signal() and sigaction()

signal-vs-sigaction.c

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

void signal_handler_function(int signo);

typedef void (*sighandler_t)(int);

int main()
{
  //m=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
  // Old: Use of signal()

  // Set errno to zero before the call.
  errno = 0;
  sighandler_t old_sighandler = signal(SIGINT, signal_handler_function); // OR
  // signal(SIGINT, &signal_handler_function);

  if(old_sighandler == SIG_ERR)
  {
    fprintf(
      stderr,
      "signal() failed...\n"
      "signum is invalid\n"
    );

    exit(1);
  }


  //m=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
  // New: Use of sigaction()
  struct sigaction act;
  struct sigaction oldactions;

  memset(&act, 0, sizeof(act));
  act.sa_handler = signal_handler_function;
  sigfillset(&act.sa_mask);
  act.sa_flags = 0;

  // Set errno to zero before the call.
  errno = 0;
  int sigaction_return = sigaction(SIGINT, &act, &oldactions);

  if (sigaction_return == -1)
  {
    fprintf(stderr, "sigaction() failed\n");
    if (errno == EFAULT)
    {
      fprintf(stderr, "act or oldact not part of address space\n");
      exit(2);
    }
    else
    {
      fprintf(stderr, "Invalid signal specified.\n");
      exit(3);
    }
  }

  sigaction_return = sigaction(SIGINT, &oldactions, NULL);

  return 0;
}


void signal_handler_function(int signo)
{
  printf("Handled signal %d.\n", signo);
}