Question

I am a newbie in Linux programming.I copied the code below from a book:

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

void ouch (int sig)
{
    printf("OUCH! - I got signal %d\n", sig);
    (void) signal(SIGINT, SIG_DFL);
}

int main ()
{
    (void) signal(SIGINT, ouch);

    while(1)
    {
        printf("Hello World!\n");
        sleep(1);
    }

}

It was expected to print something when Ctrl+C was entered.But it do nothing but print Hello World!.

---

EDIT:
I am so sorry that I have binded the Ctrl+C as a short-cut key for copy.
Sorry for trouble caused.

Answer 1

My Suggestion is don’t use printf in siginal handler (ouch), it may be undefined behavior. Async-signal-safe functions: The list of safe functions that can be call in signal handler man page.

It is not safe to call all functions, such as printf, from within a signal handler.
A useful technique is to use a signal handler to set a flag and then check that flag
from the main program and print a message if required.

_{Reference: Beginning Linux Programming, 4th Edition,In this book exactly your code is explained, Chapter 11: Processes and Signals, page 484}

An additional helpful link:
Explanation: Use reentrant functions for safer signal handling