Re: Convert between C "void*" pointer and an access

[Victor Porton <porton@narod.ru>]

Randy Brukardt wrote:

> "Victor Porton" <porton@narod.ru> wrote in message
> news:orm3qe$1r0c$1@gioia.aioe.org...
>> What is the right way to convert between C "void*" pointer and an access
>> to
>> a tagged or class-wide type?
> 
> I doubt that there is a *right* way, there just are several possibilities.
> 
>> Ada.Unchecked_Conversion seems to be what I need, but the access type may
>> be
>> "fat" and thus have another format than void*.
> 
> Right, but not very likely. I'd expect this to work in most cases.
> 
> But our solution in the Claw libraries was simply to use the appropriate
> C-convention access type in the interface definitions and avoid making any
> conversions at all. I believe that on the C side, void* and
> <anything-else>* have to use the same representation, so C convention
> should work properly for any pointer type.
> 
> That is, if the C interface contains a void* parameter, we just used an
> appropriate C convention access type in its place in the Ada parameter
> definition. (Using overloading if we needed multiple such pointers - but
> that was very rare.) There's no counterpart to void* in Ada anyway, so one
> has to do something like that in the interfacing definitions.

"- What is your solution for Windows printing problems? - Do not print."

I NEED to convert between access to tagged records (and access to class-wide 
types) and C void* pointers.

I need this because it is C's way to pass objects by using void* and I need 
to pass Ada objects to C functions (not just C objects).

See my other message where I developed a package which is likely to work 
with every Ada compiler (or hopefully even with every conforming Ada 
compiler possible).

-- 
Victor Porton - http://portonvictor.org