Re: How to import C pointers to structures?

[Adam Beneschan <adambeneschan@gmail.com>]

On Monday, May 19, 2014 5:10:14 PM UTC-7, Shark8 wrote:
> On 19-May-14 16:44, Adam Beneschan wrote:
> 
> >> You generally *can't*  do a real/meaningful import w/o knowing the
> >> layout.
> 
> > I'm not sure that's quite true ... there are lots of situations
> > where you simply want to "pass through" a pointer, e.g. in
> > callback situations, where a function sets up a callback and says
> > "when you do the callback, please pass this pointer to it"; and
> > whoever registers the callback will take the pointer, store it
> > somewhere, and use it when it's needed, without ever trying to
> > look at what it points to.
> 
> While those are /common/ cases, I would be hesitant to call them 
> /general/ cases.
> 
> > Unfortunately, I don't see the equivalent of "void *" anywhere in
> > Interfaces.C, which is what the sort of thing you'd want.  You
> > could probably use Interfaces.C.Strings.chars_ptr (the equivalent
> > of "char *").
> 
> Instantiate Interfaces.C.Pointers on a null-record or, perhaps, 
> System.Address?

I wouldn't trust System.Address; there's no guarantee that the Ada implementation of this Ada type is represented the same way as a C pointer, an Ada access object, or anything else.  The first idea, to instantiate Interfaces.C.Pointers, should be trustworthy--that's an excellent idea.

                               -- Adam