101 lines
6.4 KiB
HTML
101 lines
6.4 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::basic_istream<CharT,Traits>::gcount</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_istream_gcount 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::basic_istream<CharT,Traits>::</span>gcount</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-basic_istream.html">basic istream</a></span></div>
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<tbody>
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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"><a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> gcount<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></td>
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<td></td>
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<td></td>
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<td></td>
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<p>返回最近的<a href="cpp-named_req-UnformattedInputFunction.html">无格式输入操作</a>所提取的字符数，或若该数不可表示则返回 <span class="t-lc"><a href="cpp-io-streamsize.html">std::streamsize</a></span> 的最大可表示值。</p>
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<p><code>basic_istream</code> 的下列成员函数更改后继的 <code>gcount()</code> 调用的值：</p>
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<ul>
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<li><a href="cpp-io-basic_istream-basic_istream.html">移动构造函数</a></li>
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<li><span class="t-lc"><a href="cpp-io-basic_ios-swap.html">swap()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-get.html">get()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-getline.html">getline()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-ignore.html">ignore()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-read.html">read()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-readsome.html">readsome()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-operator_gtgt.html">operator>>(basic_streambuf*)</a></span></li>
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</ul>
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<p>下列函数设置 <code>gcount()</code> 为零：</p>
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<ul>
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<li><a href="cpp-io-basic_istream-basic_istream.html">构造函数</a></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-putback.html">putback()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-unget.html">unget()</a></span></li>
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<li><span class="t-lc"><a href="cpp-io-basic_istream-peek.html">peek()</a></span></li>
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</ul>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</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>最近的无格式输入操作所提取的字符数，或若该数不可表示则返回 <span class="t-lc"><a href="cpp-io-streamsize.html">std::streamsize</a></span> 的最大可表示值。</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="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 <sstream></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="kw4">char</span> x<span class="br0">[</span><span class="nu0">20</span><span class="br0">]</span><span class="sy4">;</span>
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<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> stream<span class="br0">(</span><span class="st0">"Hello World"</span><span class="br0">)</span><span class="sy4">;</span>
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stream.<span class="me1">read</span><span class="br0">(</span>x, sizeof x<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">"Characters extracted: "</span> <span class="sy1"><<</span> stream.<span class="me1">gcount</span><span class="br0">(</span><span class="br0">)</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">Characters extracted: 11</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3464">LWG 3464</a></td>
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<td>C++98</td>
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<td>结果溢出时返回值未指定</td>
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<td>返回最大值</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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</body>
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</html>
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