203 lines
14 KiB
HTML
203 lines
14 KiB
HTML
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<title>std::basic_ostream<CharT,Traits>::sentry</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_ostream_sentry 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_ostream<CharT,Traits>::</span>sentry</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_ostream.html">basic ostream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> sentry<span class="sy4">;</span></span></div>
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<p>类 <code>basic_ostream::sentry</code> 的对象在 <span class="t-lc"><a href="cpp-io-basic_ostream.html">std::basic_ostream</a></span> 的每个进行输出（有格式与无格式）的成员函数起始的局部作用域中构造。其构造函数准备输出流：检查流是否已在失败状态，冲入所 tie() 的输出流，并且若需要则进行其他实现定义的任务。实现定义的清理，还有若有必要的输出流冲入，在析构函数中进行，从而保证若输出中抛出异常则得到执行。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<div><strong class="selflink"><span class="t-lines"><span>(构造函数)</span></span></strong></div>
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<td>构造 sentry 对象。所有准备任务都在此完成。<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><strong class="selflink"><span class="t-lines"><span>(析构函数)</span></span></strong></div>
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</td>
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<td>在有格式输入后或异常后终止化流对象，若有必要<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><span class="t-lines"><span>operator=</span></span></div>
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<td>赋值运算符被删除<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div><strong class="selflink"><span class="t-lines"><span>operator bool</span></span></strong></div>
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</td>
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<td>检查流对象的准备是否成功<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<h2><span class="mw-headline" id="std::basic_ostream::sentry::sentry"><span style="font-size:0.7em; line-height:130%">std::basic_ostream::sentry::</span>sentry</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> sentry<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 <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>为有格式输出准备流。</p>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 则返回。否则若 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">tie</span><span class="br0">(</span><span class="br0">)</span></span></span> 不是空指针，则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">tie</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>flush<span class="br0">(</span><span class="br0">)</span></span></span> 以令输出序列同步于外部流。在准备中，构造函数可能调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>failbit<span class="br0">)</span></span></span> （它可能抛出 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">std::ios_base::failure</a></span> ）。</p>
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<p>若在准备完成后 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="kw2">true</span></span></span> ，则任何对 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator <span class="kw4">bool</span></span></span> 的后继调用都会返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></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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<td>os</td>
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<td>-</td>
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<td>要准备的输出流</td>
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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>若文件尾条件出现则为 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">std::ios_base::failure</a></span>。</p>
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<p><br /></p>
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<h2><span class="mw-headline" id="std::basic_ostream::sentry::.7Esentry"><span style="font-size:0.7em; line-height:130%">std::basic_ostream::sentry::</span>~sentry</span></h2>
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<div><span class="mw-geshi cpp source-cpp">~sentry<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>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> <a href="cpp-io-ios_base-fmtflags.html"><span class="kw1695">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">unitbuf</span></span></a><span class="br0">)</span> <span class="sy3">&&</span> <span class="sy3">!</span><a href="cpp-error-exception-uncaught_exception.html"><span class="kw775">std::<span class="me2">uncaught_exception</span></span></a><span class="br0">(</span><span class="br0">)</span> <span class="sy3">&&</span> os.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，则调用 <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>pubsync<span class="br0">(</span><span class="br0">)</span></span></span> 。若该函数返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> ，则于 <span class="t-c"><span class="mw-geshi cpp source-cpp">os.<span class="me1">rdstate</span><span class="br0">(</span><span class="br0">)</span></span></span> 中设置 <span class="t-c"><span class="mw-geshi cpp source-cpp">badbit</span></span> ，而不传播异常。</p>
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<p><br /></p>
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<h2><span class="mw-headline" id="std::basic_ostream::sentry::operator_bool"><span style="font-size:0.7em; line-height:130%">std::basic_ostream::sentry::</span>operator bool</span></h2>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> operator <span class="kw4">bool</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<p>检查输出流的准备是否成功。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0_2">参数</span></h3>
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<p>（无）</p>
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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>若输出流的准备成功则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</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 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="kw1">struct</span> Foo
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<span class="br0">{</span>
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<span class="kw4">char</span> n<span class="br0">[</span><span class="nu0">6</span><span class="br0">]</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-basic_ostream.html"><span class="kw1728">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> operator<span class="sy1"><<</span><span class="br0">(</span><a href="cpp-io-basic_ostream.html"><span class="kw1728">std::<span class="me2">ostream</span></span></a><span class="sy3">&</span> os, Foo<span class="sy3">&</span> f<span class="br0">)</span>
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<span class="br0">{</span>
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std<span class="sy4">::</span><span class="me2">ostream</span><span class="sy4">::</span><span class="me2">sentry</span> s<span class="br0">(</span>os<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>s<span class="br0">)</span> <span class="br0">{</span>
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os.<span class="me1">write</span><span class="br0">(</span>f.<span class="me1">n</span>, <span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> os<span class="sy4">;</span>
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<span class="br0">}</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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Foo f <span class="sy1">=</span> <span class="br0">{</span> <span class="st0">"abcde"</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> f <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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<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">abcde</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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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_ostream-operator_ltlt.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>插入带格式数据<br />
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<span class="t-mark">(公开成员函数)</span></td>
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