SIG函数

       #include <signal.h>


       int sigemptyset(sigset_t *set);


       int sigfillset(sigset_t *set);


       int sigaddset(sigset_t *set, int signum);


       int sigdelset(sigset_t *set, int signum);


       int sigismember(const sigset_t *set, int signum);


DESCRIPTION
       The sigsetops(3) functions allow the manipulation of POSIX signal sets.


       sigemptyset() initializes the signal set given by set to empty, with all signals excluded from the set.

初始化信号set，置set为空
       sigfillset() initializes set to full, including all signals.
       初始化set满，包括所有信号

       sigaddset() and sigdelset() add and delete respectively signal signum from set.
增加一个信号 删除一个信号从set中

       sigismember() tests whether signum is a member of set.

检测某个信号是否在set中