sigaction is catching signal only once

Question

Consider the following code:

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

    void catch ()
    {
        printf("hi\n");
    }
    int main()
    {
        struct sigaction act;
        act.sa_handler = catch;
        sigaction(SIGINT, &act, NULL);
        for(;;);
        return 0;
    }

When this program is run. The first time I press CTRL-C it prints "hi".
But the second time the program exits. what could be the reason for this?
What I wanted was that the program catch the signal each time it is raised.

Answer 1

If you don't use any SA_FLAG to explicitly define the behavior of "what to do after first catch of signal", it should be work.

Clear the contents of the sigaction, then initialize it.

memset(&act,0,sizeof(act)); // clear contents first
act.sa_handler = catch;
sigaction(SIGINT, &act, NULL);

See, sigaction(2).

In addition, do not use printf inside your signal handlers as Daniel pointed out. See signal-safety(7)

If you want to print something, or simply do something in your signal handler, you must use signal-safe functions. In your case, instead of using printf, you can use write() system call. See write(2).

By,

write(1,"hi\n",3); // 1 means standard out.