I am playing with the signal.h and unistd.h libraries, and I am having some issues. In the code below, when I send the SIGINT signal to my running program by calling CTRL-C, the signal is caught. However, when pressing CTRL-C again, the program terminates. As I understand it, the print statement "Received signal 2" should be printed every time I press CTRL-C.
Is my understanding of this signal incorrect, or is there a bug in my code?
Thanks for your input!
#include "handle_signals.h"
void sig_handler(int signum)
{
printf("\nReceived signal %d\n", signum);
}
int main()
{
signal(SIGINT, sig_handler);
while(1)
{
sleep(1);
}
return 0;
}
Terminal output:
xxx@ubuntu:~/Dropbox/xxx/handle_signals$ ./handle_signals
^C
Received signal 2
^C
xxx@ubuntu:~/Dropbox/xxx/handle_signals$
Edit: Here is the header I've included
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
void sig_handler(int signum);
Thanks for your responses. Reading through them now!
Don't use signal, use sigaction:
The behavior of signal() varies across UNIX versions, and has also varied historically across different versions of Linux. Avoid its use: use sigaction(2) instead.
http://man7.org/linux/man-pages/man2/signal.2.html
In the original UNIX systems, when a handler that was established using signal() was invoked by the delivery of a signal, the disposition of the signal would be reset to SIG_DFL, and the system did not block delivery of further instances of the signal.
Linux implements the same semantics: the handler is reset when the signal is delivered.
The behaviour of signal upon receiving the first signal varies on different implementation. Typically, it requires reinstalling the handler after receiving the signal as handler is reset to its default action:
void sig_handler(int signum)
{
signal(SIGINT, sig_handler);
printf("\nReceived signal %d\n", signum);
}
which is one of the reasons you shouldn't use signal anymore and use sigaction. You can see a bare bone example of using sigaction here.