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

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.

Simon Coulter.
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