How to use a signal handler in Unix?

Question

I am learning about signals. In the following code, how can I keep printing the prompt inside the while loop after the CTRL-C signal has been entered. Also how to terminate the process with the CTRL-D signal.

int main(int argc, char *argv[]){  

    struct sigaction sh;
    sh.sa_handler = sigint_handler;
    sigemptyset(&sh.sa_mask);
    sh.sa_flags = 0;
    sigaction(SIGINT, &sh, NULL);

    while(1)
    {
        printf("Some prompt: ");
    }
    return 0;
}

You need to show more code (e.g. the `sigint_handler()` function), and you also need to use less code (use `int main(void)` since you don't pay any attention to `argc` or `argv`). Don't forget that by default, standard output will be line-buffered. That means you won't see the prompt until the buffer is filled. — Jonathan Leffler, Dec 06 '19 at 03:36
And also do a search. There a quite a few existing questions on how to ignore and handle signals. There is even a question that is almost identical to this one: https://stackoverflow.com/questions/2485028/signal-handling-in-c. — kaylum, Dec 06 '19 at 03:39
Note what is discussed in [How to avoid using `printf()` in a signal handler](https://stackoverflow.com/questions/16891019/) — and maybe [What is the difference between `signal()` and `sigaction()`?](https://stackoverflow.com/questions/231912/) — Jonathan Leffler, Dec 06 '19 at 03:42
Does this answer your question? [Signal Handling in C](https://stackoverflow.com/questions/2485028/signal-handling-in-c) — kaylum, Dec 06 '19 at 03:43

Basile Starynkevitch · Answer 1 · 2019-12-06T03:55:52.330

How to use signal handler in unix?

Read signal(7) and most importantly signal-safety(7). Use fflush(3) appropriately, since stdio(3) is buffered.

Also how to terminate the process with the CTRL-D signal.

But Ctrl D is not a signal. See stty(1). It triggers the end of file condition on stdin when that is a terminal. See isatty(3) and pty(7). To detect that end of file condition, see read(2) and feof(3).

How to use a signal handler in Unix?

1 Answers1