SETJMP(3C)                           SysV                           SETJMP(3C)



NAME
     setjmp, longjmp - non-local goto

SYNOPSIS
     #include <setjmp.h>

     int setjmp (env)
     jmp_buf env;

     void longjmp (env, val)
     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 (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 accessible data have values as of the time
     longjmp is called.  However, global variables will have the expected
     values, that is those as of the time of the longjmp (see example).

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);
          }
          (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) siglongjmp(3C), sigsetjmp(3C).

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 which has since
     returned, absolute chaos is guaranteed.

BUGS
     The values of the registers on the second return from setjmp are the
     register values at the time of the first call to setjmp, not those at the
     time of the longjmp.  This means that variables in a given function may
     behave differently in the presence of setjmp, depending on whether they
     are register or stack variables.