setjmp(3C)                       DG/UX 5.4.2                      setjmp(3C)


NAME
       setjmp, longjmp - non-local goto

SYNOPSIS
       #include <setjmp.h>

       int setjmp (jmpbuf env);

       void longjmp (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, jmpbuf, 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.

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

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



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

setjmp(3C)                       DG/UX 5.4.2                      setjmp(3C)


           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), sigsetjmp(3C).

NOTES
       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)                         2