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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 would typically be 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() will restore the stack environment and return
    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 the
                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 incorrectly restored 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);
         }