C: signal function (parameters?)

Question

I have the following c code:

void handler(int n) {
    printf("n value: %i\n");
}

int main() {
    signal(SIGTSTP, handler);   // ^Z at keyboard
    for(int n = 0; ; n++) {
    }   
}

I am curious what the n parameter is in the handler function. When you press ^Z it usually prints either: 8320, -1877932264 or -1073743664. What are these numbers?

---

Edit: Ops I wrote my printf wrong. I corrected it to be:

void handler(int n) {
    printf("n value: %i\n",n);
}

Now the value of n is always: 18. What is this 18?

Answer 1

You haven't passed any number to printf(). Should be:

void handler(int n) {
    printf("n value: %i \n", n);
}

The n will be the signum you are catching, in your case 20. See man 2 signal for a description. Also note that the manpage recommends using sigaction() instead of signal.