124 lines
11 KiB
HTML
124 lines
11 KiB
HTML
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<title>std::basic_string<CharT,Traits,Allocator>::resize_and_overwrite</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_basic_string_resize_and_overwrite 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>resize_and_overwrite</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 id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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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> Operation <span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <span class="kw4">void</span> resize_and_overwrite<span class="br0">(</span> size_type count, Operation op <span class="br0">)</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-since-cxx23">(C++23 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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<p>重设字符串大小以含有至多 <code>count</code> 个字符，用用户提供的操作 <code>op</code> 修改可能不确定的内容并设置长度。</p>
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<p>此函数执行下列步骤：</p>
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<ol>
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<li>获得至少含有 <span class="t-c"><span class="mw-geshi cpp source-cpp">count <span class="sy2">+</span> <span class="nu0">1</span></span></span> 个字符的存储，并使其前 <code>k</code> 个字符等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的前 <code>k</code> 个字符，其中 <code>k</code> 是 <code>count</code> 与调用 <code>resize_and_overwrite</code> 前 <span class="t-c"><span class="mw-geshi cpp source-cpp">this<span class="sy2">-</span><span class="sy1">></span>size<span class="br0">(</span><span class="br0">)</span></span></span> 的结果的较小者。令 <code>p</code> 代表指向该存储中首个字符的指针。
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<ul>
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<li>相等性以如同通过检查 <span class="t-c"><span class="mw-geshi cpp source-cpp">this<span class="sy2">-</span><span class="sy1">></span>compare<span class="br0">(</span><span class="nu0">0</span>, k, p, k<span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span> 确定。</li>
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<li><code>[p + k, p + count]</code> 中的字符可能拥有不确定值。</li>
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</ul>
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</li>
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<li>求值 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>op<span class="br0">)</span><span class="br0">(</span>p, count<span class="br0">)</span></span></span> 。令 <code>r</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>op<span class="br0">)</span><span class="br0">(</span>p, count<span class="br0">)</span></span></span> 的返回值。</li>
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<li>以 <code>[p, p + r)</code> 替换 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的内容（这会设置 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的长度为 <code>r</code> ）。非法化所有指向范围 <code>[p, p + count]</code> 中的指针与引用。</li>
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</ol>
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<p>若 <code>r</code> 不具有<a href="cpp-iterator-weakly_incrementable.html#.E6.95.B4.E6.95.B0.E5.BC.8F.E7.B1.BB.E5.9E.8B">整数式类型</a>则程序非良构。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>op<span class="br0">)</span><span class="br0">(</span>p, count<span class="br0">)</span></span></span> 抛出异常或修改 <code>p</code> 或 <code>count</code>、 <code>r</code> 不在范围 <code>[0, count]</code> 中，或范围 <code>[p, p + r)</code> 中的任何字符拥有不确定值，则行为未定义。</p>
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<p>推荐实现避免不必要的复制与分配，例如通过使得 <code>p</code> 等于指向调用后为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 分配的字符存储的起始指针，若 <code>count</code> 小于或等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">this<span class="sy2">-</span><span class="sy1">></span>capacity<span class="br0">(</span><span class="br0">)</span></span></span> 则该存储能等同于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 的既存存储。</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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<td>count</td>
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<td>-</td>
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<td>字符串的最大可能的新大小</td>
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</tr>
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<td>op</td>
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<td>-</td>
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<td>用于设置字符串新内容的函数对象</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>（无）</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">count <span class="sy1">></span> max_size<span class="br0">(</span><span class="br0">)</span></span></span> 则为 <span class="t-lc"><a href="cpp-error-length_error.html">std::length_error</a></span> 。任何对应的 <code>Allocator</code> 所抛的异常。</p>
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<p>若从 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>op<span class="br0">)</span><span class="br0">(</span>p, count<span class="br0">)</span></span></span> 抛出异常，则行为未定义。否则若抛出异常则此函数无效果。</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>无论重分配是否出现， <code>resize_and_overwrite</code> 都非法化所有指向 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 中的迭代器、指针及引用。实现可以假设调用 <code>resize_and_overwrite</code> 后字符串的内容不会被别名化。</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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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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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-resize.html"><span class="t-lines"><span>resize</span></span></a></div>
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</div>
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</td>
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<td>更改存储的字符数<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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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-unique_ptr-make_unique.html"><span class="t-lines"><span>make_unique</span><span>make_unique_for_overwrite</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span><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>创建管理一个新对象的独占指针<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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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-shared_ptr-make_shared.html"><span class="t-lines"><span>make_shared</span><span>make_shared_for_overwrite</span></span></a></div>
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<div><span class="t-lines"><span></span><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>创建管理一个新对象的共享指针<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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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-shared_ptr-allocate_shared.html"><span class="t-lines"><span>allocate_shared</span><span>allocate_shared_for_overwrite</span></span></a></div>
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<div><span class="t-lines"><span></span><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>创建管理一个用分配器分配的新对象的共享指针<br />
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<span class="t-mark">(函数模板)</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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