178 lines
11 KiB
HTML
178 lines
11 KiB
HTML
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<title>setjmp</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_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="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-program.html">program</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div>定义于头文件 <code><setjmp.h></code></div>
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<div><span class="mw-geshi c source-c"><span class="co2">#define setjmp(env) /* implementation-defined */</span></span></div>
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<p>将当前执行环境保存到 <span class="t-lc"><a href="c-program-jmp_buf.html">jmp_buf</a></span> 类型对象 <code>env</code> 。此对象可在之后被 <span class="t-lc"><a href="c-program-longjmp.html">longjmp</a></span> 函数用来恢复当前执行环境。即当调用 <span class="t-lc"><a href="c-program-longjmp.html">longjmp</a></span> 函数时，执行将从传递给 <span class="t-lc"><a href="c-program-longjmp.html">longjmp</a></span> 的 <span class="t-lc"><a href="c-program-jmp_buf.html">jmp_buf</a></span> 对象所构建的特定调用点继续。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="c-program-longjmp.html">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中：</p>
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<ul>
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<li>选择或迭代语句（ if 、 switch 、 for 、 while 、 do-while ）的完整控制表达式</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="c source-c">
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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>比较或相等运算符的一个运算数，另一运算数为整数常量表达式，产生的表达式为选择或迭代语句的完整控制表达式</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="c source-c">
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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">10</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 ! 运算符的运算数，其结果为选择或迭代语句的完整控制表达式</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="c source-c">
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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>表达式语句的完整表达式（可以将其转型到 <code>void</code> ）。</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="c source-c">
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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> 出现于其他语境中，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="c-program-longjmp.html">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>要保存程序执行状态的对象。</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>若原初代码调用该宏，则返回 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> ，并保存执行环境到 <code>env</code> 。</p>
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<p>若进行了非局部跳转则可返回非零值。返回值与传递给 <span class="t-lc"><a href="c-program-longjmp.html">longjmp</a></span> 者相同。</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <setjmp.h></span>
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<span class="co2">#include <stdnoreturn.h></span>
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<a href="c-program-jmp_buf.html"><span class="kw510">jmp_buf</span></a> jump_buffer<span class="sy4">;</span>
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noreturn <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="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"a(%d) called<span class="es1">\n</span>"</span>, count<span class="br0">)</span><span class="sy4">;</span>
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<a href="c-program-longjmp.html"><span class="kw509">longjmp</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">// 将从 setjmp 外 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="kw4">void</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">// setjmp 作用域内要修改的局部变量必须为 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="co1">// 在一个 if 内与常数比较</span>
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a<span class="br0">(</span>count<span class="sy2">++</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">a(0) called
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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.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.13.1.1 The setjmp macro (p: 262-263)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.13.1.1 The setjmp macro (p: 243-244)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.6.1 The setjmp macro</li>
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</ul>
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</dd>
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</dl>
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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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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="c-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>
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</div>
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<div class="visualClear"></div>
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</div>
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