Re: Interfacing to C non-void procedure with "out" parameters

[Ted Dennison <dennison@telepath.com>]

In article <85nqaf$95o$1@nnrp1.deja.com>,
  Jeff Carter <jrcarter001@my-deja.com> wrote:
> In article <85ngl3$10s$1@nnrp1.deja.com>,
>   Ted Dennison <dennison@telepath.com> wrote:
> > First you interface to the routine to create your thin binding:
> >
> >    function esGetValue (Key   : in Interfaces.C.Int;
> >                         Value : in System.Address
> >                        ) return Interfaces.C.Int;
> >    pragma Import (C, esGetValue, "esGetValue");
> There's no reason to use System.Address here. Use an access parameter:

If you mean doing a "Value : access Interfaces.C.Int", that is sometimes
doable. The problem with that is than many C interfaces, particularly
system calls, have optional pointer parameters where "null" is an
acceptable value. An access parameter does not allow "null" to be passed
in. So in general they aren't always useful

> >         esGetValue
> >           (Key   => Interfaces.C.Int(Key),
> >            Value => Value
> >           ) = 0
>
> Note that the call here should not compile; Value is not of type

Yikes! You're right. It should read:
esGetValue
  (Key   => Interfaces.C.Int(Key),
   Value => Value'address
  ) = 0

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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