Examining the return valu of signal function

sig.c

/* 
 * sig.c - examining the return value of the signal function
 *
 * The signal function returns the pointer to the previous
 * handler for the signal.
 */

#include <stdio.h>		/* for printf */
#include <signal.h>		/* for signal */
#include <stdlib.h> 		/* for exit */
#include <unistd.h>

typedef void (*sig_t) (int); 	/* A void function*/

static sig_t prev;

/* some_fun - a simple signal handler */
void some_fun()
{
  printf("\nBye!\n");
  exit(0);
}

/* set_handler - set the SIGINT handler and store the previous
 *               value
 */
void set_handler( sig_t handler )
{
  prev = signal(SIGINT, handler);
  printf("SIGINT was previously handled by %p ", prev);
  printf("and should now be handled by %p\n", handler);
  printf("3...");
  fflush(stdout);
  sleep(1);

  printf("2...");
  fflush(stdout);
  sleep(1);
  
  printf("1...");
  fflush(stdout);
  sleep(1);
  
  printf("\n");
}

int main(){

  printf("some_fun is at address: %p\n", some_fun);
  printf("SIG_DFL is at addrss: %p\n", SIG_DFL);
  
  set_handler(some_fun);
  set_handler(prev);

}