指定bit位置1和清0

#define SIGHUP         1
#define SIGINT         2
#define SIGQUIT        3
#define SIGILL         4
#define SIGTRAP        5
#define SIGABRT        6
#define SIGBUS         7
#define SIGFPE         8
#define SIGKILL        9
#define SIGUSR1        10
#define SIGSEGV        11
#define SIGUSR2        12
#define SIGPIPE        13
#define SIGALRM        14
#define SIGTERM        15
#define SIGSTKFLT      16
#define SIGCHLD        17
#define SIGCONT        18
#define SIGSTOP        19
#define SIGTSTP        20
#define SIGTTIN        21
#define SIGTTOU        22
#define SIGURG         23
#define SIGXCPU        24
#define SIGXFSZ        25
#define SIGVTALRM      26
#define SIGPROF        27
#define SIGWINCH       28
#define SIGIO          29
#define SIGPWR         30
#define SIGSYS         31
#define SIGRTMIN       32

void main(void)
{
     unsigned long signal;
     signal &= ~( (1<<(SIGSTOP-1)) | (1<<(SIGTSTP-1)) | (1<<(SIGTTIN-1)) | (1<<(SIGTTOU-1)) ); //指定位清0，其他位保持
      signal |= 1 << (SIGSTOP-1); //指定位置1，其他位保持
}