Write a program that shows that when the disposition of a pending signal is changed to be SIG_IGN , the program never sees (catches) the signal.

change_pending_signals_disposition.c

// Write a program that shows that when the disposition of a pending signal is
// changed to be SIG_IGN , the program never sees (catches) the signal.

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

void printSigset(FILE *of, const char *prefix, const sigset_t *sigset)
{
    int sig, cnt;

    cnt = 0;
    for (sig = 1; sig < NSIG; sig++) {
        if (sigismember(sigset, sig)) {
            cnt++;
            fprintf(of, "%s--%d\n", prefix, sig);
        }
    }

    if (cnt == 0)
        fprintf(of, "%s<empty signal set>\n", prefix);
}

static void handler(int sig) {
    printf("Caught %d\n", sig);
}

static void handler2(int sig) {
    printf("2Caught %d\n", sig);
}

int main(int argc, char const *argv[]) {
    struct sigaction act;
    act.sa_handler = handler;
    sigaction(SIGINT, &act, NULL);
    sigset_t blockingMask, emptyMask;
    sigemptyset(&blockingMask);
    sigaddset(&blockingMask, SIGINT);
    sigprocmask(SIG_SETMASK, &blockingMask, NULL);

    printSigset(stdout, "joseph", &blockingMask);

    act.sa_handler = SIG_IGN;
    sigaction(SIGINT, &act, NULL);
    sigemptyset(&emptyMask);        /* Unblock all signals */
    sigprocmask(SIG_SETMASK, &emptyMask, NULL);
    while (1) {
        pause();
    }
    return 0;
}