Re: Question regarding passing variables to ILE-RPG from C

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

On 13/01/2006, at 11:33 AM, Barbara Morris wrote:

> Simon Coulter wrote:
> > Problem 2 is that C expects an int (4 bytes) but the prototype is
> > passing a 2-byte integer. RPG will widen the value because that's what
> > C expects but you shouldn't rely on this behaviour.
>
> Actually, RPG doesn't widen the value.  Sometimes the parameter can get
> passed in a register, and that makes it appear as though RPG widened 
> the
> value, but if the system doesn't have a register available, the
> parameter gets passed "on the stack" (I don't know the mechanism).  
> When
> that happens, the called function doesn't get the value that the caller
> passed.

I'd always understood RPG didn't widen and I fully expected the 
original example to fail due to the RPG prototype specifying a 2-byte 
integer but I tried it in debug to confirm and the C function received 
a 4-byte integer if I passed either a literal, a 5I0, or a 10I0 so I 
presumed RPG was widening it.

Hmm, what would happen if the C function expected a short and the value 
was passed in a register? I presume I don't have to worry about this 
and it will be "taken care of" by the run time.

Regards,
Simon Coulter.
--------------------------------------------------------------------
   FlyByNight Software         AS/400 Technical Specialists

   http://www.flybynight.com.au/
   Phone: +61 3 9419 0175   Mobile: +61 0411 091 400        /"\
   Fax:   +61 3 9419 0175                                   \ /
                                                             X
                 ASCII Ribbon campaign against HTML E-Mail  / \
--------------------------------------------------------------------