181 lines
16 KiB
HTML
181 lines
16 KiB
HTML
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<title>std::promise<R>::set_value</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::promise<R>::</span>set_value</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-thread.html">thread</a>‎ | <a href="cpp-thread-promise.html">promise</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> set_value<span class="br0">(</span> <span class="kw4">const</span> R<span class="sy3">&</span> value <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(仅为泛型 <code>promise</code> 模板的成员)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> set_value<span class="br0">(</span> R<span class="sy3">&&</span> value <span class="br0">)</span><span class="sy4">;</span></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><br />
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<span class="t-mark">(仅为泛型 <code>promise</code> 模板的成员)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> set_value<span class="br0">(</span> R<span class="sy3">&</span> value <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(仅为 <code>promise<R&></code> 模板特化的成员)</span></td>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> set_value<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span><br />
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<span class="t-mark">(仅为 <code>promise<void></code> 模板特化的成员)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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<div class="t-li1"><span class="t-li">1-3)</span> 原子地存储 <code>value</code> 到共享状态，并令状态就绪。</div>
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<div class="t-li1"><span class="t-li">4)</span> 使状态就绪。</div>
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<p><code>set_value</code> 、 <span class="t-lc"><a href="cpp-thread-promise-set_exception.html">set_exception</a></span> 、 <span class="t-lc"><a href="cpp-thread-promise-set_value_at_thread_exit.html">set_value_at_thread_exit</a></span> 和 <span class="t-lc"><a href="cpp-thread-promise-set_exception_at_thread_exit.html">set_exception_at_thread_exit</a></span> 的操作表现类似。在更新 <code>promise</code> 对象时获得单个与 <code>promise</code> 对象关联的互斥。</p>
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<p>若无共享状态或共享状态已存储值或异常，则抛出异常。</p>
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<p>对此函数的调用和对 <span class="t-lc"><a href="cpp-thread-promise-get_future.html">get_future</a></span> 的调用不会造成数据竞争（但它们不需要彼此同步）。</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>value</td>
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<td>-</td>
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<td>要存储于共享状态的值</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>（无）</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>遇到下列条件时为 <span class="t-lc"><a href="cpp-thread-future_error.html">std::future_error</a></span> ：</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 无共享状态。设置 error_category 为 <a href="cpp-thread-future_errc.html"><tt>no_state</tt></a> 。</li>
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</ul>
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<ul>
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<li>共享状态已存储值或异常。设置 error_category 为 <a href="cpp-thread-future_errc.html"><tt>promise_already_satisfied</tt></a> 。</li>
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</ul>
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<p>另外；</p>
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<div class="t-li1"><span class="t-li">1, 3)</span> <code>value</code> 的复制构造函数所抛的任何异常</div>
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<div class="t-li1"><span class="t-li">2)</span> <code>value</code> 的移动构造函数所抛的任何异常</div>
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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>这显示能如何将 <code>promise<void></code> 用于在线程间发信号。</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 <future></span>
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<span class="co2">#include <cctype></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <algorithm></span>
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<span class="co2">#include <iterator></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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<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> iss_numbers<span class="br0">{</span><span class="st0">"3 4 1 42 23 -23 93 2 -289 93"</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> iss_letters<span class="br0">{</span><span class="st0">" a 23 b,e a2 k k?a;si,ksa c"</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><span class="kw4">int</span><span class="sy1">></span> numbers<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><span class="kw4">char</span><span class="sy1">></span> letters<span class="sy4">;</span>
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<a href="cpp-thread-promise.html"><span class="kw2179">std::<span class="me2">promise</span></span></a><span class="sy1"><</span><span class="kw4">void</span><span class="sy1">></span> numbers_promise, letters_promise<span class="sy4">;</span>
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<span class="kw4">auto</span> numbers_ready <span class="sy1">=</span> numbers_promise.<span class="me1">get_future</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">auto</span> letter_ready <span class="sy1">=</span> letters_promise.<span class="me1">get_future</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-thread-thread.html"><span class="kw2146">std::<span class="me2">thread</span></span></a> value_reader<span class="br0">(</span><span class="br0">[</span><span class="sy3">&</span><span class="br0">]</span>
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<span class="br0">{</span>
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<span class="co1">// I/O 操作。</span>
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<a href="cpp-algorithm-copy.html"><span class="kw1582">std::<span class="me2">copy</span></span></a><span class="br0">(</span><a href="cpp-iterator-istream_iterator.html"><span class="kw668">std::<span class="me2">istream_iterator</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">{</span>iss_numbers<span class="br0">}</span>,
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<a href="cpp-iterator-istream_iterator.html"><span class="kw668">std::<span class="me2">istream_iterator</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span>,
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<a href="cpp-iterator-back_inserter.html"><span class="kw665">std::<span class="me2">back_inserter</span></span></a><span class="br0">(</span>numbers<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 为数字提醒。</span>
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numbers_promise.<span class="me1">set_value</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-copy.html"><span class="kw1583">std::<span class="me2">copy_if</span></span></a><span class="br0">(</span><a href="cpp-iterator-istreambuf_iterator.html"><span class="kw669">std::<span class="me2">istreambuf_iterator</span></span></a><span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span><span class="br0">{</span>iss_letters<span class="br0">}</span>,
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<a href="cpp-iterator-istreambuf_iterator.html"><span class="kw669">std::<span class="me2">istreambuf_iterator</span></span></a><span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span>,
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<a href="cpp-iterator-back_inserter.html"><span class="kw665">std::<span class="me2">back_inserter</span></span></a><span class="br0">(</span>letters<span class="br0">)</span>,
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<span class="sy4">::</span><span class="me2">isalpha</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 为字母提醒。</span>
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letters_promise.<span class="me1">set_value</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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numbers_ready.<span class="me1">wait</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-sort.html"><span class="kw1618">std::<span class="me2">sort</span></span></a><span class="br0">(</span>numbers.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, numbers.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>letter_ready.<span class="me1">wait_for</span><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="sy1">==</span>
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<a href="cpp-thread-future_status.html"><span class="kw2190">std::<span class="me2">future_status</span><span class="sy4">::</span><span class="me2">timeout</span></span></a><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co1">// 在获得字母的同时输出数</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> num <span class="sy4">:</span> numbers<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> num <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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numbers.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">//Numbers were already printed.</span>
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<span class="br0">}</span>
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letter_ready.<span class="me1">wait</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-algorithm-sort.html"><span class="kw1618">std::<span class="me2">sort</span></span></a><span class="br0">(</span>letters.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, letters.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 若已打印数，则不做任何事。</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> num <span class="sy4">:</span> numbers<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> num <span class="sy1"><<</span> <span class="st0">' '</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">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">char</span> let <span class="sy4">:</span> letters<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> let <span class="sy1"><<</span> <span class="st0">' '</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">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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value_reader.<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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</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">-289 -23 1 2 3 4 23 42 93 93
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a a a a b c e i k k k s s</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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<div class="t-dsc-member-div">
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<div><a href="cpp-thread-promise-set_exception.html"><span class="t-lines"><span>set_exception</span></span></a></div>
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</div>
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</td>
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<td>设置结果为指示异常<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 class="visualClear"></div>
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