Re: ADTs C to Ada

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Patrick wrote on comp.lang.ada:
> I am studying Ada and making progress. The C interface seems straight forward enough for functions, strings pointers and such but I am having trouble finding any information on how to interface with stucts that contain functions.

structs cannot contain functions; they can only contain pointers to functions.  You can call the pointed-to functions from Ada like this:

-*- C -*-
typedef char (*function_pointer_t) (int);
struct struct_t {
   function_pointer_t f;
};
void foo(struct struct_t s) {
  char result = s.f(42);
}

-*- Ada -*-
type Function_Pointer is access function (Param : in Integer) return Character;
pragma Convention (C, Function_Pointer);

type Struct is record
   F : Function_Pointer;
end record;
pragma Convention (C, Struct);

procedure Foo (S : in Struct) is
   Result : Character := S.F.all (Param => 42);
begin
   null;
end Foo;

If you are really interfacing with C++, where structs can contain "member functions", then you need to delve into the C++ interfacing which is specific to GNAT.  The compiler must learn about the vtable of the imported structs, about their constructors and destructors, etc.

HTH

-- 
Ludovic Brenta.