127 lines
10 KiB
HTML
127 lines
10 KiB
HTML
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<title>std::basic_istream<CharT,Traits>::ignore</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_istream_ignore 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::basic_istream<CharT,Traits>::</span>ignore</h1>
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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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<div><span class="mw-geshi cpp source-cpp">basic_istream<span class="sy3">&</span> ignore<span class="br0">(</span> <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> count <span class="sy1">=</span> <span class="nu0">1</span>, int_type delim <span class="sy1">=</span> Traits<span class="sy4">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td></td>
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<td></td>
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<p>从输入流释出并舍弃字符，直至并包含 <code>delim</code> 。</p>
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<p><code>ignore</code> 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> 。构造并检查 sentry 对象后，它从流释出并舍弃字符，直至出现任一下列条件：</p>
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<ul>
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<li>已释出 <code>count</code> 个字符。在 <code>count</code> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span><a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a><span class="sy1">></span><span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span></span></span> 的特殊情况下禁用此测试。</li>
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</ul>
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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> 。</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> 为 <code>delim</code> ，以 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eq_int_type</span><span class="br0">(</span>Traits<span class="sy4">::</span><span class="me2">to_int_type</span><span class="br0">(</span>c<span class="br0">)</span>, delim<span class="br0">)</span></span></span> 确定。释出并舍弃分隔符。若 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span></span></span> 为则禁用此测试。</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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<table class="t-par-begin">
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<td>count</td>
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<td>-</td>
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<td>要释出的字符数</td>
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</tr>
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<tr class="t-par">
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<td>delim</td>
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<td>-</td>
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<td>释出所止于的分隔字符。亦释出之。</td>
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</tr>
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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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></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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<div class="t-template-editlink" style=""></div>
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若出现错误（错误状态标志不是 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">goodbit</a></span> ）并且设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> 为对该状态抛出则为 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">failure</a></span> 。
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<p>若内部操作抛出异常，则捕获它并设置 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">badbit</a></span> 。若对 <code>badbit</code> 设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> ，则重抛该异常。</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>下列代码用 <code>ignore</code> 跳过非数值输入：</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 <sstream></span>
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<span class="co2">#include <limits></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> input<span class="br0">(</span><span class="st0">"1<span class="es1">\n</span>"</span>
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<span class="st0">"some non-numeric input<span class="es1">\n</span>"</span>
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<span class="st0">"2<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="sy4">;;</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">int</span> n<span class="sy4">;</span>
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input <span class="sy1">>></span> n<span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>input.<span class="me1">eof</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">||</span> input.<span class="me1">bad</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span>input.<span class="me1">fail</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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input.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 反设置 failbit</span>
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input.<span class="me1">ignore</span><span class="br0">(</span><a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span><a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a><span class="sy1">></span><span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span>, <span class="st0">'<span class="es1">\n</span>'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 跳过坏输入</span>
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<span class="br0">}</span> <span class="kw1">else</span> <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> n <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>
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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">1
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2</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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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_istream-get.html"><span class="t-lines"><span>get</span></span></a></div>
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</div>
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</td>
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<td>从流中读并取走（移除类似指针向下一个元素移动）一个字符<br />
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<span class="t-mark">(公开成员函数)</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-basic_istream-getline.html"><span class="t-lines"><span>getline</span></span></a></div>
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</div>
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</td>
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<td>一直读并取走字符，直至找到给定字符<br />
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<span class="t-mark">(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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