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

[Jeffrey Carter <spam@spam.com>]

Dr. Adrian Wrigley wrote:

> Hi folks!
> 
> I have a problem creating a binding to a C library.
> 
> The library makes extensive use of arrays of arrays of structs.
> Both levels of arrays are of variable length.
> 
>  struct node { int index; double value; };
>  struct problem { node **x; };
> 
> When I attempt to define Ada types for this type of thing,
> I find I can't use access types to the arrays with the
> necessary C convention.
> "warning: this access type does not correspond to C pointer"
> is the compiler error.

    -- 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.

-- 
Jeff Carter
"Blessed is just about anyone with a vested interest in the status quo."
Monty Python's Life of Brian
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