109 lines
6.1 KiB
HTML
109 lines
6.1 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::basic_string<CharT,Traits,Allocator>::copy</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_basic_string_copy 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::basic_string<CharT,Traits,Allocator>::</span>copy</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-string.html">string</a>‎ | <a href="cpp-string-basic_string.html">basic string</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">size_type copy<span class="br0">(</span> CharT<span class="sy2">*</span> dest, size_type count, size_type pos <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> size_type copy<span class="br0">(</span> CharT<span class="sy2">*</span> dest, size_type count, size_type pos <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>复制子串 <code>[pos, pos+count)</code> 到 <code>dest</code> 所指向的字符串。若请求的子串越过 string 结尾，或若 <span class="t-c"><span class="mw-geshi cpp source-cpp">count <span class="sy1">==</span> npos</span></span> ，则复制的子串为 <code>[pos, size())</code> 。产生的字符串不是空终止的。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">pos <span class="sy1">></span> size<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=".E5.8F.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>dest</td>
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<td>-</td>
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<td>指向目标字符串的指针</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>子串长度</td>
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</tr>
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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>包含的首字符位置</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>复制的字符数</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">pos <span class="sy1">></span> size<span class="br0">(</span><span class="br0">)</span></span></span> 则为 <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>与 <code>count</code> 成线性</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 <string></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>
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<span class="br0">{</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> foo<span class="br0">(</span><span class="st0">"quuuux"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> bar<span class="br0">[</span><span class="nu0">7</span><span class="br0">]</span><span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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foo.<span class="me1">copy</span><span class="br0">(</span>bar, sizeof bar<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> bar <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>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">quuuux</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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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-substr.html"><span class="t-lines"><span>substr</span></span></a></div>
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</div>
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</td>
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<td>返回子串<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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</body>
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