Combining setjmp()/longjmp() and Signal Handling

Combining setjmp()/longjmp() and signal handling, we will be able to catch a signal and then jump to some other places for further or special processing rather than going back to the interrupted statement.

Here is a simple example. Click here to download a copy of this program.

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

jmp_buf  JumpBuffer;

void     INThandler(int);

void  main(void)
{
     signal(SIGINT, INThandler);

     while (1) {
          if (setjmp(JumpBuffer) == 0) {
             printf("Hit Ctrl-C at anytime ... \n");
                  pause();
          }
     }
}

void  INThandler(int  sig)
{
     char  c;

     signal(sig, SIG_IGN);
     printf("OUCH, did you hit Ctrl-C?\n"
            "Do you really want to quit? [y/n] ");
     c = getchar();
     if (c == 'y' || c == 'Y')
          exit(0);
     else {
          signal(SIGINT, INThandler);
          longjmp(JumpBuffer, 1);
     }
}

• Function INThandler() handles signal SIGINT. Its activity is almost identical to a previous example, except that this one uses longjmp() to go back.
• The main program first installs INThandler() as the signal handler for SIGINT. Then, the main program enters an infinite loop. In each iteration, the main program creates a jump buffer for longjmp() to jump back. Then, displays a message asking the user to press the Ctrl-C and pauses itself.
• If the user presses Ctrl-C, this generates signal SIGINT and INThandler() will be called (by the system) to process this signal. As mentioned earlier, rather than returning to the interrupted statement, this version always sends the control back to the setjmp() in the main program.
• The following figure illustrates this concept: