140 lines
11 KiB
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140 lines
11 KiB
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<title>setjmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_program_setjmp skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading">setjmp</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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="co2">#define setjmp(env) /* implementation-defined */</span></span></div>
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<p>保存当前执行环境到 <span class="t-lc"><a href="cpp-utility-program-jmp_buf.html">std::jmp_buf</a></span> 类型变量 <code>env</code> 。<span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 函数稍后可用此变量恢复当前执行环境。即在调用 <span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 函数时，执行在构造了传递给 <span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 的 <span class="t-lc"><a href="cpp-utility-program-jmp_buf.html">std::jmp_buf</a></span> 特定调用点继续。该情况下 <span class="t-lc"><strong class="selflink">setjmp</strong></span> 返回传递给 <span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 的值。</p>
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<p><code>setjmp</code> 的调用必须只出现在下列语境之一：</p>
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<ul>
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<li><a href="cpp-language-if.html">if</a> 、 <a href="cpp-language-switch.html">switch</a> 、 <a href="cpp-language-while.html">while</a> 、 <a href="cpp-language-do.html">do-while</a> 、 <a href="cpp-language-for.html">for</a> 语句的整个控制表达式</li>
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</ul>
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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="kw1">switch</span><span class="br0">(</span>setjmp<span class="br0">(</span>env<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span> ..</pre></div>
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</div>
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<ul>
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<li>比较或等于运算符的操作数之一，而另一操作数是整数常量表达式，产生的表达式是 <a href="cpp-language-if.html">if</a> 、 <a href="cpp-language-switch.html">switch</a> 、 <a href="cpp-language-while.html">while</a> 、 <a href="cpp-language-do.html">do-while</a> 、 <a href="cpp-language-for.html">for</a> 语句的整个控制表达式。</li>
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</ul>
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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="kw1">if</span><span class="br0">(</span>setjmp<span class="br0">(</span>env<span class="br0">)</span> <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span> ...</pre></div>
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</div>
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<ul>
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<li>一元 ! 运算符的操作数，产生的表达式是 <a href="cpp-language-if.html">if</a> 、 <a href="cpp-language-switch.html">switch</a> 、 <a href="cpp-language-while.html">while</a> 、 <a href="cpp-language-do.html">do-while</a> 、 <a href="cpp-language-for.html">for</a> 语句的整个控制表达式。</li>
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</ul>
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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="kw1">while</span><span class="br0">(</span><span class="sy3">!</span>setjmp<span class="br0">(</span>env<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span> ...</pre></div>
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</div>
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<ul>
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<li><a href="cpp-language-statements.html#.E8.A1.A8.E8.BE.BE.E5.BC.8F.E8.AF.AD.E5.8F.A5">表达式语句</a>（可以转型到 <code>void</code> ）的整个表达式。</li>
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</ul>
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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">setjmp<span class="br0">(</span>env<span class="br0">)</span><span class="sy4">;</span></pre></div>
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</div>
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<p>若 <code>setjmp</code> 出现于任何其他语境，则行为未定义。</p>
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<p>一旦返回到 <code>setjmp</code> 的作用域，所有可访问对象、浮点状态标志及其他抽象机组件拥有与在执行 <span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 时相同的值，除了含有 <code>setjmp</code> 调用的函数中的非 <a href="cpp-language-cv.html">volatile</a> 局部对象，在 <code>setjmp</code> 调用后更改它们，则其值不确定。</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>env</td>
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<td>-</td>
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<td>保存程序执行状态的变量。</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>若宏被原始代码调用且执行环境存储于 <code>env</code> 则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</p>
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<p>若刚进行了非局部跳转则返回非零值。返回值同传递给 <span class="t-lc"><a href="cpp-utility-program-longjmp.html">std::longjmp</a></span> 的值。</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>上述要求禁止在数据流中使用 <code>setjmp</code> 的返回值（例如以之初始化或赋值对象）。只能将返回值用于控制流或舍弃。</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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<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 <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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<a href="cpp-utility-program-longjmp.html"><span class="kw988">std::<span class="me2">longjmp</span></span></a><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">// 在 setjmp 作用域中被修改的局部变量必须是 volatile</span>
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<span class="kw1">if</span> <span class="br0">(</span>setjmp<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> <span class="co1">// 在一个 if 内不等于常量表达式</span>
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a<span class="br0">(</span><span class="sy2">++</span>count<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 这会导致 setjmp() 退出</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">a(1) called
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a(2) called
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a(3) called
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a(4) called
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a(5) called
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a(6) called
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a(7) called
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a(8) called</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-utility-program-longjmp.html"><span class="t-lines"><span>longjmp</span></span></a></div>
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</div>
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</td>
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<td>跳转到指定位置<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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</div>
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</body>
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