136 lines
11 KiB
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136 lines
11 KiB
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<title>std::current_exception</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_error_current_exception 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>current_exception</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-error.html">error</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-exception.html"><exception></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-error-exception_ptr.html"><span class="kw776">std::<span class="me2">exception_ptr</span></span></a> current_exception<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>若在当前异常处理（典型地在 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">catch</span></span></span> 子句中）中调用，则捕获当前异常对象，并创建一个保有该异常对象复制或到该异常对象引用的 <span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</a></span> （依赖于实现）。被引用对象保持合法，只要至少要有一个 <code>exception_ptr</code> 对象引用它。</p>
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<p>若此函数的实现要求对 <span class="t-c"><span class="mw-geshi cpp source-cpp">new</span></span> 的调用且调用失败，则返回地指针将保有到一个 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 实例的引用。</p>
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<p>若此函数的实现要求复制被捕获异常对象，且其复制构造函数抛出异常，则返回的指针将保有到被抛出异常的引用。若该被抛出遗产对象的复制构造函数亦抛出，则返回的指针可能保有到 <span class="t-lc"><a href="cpp-error-bad_exception.html">std::bad_exception</a></span> 实例的引用，以打断无尽循环。</p>
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<p>若函数在无被处理异常时调用，则返回空的 <span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</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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<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>保有到异常对象引用，或异常对象副本，或指向 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 实例，或指向 <span class="t-lc"><a href="cpp-error-bad_exception.html">std::bad_exception</a></span> 实例的 <span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</a></span> 的实例。</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-template-editlink" style=""></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 <string></span>
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<span class="co2">#include <exception></span>
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<span class="co2">#include <stdexcept></span>
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<span class="kw4">void</span> handle_eptr<span class="br0">(</span><a href="cpp-error-exception_ptr.html"><span class="kw776">std::<span class="me2">exception_ptr</span></span></a> eptr<span class="br0">)</span> <span class="co1">// 按值传递 ok</span>
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<span class="br0">{</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>eptr<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-error-rethrow_exception.html"><span class="kw778">std::<span class="me2">rethrow_exception</span></span></a><span class="br0">(</span>eptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span> <span class="kw1">catch</span><span class="br0">(</span><span class="kw4">const</span> <a href="cpp-error-exception.html"><span class="kw764">std::<span class="me2">exception</span></span></a><span class="sy3">&</span> e<span class="br0">)</span> <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">"Caught exception <span class="es1">\"</span>"</span> <span class="sy1"><<</span> e.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span><span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</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-error-exception_ptr.html"><span class="kw776">std::<span class="me2">exception_ptr</span></span></a> eptr<span class="sy4">;</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="br0">(</span><span class="br0">)</span>.<span class="me1">at</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 这生成一个 std::out_of_range</span>
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<span class="br0">}</span> <span class="kw1">catch</span><span class="br0">(</span>...<span class="br0">)</span> <span class="br0">{</span>
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eptr <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">current_exception</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 捕获</span>
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<span class="br0">}</span>
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handle_eptr<span class="br0">(</span>eptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="co1">// std::out_of_range 的析构函数调用于此，在 ept 析构时</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">Caught exception "basic_string::at"</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-error-exception_ptr.html"><span class="t-lines"><span>exception_ptr</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>用于处理异常对象的共享指针类型<br />
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<span class="t-mark">(typedef)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-error-rethrow_exception.html"><span class="t-lines"><span>rethrow_exception</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>从一个 <span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</a></span> 抛出异常<br />
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<span class="t-mark">(函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-error-make_exception_ptr.html"><span class="t-lines"><span>make_exception_ptr</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>从异常对象创建一个<span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</a></span><br />
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<span class="t-mark">(函数模板)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-error-uncaught_exception.html"><span class="t-lines"><span>uncaught_exception</span><span>uncaught_exceptions</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>检查当前是否正在进行异常处理<br />
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<span class="t-mark">(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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</div>
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</body>
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