89 lines
5.8 KiB
HTML
89 lines
5.8 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::ungetwc</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_c_ungetwc 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>ungetwc</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-io.html">io</a>‎ | <a href="cpp-io-c.html">c</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-cwchar.html"><cwchar></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>
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<tr class="t-dcl">
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<td class="t-dcl-nopad">
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<div><span class="mw-geshi cpp source-cpp">wint_t ungetwc<span class="br0">(</span> wint_t ch, <a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span> stream <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></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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</tr>
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</tbody>
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</table>
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<p>若 <code>ch</code> 不等于 <span class="t-lc">WEOF</span> ，则推入宽字符 <code>ch</code> 到与流 <code>stream</code> 关联的输入缓冲区，方式满足从 <code>stream</code> 的后继读取操作将取得该宽字符。不修改与流关联的外部设备。</p>
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<p>流重寻位操作 <span class="t-lc"><a href="cpp-io-c-fseek.html">std::fseek</a></span> 、 <span class="t-lc"><a href="cpp-io-c-fsetpos.html">std::fsetpos</a></span> 和 <span class="t-lc"><a href="cpp-io-c-rewind.html">std::rewind</a></span> 弃去 <code>ungetwc</code> 的效果。</p>
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<p>若调用 <code>ungetwc</code> 多于一次，而无中间读取或重寻位，则可能失败（换言之，保证大小为 1 的回放缓冲区，但任何更大的缓冲区是实现定义的）。若成功进行多次 <code>ungetwc</code> ，则读取操作以 <code>ungetwc</code> 的逆序取得回放的宽字符。</p>
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<p>若 <code>ch</code> 等于 <span class="t-lc">WEOF</span> ，则操作失败而不影响流。</p>
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<p>对 <code>ungetwc</code> 的成功调用清除文件尾状态标志 <span class="t-lc">feof</span> 。</p>
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<p>在流（无论文本还是二进制）上对 <code>ungetwc</code> 的成功调用以未指定方式修改流位置指示器，但保证在以读取操作取得所有回放的宽字符后，流位置指示器等于其在 <code>ungetwc</code> 之前的值。</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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<table class="t-par-begin">
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<tr class="t-par">
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<td>ch</td>
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<td>-</td>
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<td>要推入输入流缓冲区的宽字符</td>
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</tr>
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<tr class="t-par">
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<td>stream</td>
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<td>-</td>
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<td>要回放宽字符到的文件流</td>
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</tr>
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</table>
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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 <code>ch</code> 。</p>
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<p>失败时返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">WEOF</span></span> ，而给定的流保持不变。</p>
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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-io-c-ungetc.html"><span class="t-lines"><span>ungetc</span></span></a></div>
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</div>
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</td>
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<td>把字符放回文件流<br />
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<span class="t-mark">(函数)</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-io-c-fgetwc.html"><span class="t-lines"><span>fgetwc</span><span>getwc</span></span></a></div>
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</div>
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</td>
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<td>从文件流获取宽字符<br />
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<span class="t-mark">(函数)</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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