setjmp(3C)           COMPATIBILITY FUNCTIONS           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 pro-
     gram.

     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.

EXAMPLE
     #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);
         }
         (void) printf("value of i on 1st return from setjmp: %d\n", i);
         i = 1;
         g();



          Last change: C Programming Language Utilities         1

setjmp(3C)           COMPATIBILITY FUNCTIONS           setjmp(3C)



         /* 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), 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.


































          Last change: C Programming Language Utilities         2