Why do programs usually use signal (sigchld, sig_dfl)

Why sigchld (sigchld, sig_dfl) is usually used in the program to execute the system function, the sigchld signal should be displayed: Signal (sigchld, sig_dfl), because in the system function, used fork (), waitpid. if the parent process ignores the sigchid signal and the waitpid does not get the sigchld signal of the child process, the returned value will be faulty. The returned value of system may also be faulty. The common practice is: Signal (sigchld, sig_dfl); System (command); signal (sigchld, sig_ign); Jesus love you! Reprinted from: http://blog.sina.com.cn/s/blog_633685790101ks9q.html

 

Why do programs usually use signal (sigchld, sig_dfl)