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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: C Interface example
References: <1170516037.435847.326440@p10g2000cwp.googlegroups.com>
Date: Sat, 03 Feb 2007 17:15:32 +0100
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Date: 2007-02-03T17:15:32+01:00
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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:

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.