setjmp()                Save Program State

 #include   <setjmp.h>

 int        setjmp(env);
 jmp_buf    env;                         Variable environment is stored in

    setjmp() and its companion routine longjmp() provide a method of
    executing a non-local goto. They are typically used to pass control
    to error-handling code in a previously called routine without using
    the normal calling conventions.

    setjmp() saves the current stack environment in 'env'. A subsequent
    call to longjmp() restores the stack environment and returns control
    to the point just after the setjmp() call.  All variables (except
    register variables) accessible to the calling routine contain the
    values they had when longjmp() was called.

       Returns:     setjmp() returns the value 0 after it saves the stack
                    environment. If setjmp() returns because of a
                    subsequent longjmp() call, it returns the 'value'
                    argument from longjmp() (The 'value' argument cannot
                    be 0). There is no error return.

         Notes:     The values of register variables in the routine
                    calling setjmp() may be restored incorrectly after
                    the longjmp().

   -------------------------------- Example ---------------------------------

    The following statements use setjmp() and longjmp() to save and
    restore a stack environment.

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

           int val;
           jmp_buf jump;

           main()
           {
               val = setjmp(jump);
               if (val != 0)
               {
                  printf("longjmp called. control returned to setjmp.
                          val: %d\n", val);
                  exit(val);
               }
               printf("setjmp first called, val is %d\n",val);
               s();
            }

           s()
           {
               printf("subroutine called\n");
               longjmp(jump,1);
           }