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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: ADTs C to Ada
Date: Mon, 5 Mar 2012 07:23:55 -0800 (PST)
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Date: 2012-03-05T07:23:55-08:00
List-Id: <comp.lang.ada>

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

structs cannot contain functions; they can only contain pointers to functio=
ns.  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 =3D s.f(42);
}

-*- Ada -*-
type Function_Pointer is access function (Param : in Integer) return Charac=
ter;
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 :=3D S.F.all (Param =3D> 42);
begin
   null;
end Foo;

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

HTH

--=20
Ludovic Brenta.