134 lines
12 KiB
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134 lines
12 KiB
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<title>std::cerr, std::wcerr</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>cerr, <span style="font-size:0.7em; line-height:130%">std::</span>wcerr</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-io.html">io</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-iostream.html"><iostream></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">extern</span> <a href="cpp-io-basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a> cerr<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"><span class="kw4">extern</span> <a href="cpp-io-basic_ostream.html"><span class="kw1743">std::<span class="me2">wostream</span></span></a> wcerr<span class="sy4">;</span></span></div>
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<p>全局对象 <code>std::cerr</code> 和 <code>std::wcerr</code> 控制到实现定义类型（分别导出自 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> 和 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::wstreambuf</a></span> ）的流缓冲，与标准 C 错误输出流 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span> 关联。</p>
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<p>保证这些对象在构造首个 <span class="t-lc"><a href="cpp-io-ios_base-Init.html">std::ios_base::Init</a></span> 类型对象之前或期间得到初始化，而且可用于带<a href="cpp-language-initialization.html#.E9.9D.9E.E5.B1.80.E9.83.A8.E5.8F.98.E9.87.8F">有序初始化</a>的静态对象的构造函数和析构函数（只要在定义对象前包含 <code><iostream></code> ）。</p>
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<p>除非发出 <span class="t-c"><span class="mw-geshi cpp source-cpp">sync_with_stdio<span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span></span></span> ，有格式和无格式输出从多个线程访问这些对象是安全的。</p>
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<p>一旦初始化，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">cerr</span>.<span class="me1">flags</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">&</span> unitbuf<span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">0</span></span></span> （ <code>wcerr</code> 也一样），这表示任何发送给这些流对象的输出都被立即冲入到 OS （通过 <span class="t-lc"><a href="cpp-io-basic_ostream-sentry.html">std::basic_ostream::sentry</a></span> 的析构函数）。</p>
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<p>另外， <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">cerr</span>.<span class="me1">tie</span><span class="br0">(</span><span class="br0">)</span></span></span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">&</span><a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a></span></span> （对 <code>wcerr</code> 和 <code>wcout</code> 相同），这表示任何 <span class="t-lc"><strong class="selflink">std::cerr</strong></span> 上的输出首先执行 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">flush</span><span class="br0">(</span><span class="br0">)</span></span></span> （通过 <span class="t-lc"><a href="cpp-io-basic_ostream-sentry.html">std::basic_ostream::sentry</a></span> 的构造函数）。<span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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>名称中的 'c' 指代“字符”（ <a rel="nofollow" class="external text" href="http://www.stroustrup.com/bs_faq2.html#cout">stroustrup.com FAQ</a> ）； <code>cerr</code> 表示“字符错误（流）”而 <code>wcerr</code> 表示“宽字符错误（流）”。</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>通过 cerr 输出到 stderr ，冲入 cout 上的待处理输出，而通过 clog 输出到 stderr 不会。</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 <thread></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <chrono></span>
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<span class="kw4">void</span> f<span class="br0">(</span><span class="br0">)</span>
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<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="st0">"Output from thread..."</span><span class="sy4">;</span>
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<a href="cpp-thread-sleep_for.html"><span class="kw2147">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</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="st0">"...thread calls flush()"</span> <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1789">std::<span class="me2">endl</span></span></a><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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<a href="cpp-thread-thread.html"><span class="kw2144">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span>f<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-thread-sleep_for.html"><span class="kw2147">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="cpp-chrono-duration.html"><span class="kw997">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-clog.html"><span class="kw1760">std::<span class="me2">clog</span></span></a> <span class="sy1"><<</span> <span class="st0">"This output from main is not tie()'d to cout<span class="es1">\n</span>"</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">cerr</span> <span class="sy1"><<</span> <span class="st0">"This output is tie()'d to cout<span class="es1">\n</span>"</span><span class="sy4">;</span>
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t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</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">This output from main is not tie()'d to cout
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Output from thread...This output is tie()'d to cout
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...thread calls flush()</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-ios_base-Init.html"><span class="t-lines"><span>Init</span></span></a></div>
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</div>
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</td>
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<td>初始化标准流对象<br />
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<span class="t-mark">(<code>std::ios_base</code> 的公开成员类)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-clog.html"><span class="t-lines"><span>clog</span><span>wclog</span></span></a></div>
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</div>
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<td>写入到标准 C 错误流 <span class="t-lc"><a href="cpp-io-c.html">stderr</a></span><br />
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<span class="t-mark">(全局对象)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-cout.html"><span class="t-lines"><span>cout</span><span>wcout</span></span></a></div>
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</div>
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<td>写入到标准 C 输出流 <span class="t-lc"><a href="cpp-io-c.html">stdout</a></span><br />
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<span class="t-mark">(全局对象)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-std_streams.html"><span class="t-lines"><span>stdin</span><span>stdout</span><span>stderr</span></span></a></div>
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</div>
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</td>
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<td>与输入流关联到 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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与输出流关联的 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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与错误输出流关联的 <span class="t-c"><span class="mw-geshi cpp source-cpp">FILE<span class="sy2">*</span></span></span> 类型表达式<br />
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<span class="t-mark">(宏常量)</span></td>
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