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From: "Egil H. H�vik" <egil.harald.hoevik@REMOVEkongsberg.com>
Newsgroups: comp.lang.ada
References: <2ph6fjFkpsahU1@uni-berlin.de>
Subject: Re: Interfacing with C: access/out parameters
Date: Tue, 31 Aug 2004 09:54:51 +0200
Organization: Kongsberg Defence & Aerospace
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Date: 2004-08-31T09:54:51+02:00
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"Jano" <notelacreas@porfavor.no> wrote in message
news:2ph6fjFkpsahU1@uni-berlin.de...
> Hi,
<snip>
>
> function Blah (Datum : access Data) return C.Int;
> pragma Import (C, Blah);
>
>
> Procedure Ada_Blah (Datum : out Data);
> -- May raise some exception
>
> And my doubt, finally, is: can I ensure somehow that Datum is passed by
> reference?, so I can do inside Ada_Blah [1]:
>
> Helper : aliased Datum;
> For Helper'Address use Datum'Address;
> if Thin_Package.Blah (Helper'Access) = Error_Value then
>     raise My_Error;
> end if;
>

Well, you say Data is a record type, so what's wrong with:

procedure Ada_Blah( Datum : out Data ) is
   function Blah( Datum : Data ) return C.int;
   pragma Import( C, Blah );
begin
   if Thin_Package.Blah(Datum) = Error_Value then
      raise My_Error;
   end if;
end Ada_Blah;


B.3(65): "An Ada function corresponds to a non-void C function"
B.3(69): "An Ada parameter of a record type T, of any mode, is passed as a
t* argument
   to a C function, where t is the C type corresponding to the Ada type T."


~egilhh