setjmp(3)                           CLIX                           setjmp(3)



  NAME

    setjmp, longjmp - Provides a nonlocal goto

  LIBRARY

    Standard C Library (libc.a)

  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 program.

    The setjmp() function 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.

    The longjmp() function 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.  The longjmp() function 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().

  EXAMPLES

    To use setjmp():

    #include <setjmp.h>

    jmp_buf env;
    int i = 0;



  2/94 - Intergraph Corporation                                              1

  setjmp(3)                           CLIX                           setjmp(3)



    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


  CAUTIONS

    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.

  RETURN VALUES

    The setjmp() function returns 0.  The longjmp() function does not return a
    value.

  RELATED INFORMATION

    Functions:  signal(2)













  2                                              Intergraph Corporation - 2/94