setjmp(3C)             UNIX System V(C Development Set)              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, 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>

      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()


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setjmp(3C)             UNIX System V(C Development Set)              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.





































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