Here is an example of registering a user defined signal handler for the SIGINT signal. Note the signal is sent to a process by typing ctrl-c in the console/window where the process is running.

    1   /*------------------------------------------------------------------------
    2   | 
    3   |       File: signal03.c
    4   | 
    5   |       Description: This program repeatedly increments a counter. When
    6   |       overflow occurs, it increments an separate overflow counter.
    7   |       It has an infinite loop. Typing ctrl-c at the keyboard sends
    8   |       this process a SIGINT signal. A signal handler, sigint_handler
    9   |       catches the signal increments a signal counter and prints the
   10   |       current counts. The signal handler terminates the program when
   11   |       a maximum number of allowed SIGINT signals have been received.
   12   |       The user defined sigint_handler function executes instead of
   13   |       the default handler since sigint_handler is registered as
   14   |       the handler (the signal function does this).
   15   |       
   16   | 
   17   |       Created: 12 Jan 15
   18   |       Author: glancast
   19   | 
   20   +-----------------------------------------------------------------------*/
   21   #include <stdio.h>
   22   #include <stdlib.h>
   23   #include <signal.h>
   24   
   25   const int MAXSIGNALS = 5;
   26   
   27        void sigint_handler(int sig);
   28   
   29   /**
   30    * Counters are global so that
   31    * the signal handler can access them.
   32    */
   33   int cnt = 0;
   34   int overflow = 0;
   35   int signals = 0;
   36   
   37   
   38   int main(int argc, char *argv[])
   39   {
   40     printf("This program increments a counter. Type ctrl-c to send a SIGINT signal.\n");
   41     printf("%d maximum number of SIGINT signals allowed.\n", MAXSIGNALS);
   42   
   43          signal(SIGINT, sigint_handler);
   44     
   45     while(1) {
   46       if (cnt + 1 < cnt) {
   47         cnt = 0;
   48         overflow++;
   49       } else {
   50         cnt++;
   51       }
   52     }
   53   
   54     return 0;
   55   }
   56   
   57   
   58     void sigint_handler(int sig)
   59  {
   60    signals++;
   61    printf("\nsigint %d: overflow = %d, count = %d\n", signals, overflow, cnt);
   62    if (signals == MAXSIGNALS) {
   63      printf("\nMaximum number of SIGINT signals allowed is %d. Exiting\n", MAXSIGNALS);
   64      printf("Edit MAXSIGNALS if you want more!\n\n");
   65      exit(0);
   66    }
   67  
   68  }