sigismember example

#include <signal.h>
#include <errno.h>

/* 

 * <signal.h> usually defines NSIG to include signal number 0 

 */

#define SIGBAD(signo) ((signo) <= 0 || (signo) >= NSIG)

int sigismember(const sigset_t *set, int signo) {
    if (SIGBAD(signo)) {
        errno = EINVAL; return(-1);
    }
    return((*set & (1 << (signo - 1))) != 0);
}

See Also

1. sigdelset
2. sigaddset