详解linux下避免僵尸进程的几种方法
<p>linux下我们可以调用fork函数创建子进程，创建的子进程将会得到父进程的数据空间、堆、栈......副本(采用写时复制机制)，子进程将会继承父进程的信号掩码、信号处理方式、当前工作目录、会话id、组id......。当子进程退出时父进程应当及时获取子进程退出状态，否则，如果父进程是一直在运行，那么子进程的退出状态将一直保存在内存中，直到父进程退出才释放。</p>
<p>
我们可以使用如下几种方法避免僵尸进程的产生:</p>
<p>
1.在fork后调用wait/waitpid函数取得子进程退出状态。</p>
<p>
2.调用fork两次（第一次调用产生一个子进程，第二次调用fork是在第一个子进程中调用，同时将父进程退出（第一个子进程退出），此时的第二个子进程的父进程id为init进程id（注意：新版本Ubuntu并不是init的进程id））。</p>
<p>
3.在程序中显示忽略SIGCHLD信号（子进程退出时会产生一个SIGCHLD信号，我们显示忽略此信号即可）。</p>
<p>
4.捕获SIGCHLD信号并在捕获程序中调用wait/waitpid函数。</p>
<p>
方法一：</p>
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<code class="cpp preprocessor">#include "../common/common.h"</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">)</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pid_t pid;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">((pid = fork()) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_FAILURE;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code><code class="cpp keyword bold">else</code> <code class="cpp keyword bold">if</code> <code class="cpp plain">(0 == pid) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"[%ld] child process is running...\n"</code><code class="cpp plain">, (</code><code class="cpp color1 bold">long</code><code class="cpp plain">)getpid());</code>
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<code class="cpp spaces"> </code><code class="cpp plain">_exit(0);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp comments">//sleep(15);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(waitpid(pid, NULL, 0) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"waitpid error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_FAILURE;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code> <code class="cpp plain">(; ;) {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pause();</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_SUCCESS;</code>
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<code class="cpp plain">}</code>
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<p>
方法二:</p>
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<code class="cpp preprocessor">#include <sys/wait.h></code>
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<code class="cpp preprocessor">#include "../common/common.h"</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pid_t pid;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">((pid = fork()) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_FAILURE;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code><code class="cpp keyword bold">else</code> <code class="cpp keyword bold">if</code> <code class="cpp plain">(0 == pid) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"first child is running..\n"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp comments">/**在第一个子进程中再次fork***/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">((pid = fork()) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_FAILURE;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code><code class="cpp keyword bold">else</code> <code class="cpp keyword bold">if</code> <code class="cpp plain">(pid > 0) {</code><code class="cpp comments">/**父进程退出**/</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"[%ld] first child is exit...\n"</code><code class="cpp plain">, (</code><code class="cpp color1 bold">long</code><code class="cpp plain">)getpid());</code>
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<code class="cpp spaces"> </code><code class="cpp plain">_exit(0);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp plain">sleep(2);</code><code class="cpp comments">/**确保父进程先运行**/</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"second process pid: %ld, second process's parent pid: %ld\n"</code><code class="cpp plain">, (</code><code class="cpp color1 bold">long</code><code class="cpp plain">)getpid(), (</code><code class="cpp color1 bold">long</code><code class="cpp plain">)getppid()); </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//sleep(15);</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"[%ld] is exit..\n"</code><code class="cpp plain">, (</code><code class="cpp color1 bold">long</code><code class="cpp plain">)getpid());</code>
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<code class="cpp spaces"> </code><code class="cpp plain">_exit(0);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp comments">/***获得第一个子进程的退出状态***/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(waitpid(pid, NULL, 0) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"waitpid error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_FAILURE;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code><code class="cpp plain">(;;)</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pause();</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_SUCCESS;</code>
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<code class="cpp plain">}</code>
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<p>
方法三：</p>
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<code class="cpp preprocessor">#include <signal.h></code>
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<code class="cpp preprocessor">#include "../common/common.h"</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">)</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp comments">/***显示忽略SIGCHLD信号****/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(</code><code class="cpp functions bold">signal</code><code class="cpp plain">(SIGCHLD, SIG_IGN) == SIG_ERR) {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pid_t pid;</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i;</code>
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<code class="cpp spaces"> </code><code class="cpp comments">/**产生10个子进程***/</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code> <code class="cpp plain">(i=0; i<10; ++i) {</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">((pid = fork()) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code> <code class="cpp plain">(; ;)</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pause();</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_SUCCESS;</code>
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<p>
方法四：</p>
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<code class="cpp preprocessor">#include <signal.h></code>
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<code class="cpp preprocessor">#include <sys/wait.h></code>
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<code class="cpp preprocessor">#include "../common/common.h"</code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">sig_chld(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">signo);</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">)</code>
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<div class="line number6 index5 alt1">
<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp comments">/**捕获此信号, 此刻系统会立刻检测是否有次信号产生**/</code>
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<div class="line number8 index7 alt1">
<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(</code><code class="cpp functions bold">signal</code><code class="cpp plain">(SIGCHLD, sig_chld) == SIG_ERR) {</code>
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<div class="line number9 index8 alt2">
<code class="cpp spaces"> </code><code class="cpp plain">handler_err(</code><code class="cpp string">"signal error to SIGCHLD"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pid_t pid;</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code> <code class="cpp plain">(i=0; i<10; i++) {</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">((pid = fork()) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">handler_err(</code><code class="cpp string">"fork error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code><code class="cpp keyword bold">else</code> <code class="cpp keyword bold">if</code> <code class="cpp plain">(0 == pid) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"child pid: %d\n"</code><code class="cpp plain">, getpid());</code>
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<code class="cpp spaces"> </code><code class="cpp plain">_exit(0);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp plain">sleep(1);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">continue</code><code class="cpp plain">;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code> <code class="cpp plain">(; ;) {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">pause();</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">EXIT_SUCCESS;</code>
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<code class="cpp plain">}</code>
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<code class="cpp comments">/**捕获到信号后会立刻执行此段代码***/</code>
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<code class="cpp keyword bold">void</code> <code class="cpp plain">sig_chld(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">signo)</code>
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<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"receive child signal\n"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(waitpid(-1, NULL, 0) < 0) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"waitpid error"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code> <code class="cpp plain">(</code><code class="cpp functions bold">signal</code><code class="cpp plain">(SIGCHLD, sig_chld) == SIG_ERR) {</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"signal error to SIGCHLD"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">}</code>
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<code class="cpp plain">}</code>
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<p>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。</p>
<p>
原文链接：http://blog.csdn.net/ComingFlying/article/details/76718809</p>
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