setjmp(3C)                                                setjmp(3C)


       NAME
             setjmp, longjmp - non-local goto

       SYNOPSIS
             #include <setjmp.h>
             int setjmp (jmp_buf env);
             void longjmp (jmp_buf env, int val);

       DESCRIPTION
             These functions are useful for dealing with errors and
             interrupts encountered in a low-level subroutine of a program.

             setjmp saves its stack environment in env (whose type,
             jmp_buf, is defined in the <setjmp.h> header file) for later
             use by longjmp.  It returns the value 0.

             longjmp restores the environment saved by the last call of
             setjmp with the corresponding env argument.  After longjmp is
             completed, program execution continues as if the corresponding
             call of setjmp had just returned the value val.  (The caller
             of setjmp must not have returned in the interim.)  longjmp
             cannot cause setjmp to return the value 0.  If longjmp is
             invoked with a second argument of 0, setjmp will return 1.  At
             the time of the second return from setjmp, all external and
             static variables have values as of the time longjmp is called
             (see example).  The values of register and automatic variables
             are undefined.

             Register or automatic variables whose value must be relied
             upon must be declared as volatile.

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

                   jmp_buf env;
                   int i = 0;
                   main ()
                   {
                       void exit();

                       if(setjmp(env) != 0) {
                          (void) printf("value of i on 2nd return from setjmp: %d\n", i);
                          exit(0);
                       }


                           Copyright 1994 Novell, Inc.               Page 1

      setjmp(3C)                                                setjmp(3C)


                      (void) printf("value of i on 1st return from setjmp: %d\n", i);
                      i = 1;
                      g();
                      /* NOTREACHED */
                  }
                  g()
                  {
                      longjmp(env, 1);
                      /* NOTREACHED */
                  }

            If the a.out resulting from this C language code is run, the
            output will be:

                  value of i on 1st return from setjmp:0
                  value of i on 2nd return from setjmp:1

      REFERENCES
            signal(2), sigsetjmp(3C)

      NOTICES
            If longjmp is called even though env was never primed by a
            call to setjmp, or when the last such call was in a function
            that has since returned, absolute chaos is guaranteed.
























                          Copyright 1994 Novell, Inc.               Page 2