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<title>operator<<(std::basic_string_view)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_basic_string_view_operator_ltlt skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading">operator<<<span style="font-size:0.7em; line-height:130%">(std::basic_string_view)</span></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_view.html">basic string view</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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<div>定义于头文件 <code><a href="cpp-header-string_view.html"><string_view></a></code></div>
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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 /></span>
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<p><a href="cpp-io-basic_ostream.html"><span class="kw1715">std::<span class="me2">basic_ostream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy3">&</span><br />
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operator<span class="sy1"><<</span><span class="br0">(</span><a href="cpp-io-basic_ostream.html"><span class="kw1715">std::<span class="me2">basic_ostream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span><span class="sy3">&</span> os,<br /></p>
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<a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a> <span class="sy1"><</span>CharT, Traits<span class="sy1">></span> v<span class="br0">)</span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>表现为<a href="cpp-named_req-FormattedOutputFunction.html"><span style="font-style:italic">有格式输出函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FormattedOutputFunction)</span></a> 。构造并检查 sentry 对象后，以下列方式确定输出格式填充：</p>
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<dl>
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<dd>a) 若 <code>v.size()</code> 不小于 <code>os.width()</code> ，则原态使用 <code>[v.begin(), v.end())</code> ；</dd>
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<dd>b) 否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>os.<span class="me1">flags</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">&</span> ios_base<span class="sy4">::</span><span class="me2">adjustfield</span><span class="br0">)</span> <span class="sy1">==</span> ios_base<span class="sy4">::</span><span class="me2">left</span></span></span> ，则将 <code>os.fill()</code> 字符的 <code>os.width()-v.size()</code> 份副本置于字符序列前；</dd>
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<dd>c) 否则，将 <code>os.fill()</code> 字符的 <code>os.width()-v.size()</code> 份副本置于字符序列后。</dd>
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</dl>
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<p>然后如同通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputn<span class="br0">(</span>seq, n<span class="br0">)</span></span></span> ，存储每个来自结果序列（ <code>v</code> 的内容加上填充）于输出流 <code>os</code> ，其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">n<span class="sy1">=</span><a href="cpp-algorithm-max.html"><span class="kw1640">std::<span class="me2">max</span></span></a><span class="br0">(</span>os.<span class="me1">width</span><span class="br0">(</span><span class="br0">)</span>, str.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</p>
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<p>最后，调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">width</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span></span></span> 以取消 <span class="t-lc"><a href="cpp-io-manip-setw.html">std::setw</a></span> 的效果，若存在。</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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<p>若输出时抛异常，则可能抛出 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">std::ios_base::failure</a></span> 。</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>os</td>
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<td>-</td>
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<td>字符输出流</td>
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<tr class="t-par">
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<td>v</td>
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<td>-</td>
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<td>要插入的视图</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>os</code></p>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-operator_ltltgtgt.html"><span class="t-lines"><span>operator<<</span><span>operator>></span></span></a></div>
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</div>
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</td>
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<td>执行字符串的流输入与输出<br />
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<span class="t-mark">(函数模板)</span></td>
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