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

Simon Coulter wrote:
> 
> 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.
> 

Yes, that's correct.  This is all handled a few levels below the RPG
compiler, so I don't know exactly how "it" "knows" about the register,
but I think it works for the same reason the following works:

    D longInt       s       20i 0
    D int           s       10i 0
    D shortInt      s        5i 0

"Pass" the shortInt value to int via longInt
       longInt = shortInt
       int = longInt
"Pass" the int value to shortInt via longInt
       longInt = int
       shortInt = int

The transfer mechanism (the register or my "longInt") is at least as
long as the other operands in the transaction, and in both the register
case and my example below, the system knows everything it needs to know
to get it right, assuming you have told the truth to the compilers.