127 lines
8.8 KiB
HTML
127 lines
8.8 KiB
HTML
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<title>std::longjmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_program_longjmp 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>longjmp</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-program.html">program</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-csetjmp.html"><csetjmp></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"> <span class="kw4">void</span> longjmp<span class="br0">(</span> <a href="cpp-utility-program-jmp_buf.html"><span class="kw989">std::<span class="me2">jmp_buf</span></span></a> env, <span class="kw4">int</span> status <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx17">(C++17 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="br0">[</span><span class="br0">[</span>noreturn<span class="br0">]</span><span class="br0">]</span> <span class="kw4">void</span> longjmp<span class="br0">(</span> <a href="cpp-utility-program-jmp_buf.html"><span class="kw989">std::<span class="me2">jmp_buf</span></span></a> env, <span class="kw4">int</span> status <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>加载先前的 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 调用所保存的执行环境 <code>env</code> 。此函数不返回。控制被转移到设置了 <code>env</code> 的宏 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 的调用点。该 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 随后返回作为 <code>status</code> 传递的值。</p>
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<p>若调用了 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 的函数已退出，则行为未定义（换言之，仅允许在调用栈向上长跳）</p>
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<p>不调用任何自动对象的析构函数。若以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">throw</span></span></span> 替换 <code>std::longjmp</code> 且以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">catch</span></span></span> 替换 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 会执行任何自动对象的非平凡析构函数，则这种 <code>std::longjmp</code> 的行为未定义。</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>env</td>
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<td>-</td>
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<td>指代 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-program-setjmp.html"><span class="kw988">setjmp</span></a></span></span> 所保存的函数执行状态的变量</td>
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<td>status</td>
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<td>-</td>
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<td>从 <span class="t-lc"><a href="cpp-utility-program-setjmp.html">setjmp</a></span> 返回的值。若它等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，则以用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span> 代替</td>
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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=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p><code>longjmp</code> 是 C 中处理函数无法有意义返回处的错误条件的机制。 C++ 通常为此目的使用<a href="cpp-language-exceptions.html">异常处理</a>。</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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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <csetjmp></span>
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<a href="cpp-utility-program-jmp_buf.html"><span class="kw989">std::<span class="me2">jmp_buf</span></span></a> jump_buffer<span class="sy4">;</span>
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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> a<span class="br0">(</span><span class="kw4">int</span> count<span class="br0">)</span>
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<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">"a("</span> <span class="sy1"><<</span> count <span class="sy1"><<</span> <span class="st0">") called<span class="es1">\n</span>"</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">longjmp</span><span class="br0">(</span>jump_buffer, count<span class="sy2">+</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// setjump() 将返回 count+1</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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<span class="kw4">volatile</span> <span class="kw4">int</span> count <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// 必须为 setjmp 设定局部变量为 volatile</span>
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<span class="kw1">if</span> <span class="br0">(</span><a href="cpp-utility-program-setjmp.html"><span class="kw988">setjmp</span></a><span class="br0">(</span>jump_buffer<span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">9</span><span class="br0">)</span> <span class="br0">{</span>
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a<span class="br0">(</span>count<span class="sy2">++</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// This will cause setjmp() to exit</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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<p>输出：</p>
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<pre class="de1">a(0) called
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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-utility-program-setjmp.html"><span class="t-lines"><span>setjmp</span></span></a></div>
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<td>保存语境<br />
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<span class="t-mark">(宏函数)</span></td>
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