155 lines
13 KiB
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155 lines
13 KiB
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<title>std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>::to_bytes</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>::</span>to_bytes</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-locale.html">locale</a>‎ | <a href="cpp-locale-wstring_convert.html">wstring convert</a></span></div>
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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></td>
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<div><span class="mw-geshi cpp source-cpp">byte_string to_bytes<span class="br0">(</span> Elem wchar <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp">byte_string to_bytes<span class="br0">(</span> <span class="kw4">const</span> Elem<span class="sy2">*</span> wptr <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">byte_string to_bytes<span class="br0">(</span> <span class="kw4">const</span> wide_string<span class="sy3">&</span> wstr <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">byte_string to_bytes<span class="br0">(</span> <span class="kw4">const</span> Elem<span class="sy2">*</span> first, <span class="kw4">const</span> Elem<span class="sy2">*</span> last<span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>用构造时提供的 <code>codecvt</code> 平面进行宽到多字节转换。</p>
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<div class="t-li1"><span class="t-li">1)</span> 转换 <code>wchar</code> 为 <code>byte_string</code> ，如同它是长为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span> 的字符串。</div>
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<div class="t-li1"><span class="t-li">2)</span> 转换始于 <code>wptr</code> 所指向宽字符的空终止宽字符序列为 <code>byte_string</code> 。</div>
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<div class="t-li1"><span class="t-li">3)</span> 转换宽字符串 <code>str</code> 为 <code>byte_string</code> 。</div>
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<div class="t-li1"><span class="t-li">4)</span> 转换宽字符序列 <code>[first, last)</code> 为 <code>byte_string</code> 。</div>
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<p>所有情况下，转换始于初始迁移状态，除非提供给此 <code>wstring_convert</code> 的构造函数非初始起始状态。记忆转换的字符数和转换状态的终止，并且能以 <span class="t-lc"><a href="cpp-locale-wstring_convert-state.html">state()</a></span> 和 <span class="t-lc"><a href="cpp-locale-wstring_convert-converted.html">converted()</a></span> 访问它们。</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>含有宽到多字节转换结果的 <code>byte_string</code> 对象。若转换失败，且有用户提供的字节错误字符串提供给此 <code>wstring_convert</code> 的构造函数，则返回该字节错误字符串。</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>若此 <code>wstring_convert</code> 不以用户提供的字节错误字符串构造，则在转换失败时抛出 <span class="t-lc"><a href="cpp-error-range_error.html">std::range_error</a></span> 。</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="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 <locale></span>
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<span class="co2">#include <codecvt></span>
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<span class="co2">#include <iomanip></span>
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<span class="co1">// 输出用的工具函数</span>
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<span class="kw4">void</span> hex_print<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy3">&</span> s<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> <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-setfill.html"><span class="kw1795">std::<span class="me2">setfill</span></span></a><span class="br0">(</span><span class="st0">'0'</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">unsigned</span> <span class="kw4">char</span> c <span class="sy4">:</span> s<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-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span>c<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</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> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">dec</span></span></a> <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>
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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">// 宽字符数据</span>
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<a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a> wstr <span class="sy1">=</span> L<span class="st0">"z<span class="es3">\u00df</span><span class="es3">\u6c34</span><span class="es4">\U0001f34c</span>"</span><span class="sy4">;</span> <span class="co1">// 或 L"zß水🍌"</span>
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<span class="co1">// 宽到 UTF-8</span>
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<a href="cpp-locale-wstring_convert.html"><span class="kw1899">std::<span class="me2">wstring_convert</span></span></a><span class="sy1"><</span><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="sy1">>></span> conv1<span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> u8str <span class="sy1">=</span> conv1.<span class="me1">to_bytes</span><span class="br0">(</span>wstr<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> <span class="st0">"UTF-8 conversion produced "</span> <span class="sy1"><<</span> u8str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" bytes:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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hex_print<span class="br0">(</span>u8str<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 宽到 UTF-16le</span>
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<a href="cpp-locale-wstring_convert.html"><span class="kw1899">std::<span class="me2">wstring_convert</span></span></a><span class="sy1"><</span><a href="cpp-locale-codecvt_utf16.html"><span class="kw1984">std::<span class="me2">codecvt_utf16</span></span></a><span class="sy1"><</span><span class="kw4">wchar_t</span>, <span class="nu12">0x10ffff</span>, <a href="cpp-locale-codecvt_mode.html"><span class="kw1989">std::<span class="me2">little_endian</span></span></a><span class="sy1">>></span> conv2<span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> u16str <span class="sy1">=</span> conv2.<span class="me1">to_bytes</span><span class="br0">(</span>wstr<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> <span class="st0">"UTF-16le conversion produced "</span> <span class="sy1"><<</span> u16str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" bytes:<span class="es1">\n</span>"</span><span class="sy4">;</span>
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hex_print<span class="br0">(</span>u16str<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">UTF-8 conversion produced 10 bytes:
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7a c3 9f e6 b0 b4 f0 9f 8d 8c
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UTF-16le conversion produced 10 bytes:
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7a 00 df 00 34 6c 3c d8 4c df</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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<div class="t-dsc-member-div">
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<div><a href="cpp-locale-wstring_convert-from_bytes.html"><span class="t-lines"><span>from_bytes</span></span></a></div>
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</div>
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<td>转换字节字符串为宽字符串<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-wcsrtombs.html"><span class="t-lines"><span>wcsrtombs</span></span></a></div>
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</div>
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</td>
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<td>给定状态，转换宽字符串为窄多字节字符串<br />
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<span class="t-mark">(函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-locale-codecvt-out.html"><span class="t-lines"><span>do_out</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>从 internT 转换字符串为 externT 转换字符串，如在写入文件时<br />
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<span class="t-mark">(<code>std::codecvt<InternT,ExternT,State></code> 的虚受保护成员函数)</span></td>
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<div class="visualClear"></div>
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