147 lines
11 KiB
HTML
147 lines
11 KiB
HTML
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<title>std::basic_string<CharT,Traits,Allocator>::c_str</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_basic_string_c_str 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>c_str</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-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="kw4">const</span> CharT<span class="sy2">*</span> c_str<span class="br0">(</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-cxx11">(C++11 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> CharT<span class="sy2">*</span> c_str<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<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> <span class="kw4">const</span> CharT<span class="sy2">*</span> c_str<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</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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</tbody>
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<tbody>
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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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</table>
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<p>返回指向拥有数据等价于存储于字符串中的空终止字符数组的指针。</p>
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<p>该指针有范围 <code>[c_str(); c_str() + size()]</code> 为合法，且其中的值对应存储于字符串的值，且在最后位置有个附加的空终止字符。</p>
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<p>从 <code>c_str()</code> 获得的指针可能被下列行为非法化：</p>
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<ul>
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<li>传递给任何非标准库函数字符串的非 const 引用，或</li>
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<li>在字符串上调用非 const 成员函数，包括 <span class="t-lc"><a href="cpp-string-basic_string-operator_at.html">operator[]</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-at.html">at()</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-front.html">front()</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-back.html">back()</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-begin.html">begin()</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-rbegin.html">rbegin()</a></span> 、 <span class="t-lc"><a href="cpp-string-basic_string-end.html">end()</a></span> 及 <span class="t-lc"><a href="cpp-string-basic_string-rend.html">rend()</a></span> 。</li>
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</ul>
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<p>通过 <code>c_str()</code> 写入字符数组是未定义行为。</p>
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<p><code>c_str()</code> 与 <span class="t-lc"><a href="cpp-string-basic_string-data.html">data()</a></span> 进行同一功能。</p>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</p>
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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>指向底层字符存储的指针。</p>
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<p>对于每个 <code>[0, size())</code> 中的 <code>i</code> 有 <span class="t-c"><span class="mw-geshi cpp source-cpp">c_str<span class="br0">(</span><span class="br0">)</span><span class="br0">[</span>i<span class="br0">]</span> <span class="sy1">==</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span>i<span class="br0">)</span></span></span> 。</p>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<p>对于每个 <code>[0, size()]</code> 中的 <code>i</code> 有 <span class="t-c"><span class="mw-geshi cpp source-cpp">c_str<span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> i <span class="sy1">==</span> <a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span>i<span class="br0">)</span><span class="br0">)</span></span></span> 。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>从 <code>c_str()</code> 获得的指针可以只当做一个指向空终止字符串的指针，若 string 对象不含其他空字符。</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 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>
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<span class="co2">#include <cassert></span>
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<span class="co2">#include <cstring></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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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> <span class="kw4">const</span> s<span class="br0">(</span><span class="st0">"Emplary"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span>s.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <a href="cpp-string-byte-strlen.html"><span class="kw1145">std::<span class="me2">strlen</span></span></a><span class="br0">(</span>s.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span><a href="cpp-algorithm-equal.html"><span class="kw1573">std::<span class="me2">equal</span></span></a><span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span><a href="cpp-algorithm-equal.html"><span class="kw1573">std::<span class="me2">equal</span></span></a><span class="br0">(</span>s.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> s.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>, s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span><span class="nu0">0</span> <span class="sy1">==</span> <span class="sy2">*</span><span class="br0">(</span>s.<span class="me1">c_str</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> s.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></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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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-front.html"><span class="t-lines"><span>front</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>访问首字符<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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-back.html"><span class="t-lines"><span>back</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>访问最后的字符<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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-data.html"><span class="t-lines"><span>data</span></span></a></div>
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</div>
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</td>
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<td>返回指向字符串首字符的指针<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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