166 lines
9.8 KiB
HTML
166 lines
9.8 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::codecvt_mode</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_locale_codecvt_mode skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>codecvt_mode</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-locale.html">locale</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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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><a href="cpp-header-codecvt.html"><codecvt></a></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx11">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw2">enum</span> codecvt_mode <span class="br0">{</span><br /></span>
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<p> consume_header <span class="sy1">=</span> <span class="nu0">4</span>,<br />
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generate_header <span class="sy1">=</span> <span class="nu0">2</span>,<br />
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little_endian <span class="sy1">=</span> <span class="nu0">1</span><br /></p>
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<span class="br0">}</span><span class="sy4">;</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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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">(C++17 中弃用)</span></td>
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</tr>
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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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</tbody>
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</table>
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<p>平面 <span class="t-lc"><a href="cpp-locale-codecvt_utf8.html">std::codecvt_utf8</a></span> 、 <span class="t-lc"><a href="cpp-locale-codecvt_utf16.html">std::codecvt_utf16</a></span> 和 <span class="t-lc"><a href="cpp-locale-codecvt_utf8_utf16.html">std::codecvt_utf8_utf16</a></span> 接受可选的 <span class="t-lc"><strong class="selflink">std::codecvt_mode</strong></span> 类型值为模板实参，这会指定 unicode 字符串转换的可选特性。</p>
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<h3><span class="mw-headline" id=".E5.B8.B8.E9.87.8F">常量</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-header">
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<td colspan="2">
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<div>定义于头文件 <code><a href="cpp-header-locale.html"><locale></a></code></div>
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</td>
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</tr>
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<tr class="t-dsc-hitem">
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<td>值</td>
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<td>含义</td>
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</tr>
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<tr class="t-dsc">
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<td><code>little_endian</code></td>
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<td>假设输入是小端序（仅应用于 UTF-16 ，默认为大端序）</td>
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</tr>
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<tr class="t-dsc">
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<td><code>consume_header</code></td>
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<td>若输入序列的开始存在字节序标记，则消耗它，而且（在 UTF-16 的情况下）依赖于为解码剩下输入而指定的字节序</td>
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</tr>
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<tr class="t-dsc">
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<td><code>generate_header</code></td>
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<td>在输出序列的开始输出字节序标记</td>
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</tr>
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</table>
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<p>受到辨认的字节序标记为：</p>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td><code>0xfe 0xff</code></td>
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<td>UTF-16 大端</td>
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</tr>
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<tr class="t-dsc">
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<td><code>0xff 0xfe</code></td>
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<td>UTF-16 小端</td>
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</tr>
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<tr class="t-dsc">
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<td><code>0xef 0xbb 0xbf</code></td>
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<td>UTF-8 （端序无影响）</td>
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</tr>
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</table>
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<p>若在读以字节序标记开始的文件时未指定 <span class="t-lc"><strong class="selflink">std::consume_header</strong></span> ，则将 Unicode 字符 U+FEFF （零宽无中断空格）读作字符串内容的首字符。</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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<p>下列示例演示消耗 UTF-8 BOM</p>
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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 <fstream></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <locale></span>
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<span class="co2">#include <codecvt></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="co1">// 带 BOM 的 UTF-8 数据</span>
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<a href="cpp-io-basic_ofstream.html"><span class="kw1733">std::<span class="me2">ofstream</span></span></a><span class="br0">(</span><span class="st0">"text.txt"</span><span class="br0">)</span> <span class="sy1"><<</span> u8<span class="st0">"<span class="es3">\ufeff</span>z<span class="es3">\u6c34</span><span class="es4">\U0001d10b</span>"</span><span class="sy4">;</span>
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<span class="co1">// 读 UTF8 文件，跳过 BOM</span>
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<a href="cpp-io-basic_ifstream.html"><span class="kw1746">std::<span class="me2">wifstream</span></span></a> fin<span class="br0">(</span><span class="st0">"text.txt"</span><span class="br0">)</span><span class="sy4">;</span>
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fin.<span class="me1">imbue</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span>fin.<span class="me1">getloc</span><span class="br0">(</span><span class="br0">)</span>,
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new <a href="cpp-locale-codecvt_utf8.html"><span class="kw1983">std::<span class="me2">codecvt_utf8</span></span></a><span class="sy1"><</span><span class="kw4">wchar_t</span>, <span class="nu12">0x10ffff</span>, std<span class="sy4">::</span><span class="me2">consume_header</span><span class="sy1">></span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">wchar_t</span> c<span class="sy4">;</span> fin.<span class="me1">get</span><span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</span> <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-hex.html"><span class="kw1782">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-showbase.html"><span class="kw1766">std::<span class="me2">showbase</span></span></a> <span class="sy1"><<</span> c <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">0x7a
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0x6c34
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0x1d10b</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-locale-codecvt.html"><span class="t-lines"><span>codecvt</span></span></a></div>
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</div>
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</td>
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<td>在字符编码间转换，包括 UTF-8、UTF-16、UTF-32<br />
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<span class="t-mark">(类模板)</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-locale-codecvt_utf8.html"><span class="t-lines"><span>codecvt_utf8</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 class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span></span></span></div>
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</div>
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</td>
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<td>在 UTF-8 与 UCS2/UCS4 间转换<br />
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<span class="t-mark">(类模板)</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-locale-codecvt_utf16.html"><span class="t-lines"><span>codecvt_utf16</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 class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span></span></span></div>
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</div>
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</td>
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<td>在 UTF-16 与 UCS2/UCS4 间转换<br />
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<span class="t-mark">(类模板)</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-locale-codecvt_utf8_utf16.html"><span class="t-lines"><span>codecvt_utf8_utf16</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 class="t-mark-rev t-deprecated-cxx17">(C++17 中弃用)</span></span></span></div>
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</div>
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</td>
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<td>在 UTF-8 与 UTF-16 间转换<br />
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<span class="t-mark">(类模板)</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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</div>
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</div>
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</body>
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</html>
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