144 lines
15 KiB
HTML
144 lines
15 KiB
HTML
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<title>std::c16rtomb</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_multibyte_c16rtomb 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::</span>c16rtomb</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-multibyte.html">multibyte</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cuchar.html"><cuchar></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> c16rtomb<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> s, <span class="kw4">char16_t</span> c16, <a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a><span class="sy2">*</span> ps <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>从变长 16 位宽字符表示（典型地为 UTF-16 ）转换单个编码点到其窄多字节字符表示。</p>
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<p>若 <code>s</code> 不是空指针且 <code>c16</code> 是合法的编码点变长编码中的最后一个 16 位编码单元，则函数确定存储该编码点所需的字节数（包含任何迁移序列，并考虑当前多字节转换状态 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> ），并存储多字节表示于首元素为 <code>s</code> 所指向的字符数组，若必要则更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 。此函数最能写入 <span class="t-c"><span class="mw-geshi cpp source-cpp">MB_CUR_MAX</span></span> 个字节。</p>
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<p>若 <code>s</code> 是空指针，则调用等价于对于某内部缓冲区 <code>buf</code> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">c16rtomb</span><span class="br0">(</span>buf, u<span class="st0">'<span class="es5">\0</span>'</span>, ps<span class="br0">)</span></span></span> 。</p>
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<p>若 <code>c16</code> 是空宽字符 <span class="t-c"><span class="mw-geshi cpp source-cpp">u<span class="st0">'<span class="es5">\0</span>'</span></span></span> ，则存储空字节，前附恢复到初始迁移状态所需的任何迁移序列，并更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 以表示初始迁移状态。</p>
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<p>若 <code>c16</code> 不是宽字符的 16 位表示中最终编码单元，则不写入 <code>s</code> 所指向的数组，只更新 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 。</p>
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<p>此函数所用的宽字符编码为当前活跃的 C 本地环境所指定。</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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<td>s</td>
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<td>-</td>
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<td>指向将存储多字节字符的窄字符数组的指针</td>
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<td>c16</td>
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<td>-</td>
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<td>要转换的 16 位宽字符</td>
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<tr class="t-par">
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<td>ps</td>
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<td>-</td>
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<td>指向转译多字节字符串时所用转换状态对象的指针</td>
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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>成功时，返回写入首元素为 <code>s</code> 所指向的字符数组的字节数（包含任何迁移序列）。此值可以是 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，例如在处理多 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char16_t</span></span></span> 单元序列的前导 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char16_t</span></span></span> 单元时（在处理 UTF-16 代理对中的前导代理时出现）。</p>
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<p>失败时（若 <span class="t-c"><span class="mw-geshi cpp source-cpp">c16</span></span> 不是合法的 16 位编码单元），则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> ，并存储 <span class="t-lc"><a href="cpp-error-errno_macros.html">EILSEQ</a></span> 于 <span class="t-lc"><a href="cpp-error-errno.html">errno</a></span> ，把 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>ps</span></span> 置于未指定状态。</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>C++ 标准将此函数的语义委派到 C 标准。在 C11 刚发布时，不同于转换变宽多字节（如 UTF-8 ）到变宽 16 位（如 UTF-16 ）编码的 <span class="t-lc"><a href="cpp-string-multibyte-mbrtoc16.html">std::mbrtoc16</a></span> ，此函数只能转换单个单元的 16 位编码，这表示尽管此函数的原目的如此，它仍不能转换 UTF-16 到 UTF-8 。这为 C11 后的缺陷报告 <a rel="nofollow" class="external text" href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2059.htm#dr_488">DR488</a> 所更正。</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>注意：此示例假设应用缺陷报告 488 的修复</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 <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <string_view></span>
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<span class="co2">#include <clocale></span>
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<span class="co2">#include <cuchar></span>
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<span class="co2">#include <climits></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-locale-setlocale.html"><span class="kw1989">std::<span class="me2">setlocale</span></span></a><span class="br0">(</span><a href="cpp-locale-LC_categories.html"><span class="kw1992">LC_ALL</span></a>, <span class="st0">"en_US.utf8"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string_view.html"><span class="kw1251">std::<span class="me2">u16string_view</span></span></a> strv <span class="sy1">=</span> u<span class="st0">"zß水🍌"</span><span class="sy4">;</span> <span class="co1">// 或 z\u00df\u6c34\U0001F34C</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Processing "</span> <span class="sy1"><<</span> strv.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" UTF-16 code units: [ "</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">char16_t</span> c <span class="sy4">:</span> strv<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-showbase.html"><span class="kw1765">std::<span class="me2">showbase</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-hex.html"><span class="kw1781">std::<span class="me2">hex</span></span></a> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"]<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<a href="cpp-string-multibyte-mbstate_t.html"><span class="kw1178">std::<span class="me2">mbstate_t</span></span></a> state<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">char</span> out<span class="br0">[</span><a href="cpp-types-climits.html"><span class="kw388">MB_LEN_MAX</span></a><span class="br0">]</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">char16_t</span> c <span class="sy4">:</span> strv<span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> rc <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">c16rtomb</span><span class="br0">(</span>out, c, <span class="sy3">&</span>state<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">" converted to [ "</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span>rc <span class="sy3">!</span><span class="sy1">=</span> <span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">)</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span> c8 <span class="sy4">:</span> <a href="cpp-string-basic_string_view.html"><span class="kw1247">std::<span class="me2">string_view</span></span></a><span class="br0">{</span>out, rc<span class="br0">}</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="sy2">+</span>c8 <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</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="br0">}</span></pre></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">Processing 5 UTF-16 code units: [ 0x7a 0xdf 0x6c34 0xd83c 0xdf4c ]
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0x7a converted to [ 0x7a ]
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0xdf converted to [ 0xc3 0x9f ]
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0x6c34 converted to [ 0xe6 0xb0 0xb4 ]
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0xd83c converted to [ ]
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0xdf4c converted to [ 0xf0 0x9f 0x8d 0x8c ]</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 class="t-dsc-member-div">
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<div><a href="cpp-string-multibyte-mbrtoc16.html"><span class="t-lines"><span>mbrtoc16</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>转换窄多字节字符为 UTF-16 编码<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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