152 lines
12 KiB
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152 lines
12 KiB
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<title>std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>::from_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>from_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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<div><span class="mw-geshi cpp source-cpp">wide_string from_bytes<span class="br0">(</span> <span class="kw4">char</span> byte <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">wide_string from_bytes<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> ptr <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">wide_string from_bytes<span class="br0">(</span> <span class="kw4">const</span> byte_string<span class="sy3">&</span> str <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp">wide_string from_bytes<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> first, <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> last<span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>用构造中时提供的 codecvt 平面，进行多字节到宽转换。</p>
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<p>1) 转换 <code>byte</code> 为 wide_string ，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。</p>
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<p>2) 转换始于 <code>ptr</code> 所指向字符的空终止多字节字符序列为 wide_string 。</p>
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<p>3) 转换窄字符串 <code>str</code> 为 wide_string 。</p>
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<p>4) 转换窄多字节字符序列 <code>[first, last)</code> 为 wide_string 。</p>
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<p>所有情况下，转换以初始迁移状态起始，除非提供了非初始起始状态给此 <code>wstring_convert</code> 的构造函数。记忆转换的字符数和转换状态的终值，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>含有多字节到宽转换结果的 <code>wide_string</code> 对象。若转换失败，且有用户提供的宽错误字符串提供给此 <code>wstring_convert</code> 的构造函数，则返回该宽错误字符串。</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> 不以用户提供的宽错误字符串构造，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="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="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> utf8 <span class="sy1">=</span> u8<span class="st0">"z<span class="es3">\u00df</span><span class="es3">\u6c34</span><span class="es4">\U0001d10b</span>"</span><span class="sy4">;</span> <span class="co1">// 或 u8"zß水𝄋"</span>
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<span class="co1">// 或 "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";</span>
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<span class="co1">// UTF-8 / UTF-16 标准转换平面</span>
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<a href="cpp-string-basic_string.html"><span class="kw1234">std::<span class="me2">u16string</span></span></a> utf16 <span class="sy1">=</span> <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_utf16.html"><span class="kw1985">std::<span class="me2">codecvt_utf8_utf16</span></span></a><span class="sy1"><</span><span class="kw4">char16_t</span><span class="sy1">></span>, <span class="kw4">char16_t</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span>.<span class="me1">from_bytes</span><span class="br0">(</span>utf8.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span><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">"UTF16 conversion produced "</span> <span class="sy1"><<</span> utf16.<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="kw1">for</span> <span class="br0">(</span><span class="kw4">char16_t</span> c <span class="sy4">:</span> utf16<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="co1">// UTF-8 / UTF-32 标准转换平面</span>
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<a href="cpp-string-basic_string.html"><span class="kw1236">std::<span class="me2">u32string</span></span></a> utf32 <span class="sy1">=</span> <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">char32_t</span><span class="sy1">></span>, <span class="kw4">char32_t</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span>.<span class="me1">from_bytes</span><span class="br0">(</span>utf8<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">"UTF32 conversion produced "</span> <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> utf32.<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="kw1">for</span> <span class="br0">(</span><span class="kw4">char32_t</span> c <span class="sy4">:</span> utf32<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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<p>输出：</p>
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<div class="text source-text">
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<pre class="de1">UTF16 conversion produced 5 code units:
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0x7a
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0xdf
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0x6c34
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0xd834
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0xdd0b
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UTF32 conversion produced 4 code units:
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0x7a
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0xdf
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0x6c34
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0x1d10b</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-locale-wstring_convert-to_bytes.html"><span class="t-lines"><span>to_bytes</span></span></a></div>
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</div>
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<td>转换宽字符串为字符串<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-mbsrtowcs.html"><span class="t-lines"><span>mbsrtowcs</span></span></a></div>
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</div>
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</td>
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<td>给定状态，转换窄多字节字符串到宽字符串<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-in.html"><span class="t-lines"><span>do_in</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 externT 转换字符串为 internT ，如在从文件读取时<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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