Run something once the program has been terminated using CTRL+C

Question

Is there any way to run a function before a program terminates? eg. the user presses ctrl+c and you want to print something to them. Thanks!

Sorry, I should be more specific - this is for Linux – user92489827 Jun 07 '15 at 05:33 — user92489827, Jun 07 '15 at 05:33

Levi · Answer 1 · 2015-06-07T05:42:37.943

3

For *nix systems, you can use the signal() function.

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

volatile sig_atomic_t sig_flag = 0;

void sig_handler(int sig)
{
    // A signal has been received. Set `sig_flag` to the value of the signal
    sig_flag = sig;
}

int main()
{
    // Call sig_handler on SIGINT (Ctrl-C)
    signal(SIGINT, sig_handler);

    while (sig_flag != SIGINT);
    printf("Bye\n");

    return 0;
}

EDIT: As per Basile's comment, I should mention that only a select few functions are safe to use under a signal handler, as the handler is called asynchronously. The list of safe functions are available under signal(7)

edited Jun 07 '15 at 05:42

answered Jun 07 '15 at 05:23

Levi

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Yes, but you should mention async signal safe, and perhaps refer explicitly to [signal(7)](http://man7.org/linux/man-pages/man7/signal.7.html) – Basile Starynkevitch Jun 07 '15 at 05:39
How would I use this example if I wanted to pass parameters into that function? (without the use of global variables, if pssible) – user92489827 Jun 07 '15 at 05:39
1

@user92489827: you cannot pass parameters to signals, you need to use global variables. And as I am trying to explain, signal handlers should be *very* simple – Basile Starynkevitch Jun 07 '15 at 05:40
BTW, you can't run something *once* a program terminates, but *before* it does (and *after* `SIGINT` has been recieved) – Basile Starynkevitch Jun 07 '15 at 05:41
1

On Linux specifically, you could also use [signalfd(2)](http://man7.org/linux/man-pages/man2/signalfd.2.html) and poll that descriptor in your event loop – Basile Starynkevitch Jun 07 '15 at 05:42
@BasileStarynkevitch I'm trying to keep my answer somewhat generic (see the *nix in the first line of the answer) – Levi Jun 07 '15 at 05:44
BTW, `signal` is nearly deprecated. The correct way is to use `sigaction` – Basile Starynkevitch Jun 07 '15 at 05:44

Run something once the program has been terminated using CTRL+C

1 Answers1