Re: C bindings, Interfaces.C.Pointers etc.

["Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk>]

On Tue, 11 May 2004 18:48:57 +0000, Jeffrey Carter wrote:

>     -- struct node { int index; double value; };
>     type Node_Info is record
>        Index : Interfaces.C.Int;
>        Value : Interfaces.C.Double;
>     end record;
>     pragma Convention (C, Node_Info);
> 
>     -- struct problem { node **x; };
>     type Node_Ptr     is access all Node_Info;
>     pragma Convention (C, Node_Ptr);
>     type Node_Ptr_Ptr is access all Node_Ptr;
>     pragma Convention (C, Node_Ptr_Ptr);
>     type Problem_Info is record
>        X : Node_Ptr_Ptr;
>     end record;
>     pragma Convention (C, Problem_Info);
> 
> This compiles fine. This is an exact duplicate of the C declarations. To 
> deal with this using a higher level Ada abstraction, you'd wrap 
> something around this to provide that abstraction.

I hadn't thought of doing this - it doesn't seem to provide easy answers
for allocation and indexing though.  In this application, I am building
data structures for use by a C/C++ library.  The wrapper you're
suggesting (I guess) is for accessing elements of the arrays,
and allocating/freeing them.  I'd have to check that the additional
code didn't impose excessive overheads.

The solution I have adopted in the end is based on my idea (4),
mentioned by tmoran and Martin Chrischik (see other messages).

Thanks!
-- 
Adrian