104 lines
8.0 KiB
HTML
104 lines
8.0 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::ws</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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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_manip_ws 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>ws</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-manip.html">manip</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-istream.html"><istream></a></code></div>
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</td>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> CharT, <span class="kw1">class</span> Traits <span class="sy1">></span><br />
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<a href="cpp-io-basic_istream.html"><span class="kw1713">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> ws<span class="br0">(</span> <a href="cpp-io-basic_istream.html"><span class="kw1713">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy3">&</span> is <span class="br0">)</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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<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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</table>
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<p>从输入流舍弃前导空白符。</p>
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<p>表现为<a href="cpp-named_req-UnformattedInputFunction.html"><span style="font-style:italic">无格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UnformattedInputFunction)</span></a> ，除了不修改 <span class="t-c"><span class="mw-geshi cpp source-cpp">is.<span class="me1">gcount</span><span class="br0">(</span><span class="br0">)</span></span></span> 。在构造并检查 sentry 对象后，从流释出并舍弃字符，直至出现任何下列条件之一：</p>
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<ul>
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<li>输入序列中出现文件尾条件（该情况下函数调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>eofbit<span class="br0">)</span></span></span> 但不设置 <code>failbit</code> ；若调用 <code>ws</code> 前已在 <code>is</code> 上设置 <code>eofbit</code> ，则不适用这条，该情况下 sentry 对象的构造会设置 <code>failbit</code> ）。</li>
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</ul>
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<ul>
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<li>输入序列中下个可用字符 <code>c</code> 不是以 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">isspace</span><span class="br0">(</span>c, is.<span class="me1">getloc</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 确定的空白字符。不释出该非空白字符。</li>
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</ul>
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<p>这是仅为输入的 I/O 操纵符，可用如 <span class="t-c"><span class="mw-geshi cpp source-cpp">in <span class="sy1">>></span> std<span class="sy4">::</span><span class="me2">ws</span></span></span> 的表达式对任何 <span class="t-lc"><a href="cpp-io-basic_istream.html">std::basic_istream</a></span> 类型的 <code>in</code> 调用。</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>is</td>
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<td>-</td>
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<td>到输入流的引用</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><code>is</code> （到释出连续空白符后的流的引用）</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>若在调用前在流上设置了 <code>eofbit</code> ，则 sentry 对象的构造将设置 <code>failbit</code> 。</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 <istream></span>
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<span class="co2">#include <sstream></span>
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<span class="co2">#include <string></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-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> s<span class="br0">(</span><span class="st0">" this is a test"</span><span class="br0">)</span><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> line<span class="sy4">;</span>
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<a href="cpp-string-basic_string-getline.html"><span class="kw1256">std::<span class="me2">getline</span></span></a><span class="br0">(</span>s <span class="sy1">>></span> std<span class="sy4">::</span><span class="me2">ws</span>, line<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">"ws + getline returns: <span class="es1">\"</span>"</span> <span class="sy1"><<</span> line <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span><span class="es1">\n</span>"</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">ws + getline returns: "this is a test"</pre></div>
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</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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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_istream-ignore.html"><span class="t-lines"><span>ignore</span></span></a></div>
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</div>
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</td>
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<td>读且取走并舍弃字符，直至发现给定字符<br />
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<span class="t-mark">(<code>std::basic_istream<CharT,Traits></code> 的公开成员函数)</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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