Re: C Interface example

[artifact.one@googlemail.com]

On Feb 3, 4:15 pm, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
> artifact.one writes:
> > #ifndef VECTOR_H
> > #define VECTOR_H
>
> > float *vec_addNf(float *, float *, unsigned int);
>
> > #endif
>
> package Vec is
>    type Array_Of_Floats is array (Natural range <>) of Float;
>    function Add (VA     : access Array_Of_Floats;
>                  VB     : in     Array_Of_Floats;
>                  Length : in     Natural)
>       return access Array_Of_Floats; -- Ada 2005 required here
>    pragma Import (C, Add, "vec_addNf");
> end Vec;
>
> but all calls to Add will have to do something with the value
> returned.  Looking at the body of vec_addNf, I see that the returned
> value is useless, since the caller obviously already knows the address
> of VA.  Taking advantage of that fact, we can instead declare a
> procedure:

Yes, the original intent in C was to be able to do this sort of thing:

  vec_addNf(vec_addNf(va, vb), vec_addNf(vc, vd));

...which may or may not be possible or desirable in Ada.

>
> package Vec is
>    type Array_Of_Floats is array (Natural range <>) of Float;
>    procedure Add (VA     : in out Array_Of_Floats;
>                   VB     : in     Array_Of_Floats;
>                   Length : in     Natural);
>    pragma Import (C, Add, "vec_addNf");
> end Vec;
>
> HTH
>
> --
> Ludovic Brenta.

Thanks, that makes things a bit clearer. I'll go with the
procedure definition over the function.

Mc