160 lines
12 KiB
HTML
160 lines
12 KiB
HTML
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<title>std::basic_istream<CharT,Traits>::getline</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_istream_getline 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>getline</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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<div><span class="mw-geshi cpp source-cpp">basic_istream<span class="sy3">&</span> getline<span class="br0">(</span> char_type<span class="sy2">*</span> s, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp">basic_istream<span class="sy3">&</span> getline<span class="br0">(</span> char_type<span class="sy2">*</span> s, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> count, char_type delim <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</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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<p>从流释出字符，直至行尾或指定的分隔符 <code>delim</code> 。</p>
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<p>第一版本等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">getline<span class="br0">(</span>s, count, widen<span class="br0">(</span><span class="st0">'<span class="es1">\n</span>'</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</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> 。构造并检查 sentry 对象后，从 <code>*this</code> 释出字符并存储它们于首元素为 <code>s</code> 所指向的数组的相继位置，直至出现任何下列条件（按出示顺序测试）：</p>
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<ul>
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<li>输入序列中出现文件尾条件（该情况下执行 <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>下个可用字符 <code>c</code> 是以 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eq</span><span class="br0">(</span>c, delim<span class="br0">)</span></span></span> 确定的分隔符。释出该分隔符（不同于 <a href="cpp-io-basic_istream-get.html"><tt>basic_istream::get()</tt></a> ）并计入 <code>gcount()</code> ，但不存储它。</li>
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</ul>
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<ul>
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<li>已经释出 <span class="t-c"><span class="mw-geshi cpp source-cpp">count<span class="sy2">-</span><span class="nu0">1</span></span></span> 个字符（该情况下执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>failbit<span class="br0">)</span></span></span> ）。</li>
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</ul>
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<p>若函数未释出字符（即 <span class="t-c"><span class="mw-geshi cpp source-cpp">count <span class="sy1"><</span> <span class="nu0">1</span></span></span> ），则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>failbit<span class="br0">)</span></span></span> 。</p>
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<p>任何情况下，若 <code>count>0</code> ，则它存储空字符 <code>CharT()</code> 到数组的下个相继位置，并更新 <code>gcount()</code> 。</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>因为条件 #2 在条件 #3 前测试，故准确适合缓冲区的输入行不会触发 failbit 。</p>
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<p>因为终止字符计为释出的字符，故空输入行不触发 failbit 。</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>s</td>
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<td>-</td>
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<td>指向要存储字符到的字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td><code>s</code> 所指向的字符串的大小</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>释出所终止于的分隔字符。释出但不存储它。</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><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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<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 <vector></span>
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<span class="co2">#include <array></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">"abc|def|gh"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">char</span>, <span class="nu0">4</span><span class="sy1">>></span> v<span class="sy4">;</span>
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<span class="co1">// 注意：下列循环在从 getline() 返回的流上的 </span>
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<span class="co1">// std::ios_base::operator bool() 返回 false 时终止</span>
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<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">char</span>, <span class="nu0">4</span><span class="sy1">></span> a<span class="sy4">;</span> input.<span class="me1">getline</span><span class="br0">(</span><span class="sy3">&</span>a<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="nu0">4</span>, <span class="st0">'|'</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">)</span> <span class="br0">{</span>
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v.<span class="me1">push_back</span><span class="br0">(</span>a<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> a <span class="sy4">:</span> v<span class="br0">)</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> <span class="sy3">&</span>a<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <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></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">abc
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def
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gh</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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<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-string-basic_string-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>从 I/O 流读取数据到字符串<br />
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<span class="t-mark">(函数模板)</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-operator_gtgt.html"><span class="t-lines"><span>operator>></span></span></a></div>
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</div>
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</td>
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<td>提取带格式数据<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-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-read.html"><span class="t-lines"><span>read</span></span></a></div>
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</div>
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</td>
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<td>读并取走一块字符<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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</div>
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</div>
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</body>
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</html>
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