问题描述
这是我的代码示例
signal(SIGCHLD, SIG_IGN);
ret = system("ls -al");
if(ret < 0)
{
perror("system failed");
printf("return value is %d\n", ret);
}
ls -al 命令可以毫无问题地执行。
The ls -al command can be executed without any problem.
但是 system（）的返回值始终为-1。在这种情况下，我无法获得命令的实际返回值。
But the return value of system() is always -1. In this case, I can't get the real return value of the command.
某些参考文献指出忽略SIGCHLD会影响 waitpid（）在 system（）中，这就是为什么 system 总是返回-1的原因。
Some reference says that ignore SIGCHLD would affect waitpid() in system(), that's why system always returns -1.
但令我更加困扰的是：默认情况下，SIGCHLD是否不被忽略？那么，为什么显式地忽略SIGCHLD会导致这种情况呢？
But what puzzles me more is that: isn't SIGCHLD ignored by default? So why ignoring SIGCHLD explicitly would result in such case?
有人可以向我解释吗？
@cnicutar现在我了解忽略SIGCHLD的影响。
Thanks to @cnicutar now I understand the effects of ignoring SIGCHLD.
但是现在我想知道是否有任何方法可以在忽略SIGCHLD的情况下获取子进程的返回值？还是由于POSIX规范和OS实现而这不可能吗？
But now I'm wondering is there any methods to get the return value of child process while SIGCHLD is ignored? Or is this just impossible due to the POSIX specification and OS realizaiton?
推荐答案
否，默认情况下不会被忽略。默认情况下，根本没有处理程序并且不执行任何操作。
No, by default it is not ignored. By default there is simply no handler and no action is taken.
忽略 SIGCHLD 有一个有趣的副作用：孩子不会变成僵尸。
Ignoring SIGCHLD has an interesting side-effect: children don't become zombies.
也就是说，您无需再等待孩子了，因为他们会被自动收集。但是 system（3）想要一个孩子！因此， waitpid 返回错误，并且 system（3）起作用。
That is, you don't need to wait any longer for children since they get collected automatically. But system(3) expected a child! So waitpid returns an error and system(3) behaves.
这篇关于忽略SIGCHLD的system（）函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！