162 lines
17 KiB
HTML
162 lines
17 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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<title>std::getline</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_basic_string_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::</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-string.html">string</a>‎ | <a href="cpp-string-basic_string.html">basic string</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-string.html"><string></a></code></div>
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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="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> getline<span class="br0">(</span> <a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> input,<br />
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<a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT,Traits,Allocator<span class="sy1">></span><span class="sy3">&</span> str,<br /></p>
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CharT delim <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(1)</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="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> getline<span class="br0">(</span> <a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&&</span> input,<br />
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<a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT,Traits,Allocator<span class="sy1">></span><span class="sy3">&</span> str,<br /></p>
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CharT delim <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> getline<span class="br0">(</span> <a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> input,<br /></p>
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<a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT,Traits,Allocator<span class="sy1">></span><span class="sy3">&</span> str <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(2)</td>
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<td class="t-dcl-nopad"></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="kw1">class</span> Allocator <span class="sy1">></span><br /></span>
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<p><a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> getline<span class="br0">(</span> <a href="cpp-io-basic_istream.html"><span class="kw1712">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&&</span> input,<br /></p>
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<a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT,Traits,Allocator<span class="sy1">></span><span class="sy3">&</span> str <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p><code>getline</code> 从输入流读取字符并将它们放进 string ：</p>
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<div class="t-li1"><span class="t-li">1)</span> 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> ，除了不影响 <code>input.gcount()</code> 。构造并检查 sentry 对象后，进行下列操作：</div>
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<div class="t-li2"><span class="t-li">1)</span> 调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">erase</span><span class="br0">(</span><span class="br0">)</span></span></span></div>
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<div class="t-li2"><span class="t-li">2)</span> 从 <code>input</code> 释出字符并后附它们到 <code>str</code> ，直至发生下列条件之一（按顺序检查）：</div>
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<div class="t-li3"><span class="t-li">a)</span> <code>input</code> 上的文件尾条件，该情况下， <code>getline</code> 设置 <a href="cpp-io-ios_base-iostate.html"><tt>eofbit</tt></a> 。</div>
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<div class="t-li3"><span class="t-li">b)</span> 下个可用输入字符是 <code>delim</code> ，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> 测试，该情况下从 <code>input</code> 释出分隔字符，但不后附它到 <code>str</code> 。</div>
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<div class="t-li3"><span class="t-li">c)</span> 已经存储 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">max_size</span><span class="br0">(</span><span class="br0">)</span></span></span> 个字符，该情况下 <code>getline</code> 设置 <a href="cpp-io-ios_base-iostate.html"><tt>failbit</tt></a> 并返回。</div>
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<div class="t-li2"><span class="t-li">3)</span> 若因任何原因（不是舍弃的分隔符）没有释出字符，则 <code>getline</code> 设置 <a href="cpp-io-ios_base-iostate.html"><tt>failbit</tt></a> 并返回。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-c"><span class="mw-geshi cpp source-cpp">getline<span class="br0">(</span>input, str, input.<span class="me1">widen</span><span class="br0">(</span><span class="st0">'<span class="es1">\n</span>'</span><span class="br0">)</span><span class="br0">)</span></span></span> ，即默认分隔符是换行符。</div>
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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>input</td>
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<td>-</td>
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<td>获取数据来源的流</td>
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</tr>
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<tr class="t-par">
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<td>str</td>
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<td>-</td>
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<td>放置数据的目标 string</td>
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</tr>
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<td>delim</td>
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<td>-</td>
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<td>分隔字符</td>
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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>input</code></p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>消耗空白符分隔的输入（例如 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> n<span class="sy4">;</span> <a href="cpp-io-cin.html"><span class="kw1755">std::<span class="me2">cin</span></span></a> <span class="sy1">>></span> n<span class="sy4">;</span></span></span> ）时，任何后随的空白符，包括换行符都会被留在流中。然后当切换到面向行的输入时，以 <code>getline</code> 取得的首行只会是该空白符。多数情况下这是不想要的行为，可能的解法包括：</p>
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<ul>
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<li>对 <code>getline</code> 的显式的额外初始调用</li>
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<li>以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-cin.html"><span class="kw1755">std::<span class="me2">cin</span></span></a> <span class="sy1">>></span> <a href="cpp-io-manip-ws.html"><span class="kw1787">std::<span class="me2">ws</span></span></a></span></span> 移除额外的空白符</li>
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<li>以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-cin.html"><span class="kw1755">std::<span class="me2">cin</span></span></a>.<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="kw1803">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></span> 忽略输入行上剩下的全部字符</li>
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</ul>
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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>下列代码演示如何用 <code>getline</code> 函数读取用户输入以及如何逐行处理文件。</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 <string></span>
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<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="co1">// 问候用户</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> name<span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"What is your name? "</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">getline</span><span class="br0">(</span><a href="cpp-io-cin.html"><span class="kw1755">std::<span class="me2">cin</span></span></a>, name<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Hello "</span> <span class="sy1"><<</span> name <span class="sy1"><<</span> <span class="st0">", nice to meet you.<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="co1">// 逐行读文件</span>
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<a href="cpp-io-basic_istringstream.html"><span class="kw1734">std::<span class="me2">istringstream</span></span></a> input<span class="sy4">;</span>
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input.<span class="me1">str</span><span class="br0">(</span><span class="st0">"1<span class="es1">\n</span>2<span class="es1">\n</span>3<span class="es1">\n</span>4<span class="es1">\n</span>5<span class="es1">\n</span>6<span class="es1">\n</span>7<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> sum <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> line<span class="sy4">;</span> std<span class="sy4">::</span><span class="me2">getline</span><span class="br0">(</span>input, line<span class="br0">)</span><span class="sy4">;</span> <span class="br0">)</span> <span class="br0">{</span>
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sum <span class="sy2">+</span><span class="sy1">=</span> <a href="cpp-string-basic_string-stol.html"><span class="kw1256">std::<span class="me2">stoi</span></span></a><span class="br0">(</span>line<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\n</span>The sum is: "</span> <span class="sy1"><<</span> sum <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></pre></div>
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</div>
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<p>可能的输出：</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">What is your name? John Q. Public
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Hello John Q. Public, nice to meet you.
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The sum is 28</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-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">(<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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