219 lines
20 KiB
HTML
219 lines
20 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::ranges::uninitialized_copy_n, std::ranges::uninitialized_copy_n_result</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_ranges_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::ranges::</span>uninitialized_copy_n, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>uninitialized_copy_n_result</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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<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></td>
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<td></td>
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<td></td>
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<tr class="t-dcl-h">
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<div>调用签名</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-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I, no<span class="sy2">-</span>throw<span class="sy2">-</span>input<span class="sy2">-</span>iterator O, no<span class="sy2">-</span>throw<span class="sy2">-</span>sentinel<span class="sy2">-</span><span class="kw1">for</span><span class="sy1"><</span>O<span class="sy1">></span> S <span class="sy1">></span><br /></span>
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<p>requires std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>O<span class="sy1">></span>, std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>I<span class="sy1">>></span><br />
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uninitialized_copy_n_result<span class="sy1"><</span>I, O<span class="sy1">></span><br />
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uninitialized_copy_n<span class="br0">(</span> I ifirst, std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">></span> count,<br /></p>
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O ofirst, S olast <span class="br0">)</span><span class="sy4">;</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-cxx20">(C++20 起)</span></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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<div>辅助类型</div>
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<td></td>
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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> I, <span class="kw1">class</span> O<span class="sy1">></span><br />
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<span class="kw1">using</span> uninitialized_copy_n_result <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">in_out_result</span><span class="sy1"><</span>I, O<span class="sy1">></span><span class="sy4">;</span></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-cxx20">(C++20 起)</span></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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<p>令 <span class="mjax" style="display:none">\(\scriptsize N\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">N</span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">min</span><span class="br0">(</span>count, ranges<span class="sy4">::</span><span class="me2">distance</span><span class="br0">(</span>ofirst, olast<span class="br0">)</span><span class="br0">)</span></span></span> ，以始于 <code>ifirst</code> 的输入范围的元素为来源，在作为未初始化内存区域的输出范围 <code>[ofirst, olast)</code> 中构造 <span class="mjax" style="display:none">\(\scriptsize N\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">N</span> 个元素。</p>
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<p>输入范围 <code>[ifirst, ifirst + count)</code> 必须不与输出范围 <code>[ofirst, olast)</code> 重叠。</p>
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<p>若在初始化期间抛异常，则以未指定顺序销毁已构造的元素。</p>
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<p>函数所拥有的效果等价于：</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">auto</span> ret <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">uninitialized_copy</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="br0">(</span>ifirst, count<span class="br0">)</span>,
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std<span class="sy4">::</span><span class="me2">default_sentinel</span>, ofirst, olast<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="br0">{</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>ret.<span class="me1">in</span><span class="br0">)</span>.<span class="me1">base</span><span class="br0">(</span><span class="br0">)</span>, ret.<span class="me1">out</span><span class="br0">}</span><span class="sy4">;</span></pre></div>
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</div>
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<p>此页面上描述的仿函数实体是 <i>niebloid</i> ，即：</p>
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<ul>
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<li>调用它们中的任何一者时不可指定显式模板实参。</li>
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<li>它们无一对<a href="cpp-language-adl.html">实参依赖查找</a>可见。</li>
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<li>在<a href="cpp-language-unqualified_lookup.html">通常无限定查找</a>寻找函数调用运算符左侧的名称找到它们之一时，它禁止<a href="cpp-language-adl.html">实参依赖查找</a>。</li>
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</ul>
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<p>实际上，它们能以函数对象，或以某些特殊编译器扩展实现。</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>ifirst</td>
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<td>-</td>
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<td>要复制的元素范围的起始</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td>要复制的元素数</td>
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</tr>
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<tr class="t-par">
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<td>ofirst, olast</td>
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<td>-</td>
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<td>目标范围</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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span>ifirst <span class="sy2">+</span> N, ofirst <span class="sy2">+</span> N<span class="br0">}</span></span></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><span class="mjax" style="display:none">\(\scriptsize\mathcal{O}(N)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">𝓞(N)</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>构造目标范围中的元素时抛出的异常，若存在。</p>
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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>若输出范围的值类型为<a href="cpp-named_req-TrivialType.html"><span style="font-style:italic">平凡类型</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(TrivialType)</span></a> ，则实现可能提升 <code>ranges::uninitialized_copy_n</code> 的效率，例如用 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">copy_n</span></span></span> 。</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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<table class="eq-fun-cpp-table">
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<tr>
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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">struct</span> uninitialized_copy_n_fn <span class="br0">{</span>
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<span class="kw1">template</span> <span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">input_iterator</span> I, no<span class="sy2">-</span>throw<span class="sy2">-</span>input<span class="sy2">-</span>iterator O, no<span class="sy2">-</span>throw<span class="sy2">-</span>sentinel<span class="sy2">-</span><span class="kw1">for</span><span class="sy1"><</span>O<span class="sy1">></span> S<span class="sy1">></span>
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requires std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>O<span class="sy1">></span>, std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>I<span class="sy1">>></span>
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ranges<span class="sy4">::</span><span class="me2">uninitialized_copy_n_result</span><span class="sy1"><</span>I, O<span class="sy1">></span>
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operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I ifirst, std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">></span> count, O ofirst, S olast <span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
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O current <span class="br0">{</span>ofirst<span class="br0">}</span><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="sy3">&&</span> current <span class="sy3">!</span><span class="sy1">=</span> olast<span class="sy4">;</span> <span class="sy2">++</span>ifirst, <span class="sy2">++</span>current, <span class="sy2">--</span>count<span class="br0">)</span>
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ranges<span class="sy4">::</span><span class="me2">construct_at</span><span class="br0">(</span><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span><span class="sy2">*</span>current<span class="br0">)</span>, <span class="sy2">*</span>ifirst<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="br0">{</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>ifirst<span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>current<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</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> <span class="co1">// 回滚：销毁构造的元素</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;</span> ofirst <span class="sy3">!</span><span class="sy1">=</span> current<span class="sy4">;</span> <span class="sy2">++</span>ofirst<span class="br0">)</span>
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ranges<span class="sy4">::</span><span class="me2">destroy_at</span><span class="br0">(</span><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span><span class="sy2">*</span>ofirst<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</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="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">inline</span> <span class="kw4">constexpr</span> uninitialized_copy_n_fn uninitialized_copy_n<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</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">
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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 <iomanip></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <memory></span>
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<span class="co2">#include <string></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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<span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> stars<span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span> <span class="st0">"Procyon"</span>, <span class="st0">"Spica"</span>, <span class="st0">"Pollux"</span>, <span class="st0">"Deneb"</span>, <span class="st0">"Polaris"</span>, <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> n <span class="br0">{</span><span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
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alignas<span class="br0">(</span>alignof<span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">)</span><span class="br0">)</span> <span class="kw4">char</span> out<span class="br0">[</span>n <span class="sy2">*</span> sizeof<span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">)</span><span class="br0">]</span><span class="sy4">;</span>
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<span class="kw1">try</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> first <span class="br0">{</span><span class="kw1">reinterpret_cast</span><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span>out<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">auto</span> last <span class="br0">{</span>first <span class="sy2">+</span> n<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">auto</span> ret <span class="br0">{</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">uninitialized_copy_n</span><span class="br0">(</span><a href="cpp-iterator-begin.html"><span class="kw676">std::<span class="me2">begin</span></span></a><span class="br0">(</span>stars<span class="br0">)</span>, n, first, last<span class="br0">)</span><span class="br0">}</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">"{ "</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> it <span class="br0">{</span>first<span class="br0">}</span><span class="sy4">;</span> it <span class="sy3">!</span><span class="sy1">=</span> ret.<span class="me1">out</span><span class="sy4">;</span> <span class="sy2">++</span>it<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> <a href="cpp-io-manip-quoted.html"><span class="kw1802">std::<span class="me2">quoted</span></span></a><span class="br0">(</span><span class="sy2">*</span>it<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">", "</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">"};<span class="es1">\n</span>"</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">destroy</span><span class="br0">(</span>first, last<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">catch</span><span class="br0">(</span>...<span class="br0">)</span>
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<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">"uninitialized_copy_n exception<span class="es1">\n</span>"</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">{ "Procyon", "Spica", "Pollux", "Deneb", };</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-memory-ranges-uninitialized_copy.html"><span class="t-lines"><span>ranges::uninitialized_copy</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>复制元素范围到未初始化的内存区域<br />
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<span class="t-mark">(niebloid)</span></td>
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</tr>
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-uninitialized_copy_n.html"><span class="t-lines"><span>uninitialized_copy_n</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>将指定数量的对象复制到未初始化的内存区域<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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