setjmp(3c)                 DG/UX 4.30                  setjmp(3c)



     NAME
          setjmp, longjmp - non-local goto

     SYNOPSIS
          #include <setjmp.h>

          int setjmp (env)
          jmpbuf env;

          void longjmp (env, val)
          jmpbuf 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 (which must not itself have
          returned in the interim) had just returned the value val.
          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.

          In a future release, C language users will be able to
          identify syntactically those automatic variables on whose
          values they need to rely after the second return from
          setjmp.

     EXAMPLE
          #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);
             }



     Licensed material--property of copyright holder(s)         Page 1

     setjmp(3c)                 DG/UX 4.30                  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

     SEE ALSO
          signal(2).

     WARNING
          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.































     Licensed material--property of copyright holder(s)         Page 2