized_copy_n</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_uninitialized_copy_n 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>uninitialized_copy_n</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></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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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-memory.html"><memory></a></code></div>
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</td>
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<td></td>
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<td></td>
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</tr>
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<tr class="t-dcl t-since-cxx11">
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<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> InputIt, <span class="kw1">class</span> Size, <span class="kw1">class</span> NoThrowForwardIt <span class="sy1">></span><br />
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NoThrowForwardIt uninitialized_copy_n<span class="br0">(</span> InputIt first, Size count, NoThrowForwardIt d_first <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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<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> ExecutionPolicy, <span class="kw1">class</span> ForwardIt, <span class="kw1">class</span> Size, <span class="kw1">class</span> NoThrowForwardIt <span class="sy1">></span><br /></span>
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<p>NoThrowForwardIt uninitialized_copy_n<span class="br0">(</span> ExecutionPolicy<span class="sy3">&&</span> policy, ForwardIt first, Size count,<br /></p>
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NoThrowForwardIt d_first <span class="br0">)</span><span class="sy4">;</span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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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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<div class="t-li1"><span class="t-li">1)</span> 从始于 <code>first</code> 的范围复制 <code>count</code> 个元素到始于 <code>d_first</code> 的未初始化内存区域，如同以
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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">for</span> <span class="br0">(</span> <span class="sy4">;</span> n <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> <span class="sy2">++</span>d_first, <span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="sy2">++</span>first, <span class="sy2">--</span>n<span class="br0">)</span>
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<span class="sy4">::</span><span class="me2">new</span> <span class="br0">(</span><span class="coMULTI">/*VOIDIFY*/</span><span class="br0">(</span><span class="sy2">*</span>d_first<span class="br0">)</span><span class="br0">)</span>
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<span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>ForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span><span class="br0">(</span><span class="sy2">*</span>first<span class="br0">)</span><span class="sy4">;</span></pre></div>
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</div>
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<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*VOIDIFY*/</span><span class="br0">(</span>e<span class="br0">)</span></span></span> 为：</p>
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<table class="t-rev-begin">
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<tr class="t-rev t-until-cxx20">
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<td>
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<dl>
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<dd><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><a href="cpp-memory-addressof.html"><span class="kw756">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>e<span class="br0">)</span><span class="br0">)</span></span></span></dd>
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</dl>
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</td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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</tr>
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<tr class="t-rev t-since-cxx20">
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<td>
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<dl>
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<dd><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">const_cast</span><span class="sy1"><</span><span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">volatile</span> <span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><a href="cpp-memory-addressof.html"><span class="kw756">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>e<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span></dd>
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</dl>
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</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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</tr>
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</table>
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</div>
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<div class="t-li1"><span class="t-li"></span> 若初始化期间抛异常，则以未指定顺序销毁已构造的对象。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但按照 <code>policy</code> 执行。此重载仅若 <span class="t-rev-inl t-until-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1563">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span><span class="t-rev-inl t-since-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-algorithm-is_execution_policy.html"><span class="kw1563">std::<span class="me2">is_execution_policy_v</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1"><</span>ExecutionPolicy<span class="sy1">>></span></span></span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span> 为 true 才参与重载决议。</div>
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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>first</td>
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<td>-</td>
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<td>要复制的元素范围起始</td>
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</tr>
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<tr class="t-par">
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<td>d_first</td>
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<td>-</td>
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<td>目标范围起始</td>
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</tr>
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<tr class="t-par">
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<td>policy</td>
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<td>-</td>
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<td>所用的执行策略。细节见<a href="cpp-algorithm-execution_policy_tag_t.html">执行策略</a>。</td>
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</tr>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>InputIt</code> 必须满足<a href="cpp-named_req-InputIterator.html"><span style="font-style:italic">老式输入迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyInputIterator)</span></a> 的要求。</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>ForwardIt</code> 必须满足<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>NoThrowForwardIt</code> 必须满足<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a> 的要求。</td>
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</tr>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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通过 <code>NoThrowForwardIt</code> 合法实例的自增、赋值、比较或间接均不可抛异常。</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>指向最后复制的元素后一元素的迭代器。</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>与 <code>count</code> 成线性。</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>拥有名为 <code>ExecutionPolicy</code> 的模板形参的重载按下列方式报告错误：</p>
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<ul>
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<li>若作为算法一部分调用的函数的执行抛出异常，且 <code>ExecutionPolicy</code> 为<a href="cpp-algorithm-execution_policy_tag_t.html">标准策略</a>之一，则调用 <span class="t-lc"><a href="cpp-error-terminate.html">std::terminate</a></span> 。对于任何其他 <code>ExecutionPolicy</code> ，行为是实现定义的。</li>
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<li>若算法无法分配内存，则抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。</li>
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</ul>
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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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<table class="eq-fun-cpp-table">
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<tr>
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<td>
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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">class</span> InputIt, <span class="kw1">class</span> Size, <span class="kw1">class</span> NoThrowForwardIt<span class="sy1">></span>
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NoThrowForwardIt uninitialized_copy_n<span class="br0">(</span>InputIt first, Size count, NoThrowForwardIt d_first<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">using</span> T <span class="sy1">=</span> <span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>NoThrowForwardIt<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span><span class="sy4">;</span>
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NoThrowForwardIt current <span class="sy1">=</span> d_first<span class="sy4">;</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> count <span class="sy1">></span> <span class="nu0">0</span><span class="sy4">;</span> <span class="sy2">++</span>first, <span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="sy2">++</span>current, <span class="sy2">--</span>count<span class="br0">)</span> <span class="br0">{</span>
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<span class="sy4">::</span><span class="me2">new</span> <span class="br0">(</span><span class="kw1">const_cast</span><span class="sy1"><</span><span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">volatile</span> <span class="kw4">void</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>
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<a href="cpp-memory-addressof.html"><span class="kw756">std::<span class="me2">addressof</span></span></a><span class="br0">(</span><span class="sy2">*</span>current<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span> T<span class="br0">(</span><span class="sy2">*</span>first<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="kw1">catch</span> <span class="br0">(</span>...<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> d_first <span class="sy3">!</span><span class="sy1">=</span> current<span class="sy4">;</span> <span class="sy2">++</span>d_first<span class="br0">)</span> <span class="br0">{</span>
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d_first<span class="sy2">-</span><span class="sy1">></span>~T<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">throw</span><span class="sy4">;</span>
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||||
<span class="br0">}</span>
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<span class="kw1">return</span> current<span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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</td>
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</tr>
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</table>
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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">
|
||||
<div class="t-example-live-link"></div>
|
||||
<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 <algorithm></span>
|
||||
<span class="co2">#include <iostream></span>
|
||||
<span class="co2">#include <memory></span>
|
||||
<span class="co2">#include <string></span>
|
||||
<span class="co2">#include <tuple></span>
|
||||
<span class="co2">#include <vector></span>
|
||||
|
||||
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
||||
<span class="br0">{</span>
|
||||
<a href="cpp-container-vector.html"><span class="kw1268">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">></span> v <span class="sy1">=</span> <span class="br0">{</span><span class="st0">"This"</span>, <span class="st0">"is"</span>, <span class="st0">"an"</span>, <span class="st0">"example"</span><span class="br0">}</span><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><span class="sy2">*</span> p<span class="sy4">;</span>
|
||||
<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> sz<span class="sy4">;</span>
|
||||
<a href="cpp-utility-tuple-tie.html"><span class="kw1112">std::<span class="me2">tie</span></span></a><span class="br0">(</span>p, sz<span class="br0">)</span> <span class="sy1">=</span> <a href="cpp-memory-get_temporary_buffer.html"><span class="kw730">std::<span class="me2">get_temporary_buffer</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">></span><span class="br0">(</span>v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
sz <span class="sy1">=</span> <a href="cpp-algorithm-min.html"><span class="kw1641">std::<span class="me2">min</span></span></a><span class="br0">(</span>sz, v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
|
||||
std<span class="sy4">::</span><span class="me2">uninitialized_copy_n</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, sz, p<span class="br0">)</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy2">*</span> i <span class="sy1">=</span> p<span class="sy4">;</span> i <span class="sy3">!</span><span class="sy1">=</span> p<span class="sy2">+</span>sz<span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
|
||||
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="sy2">*</span>i <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
|
||||
i<span class="sy2">-</span><span class="sy1">></span>~basic_string<span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
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||||
<a href="cpp-memory-return_temporary_buffer.html"><span class="kw731">std::<span class="me2">return_temporary_buffer</span></span></a><span class="br0">(</span>p<span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span></pre></div>
|
||||
</div>
|
||||
<p>输出：</p>
|
||||
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
||||
<div class="text source-text">
|
||||
<pre class="de1">This is an example</pre></div>
|
||||
</div>
|
||||
</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">
|
||||
<tr class="t-dsc">
|
||||
<td>
|
||||
<div class="t-dsc-member-div">
|
||||
<div><a href="cpp-memory-uninitialized_copy.html"><span class="t-lines"><span>uninitialized_copy</span></span></a></div>
|
||||
</div>
|
||||
</td>
|
||||
<td>将范围内的对象复制到未初始化的内存区域<br />
|
||||
<span class="t-mark">(函数模板)</span></td>
|
||||
</tr>
|
||||
<tr class="t-dsc">
|
||||
<td>
|
||||
<div class="t-dsc-member-div">
|
||||
<div><a href="cpp-memory-ranges-uninitialized_copy_n.html"><span class="t-lines"><span>ranges::uninitialized_copy_n</span></span></a></div>
|
||||
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
||||
</div>
|
||||
</td>
|
||||
<td>复制一定量元素到未初始化的内存区域<br />
|
||||
<span class="t-mark">(niebloid)</span></td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
<div class="visualClear"></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user