116 lines
8.6 KiB
HTML
116 lines
8.6 KiB
HTML
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<title>std::basic_string<CharT,Traits,Allocator>::operator basic_string_view</title>
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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>operator basic_string_view</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">operator <a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><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 class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 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> operator <a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><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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<p>返回如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="br0">(</span>data<span class="br0">(</span><span class="br0">)</span>, size<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 构造的 <span class="t-lc"><a href="cpp-string-basic_string_view.html">std::basic_string_view</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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<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>表示整个字符串内容的字符串视图。</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>程序员负责确保返回的字符串视图不会生存超过字符串的生存期。</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"><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> get_string<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> f<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> sv<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> x <span class="sy1">=</span> f<span class="br0">(</span>get_string<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
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<a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> sv <span class="sy1">=</span> get_string<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 坏：保有悬垂指针</span></pre></div>
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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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <string_view></span>
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<span class="kw4">void</span> show_wstring_size<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1250">std::<span class="me2">wstring_view</span></span></a> wcstr_v<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> wcstr_v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" code points<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</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> cppstr <span class="sy1">=</span> <span class="st0">"ラーメン"</span><span class="sy4">;</span> <span class="co1">// 窄字符串</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> wcstr <span class="sy1">=</span> L<span class="st0">"ラーメン"</span><span class="sy4">;</span> <span class="co1">// 宽字符串</span>
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<span class="co1">// 从 string 隐式转换到 string_view</span>
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<span class="co1">// 经由 std::string::operator string_view ：</span>
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<a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> cppstr_v <span class="sy1">=</span> cppstr<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> cppstr_v <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> cppstr_v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" code units<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="co1">// 从 wstring 隐式转换到 wstring_view</span>
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<span class="co1">// 经由 std::wstring::operator wstring_view ：</span>
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show_wstring_size<span class="br0">(</span>wcstr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<p>输出：</p>
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<div class="text source-text">
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<pre class="de1">ラーメン
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12 code units
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4 code points</pre></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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<div><a href="cpp-string-basic_string_view-basic_string_view.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造 <code>basic_string_view</code><br />
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<span class="t-mark">(<code>std::basic_string_view<CharT,Traits></code> 的公开成员函数)</span></td>
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