146 lines
13 KiB
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146 lines
13 KiB
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<title>std::throw_with_nested</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_error_throw_with_nested 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>throw_with_nested</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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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span><br />
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<span class="br0">[</span><span class="br0">[</span>noreturn<span class="br0">]</span><span class="br0">]</span> <span class="kw4">void</span> throw_with_nested<span class="br0">(</span> T<span class="sy3">&&</span> t <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 是非 final 、非 union 、既非 <span class="t-lc"><a href="cpp-error-nested_exception.html">std::nested_exception</a></span> 亦非从 <span class="t-lc"><a href="cpp-error-nested_exception.html">std::nested_exception</a></span> 派生的类类型，则抛出一个从 <span class="t-lc"><a href="cpp-error-nested_exception.html">std::nested_exception</a></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 两者公开派生的未指定类型的异常，从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span></span></span> 构造。 <code>nested_exception</code> 基类的默认构造函数调用 <span class="t-lc"><a href="cpp-error-current_exception.html">std::current_exception</a></span> ，于一个 <span class="t-lc"><a href="cpp-error-exception_ptr.html">std::exception_ptr</a></span> 捕获当前处理的异常对象，若它存在。</p>
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<p>否则抛出 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span></span></span> 。</p>
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<p>要求 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw628">std::<span class="me2">decay</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span></span></span> 为<a href="cpp-named_req-CopyConstructible.html"><span style="font-style:italic">可复制构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(CopyConstructible)</span></a> 。</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>t</td>
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<td>-</td>
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<td>要抛出的异常对象</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=".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="t-example">
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<p>演示构造并通过 nested_exception 对象递归</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 <iostream></span>
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<span class="co2">#include <stdexcept></span>
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<span class="co2">#include <exception></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <fstream></span>
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<span class="co1">// 打印异常的解释性字符串。若异常内嵌，则递归打印其保有的异常的解释</span>
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<span class="kw4">void</span> print_exception<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="kw4">int</span> level <span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cerr.html"><span class="kw1759">std::<span class="me2">cerr</span></span></a> <span class="sy1"><<</span> <a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="br0">(</span>level, <span class="st0">' '</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"exception: "</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">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<a href="cpp-error-rethrow_if_nested.html"><span class="kw781">std::<span class="me2">rethrow_if_nested</span></span></a><span class="br0">(</span>e<span class="br0">)</span><span class="sy4">;</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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print_exception<span class="br0">(</span>e, level<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</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><span class="br0">}</span>
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<span class="br0">}</span>
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<span class="co1">// 示例函数，捕捉异常并将其包装于 nested_exception</span>
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<span class="kw4">void</span> open_file<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy3">&</span> s<span class="br0">)</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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<a href="cpp-io-basic_ifstream.html"><span class="kw1731">std::<span class="me2">ifstream</span></span></a> file<span class="br0">(</span>s<span class="br0">)</span><span class="sy4">;</span>
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file.<span class="me1">exceptions</span><span class="br0">(</span><a href="cpp-io-ios_base-iostate.html"><span class="kw1699">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">failbit</span></span></a><span class="br0">)</span><span class="sy4">;</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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std<span class="sy4">::</span><span class="me2">throw_with_nested</span><span class="br0">(</span> <a href="cpp-error-runtime_error.html"><span class="kw770">std::<span class="me2">runtime_error</span></span></a><span class="br0">(</span><span class="st0">"Couldn't open "</span> <span class="sy2">+</span> s<span class="br0">)</span> <span class="br0">)</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="co1">// 示例函数，捕捉异常并将其包装于 nested_exception</span>
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<span class="kw4">void</span> run<span class="br0">(</span><span class="br0">)</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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open_file<span class="br0">(</span><span class="st0">"nonexistent.file"</span><span class="br0">)</span><span class="sy4">;</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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std<span class="sy4">::</span><span class="me2">throw_with_nested</span><span class="br0">(</span> <a href="cpp-error-runtime_error.html"><span class="kw770">std::<span class="me2">runtime_error</span></span></a><span class="br0">(</span><span class="st0">"run() failed"</span><span class="br0">)</span> <span class="br0">)</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="co1">// 运行上述实例函数并打印捕捉的异常</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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<span class="kw1">try</span> <span class="br0">{</span>
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run<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</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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print_exception<span class="br0">(</span>e<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</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">exception: run() failed
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exception: Couldn't open nonexistent.file
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exception: basic_ios::clear</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-error-nested_exception.html"><span class="t-lines"><span>nested_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>用于捕获并存储当前异常的混入类型<br />
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<span class="t-mark">(类)</span></td>
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</tr>
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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-rethrow_if_nested.html"><span class="t-lines"><span>rethrow_if_nested</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>抛出 <span class="t-lc"><a href="cpp-error-nested_exception.html">std::nested_exception</a></span> 中的异常<br />
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<span class="t-mark">(函数模板)</span></td>
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