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From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: win32ada design question/problem
Date: 1998/11/17
Message-ID: <36519A6A.C07508F5@elca-matrix.ch>#1/1
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References: <364C5EDE.4F402D13@elca-matrix.ch>
 <72i3r9$o1r$1@nnrp1.dejanews.com> <ubtm7cxj0.fsf@gsfc.nasa.gov>
 <72s2as$pbg$1@nnrp1.dejanews.com>
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Reply-To: Mats.Weber@elca-matrix.ch
Newsgroups: comp.lang.ada
Date: 1998-11-17T00:00:00+00:00
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dennison@telepath.com wrote:
> 
> In article <ubtm7cxj0.fsf@gsfc.nasa.gov>,
>   Stephen Leake <Stephen.Leake@gsfc.nasa.gov> wrote:
> >
> > While I agree it wasn't well designed, I don't agree you need to go to
> > a thick binding. The binding should use 'out' parameter modes in the
> > places where C uses pointers to achieve output parameters. Most
> > compilers will map an 'out' parameter to a C pointer, since that's
> > what 'by reference' means.
> 
> Actually, according to B.3(68), that is *required* behavour. The problem with
> that technique is that many C routines attach a signifigance to a incomming
> value of null. You won't be able to produce such a value on the Ada side, so
> some of the functionality of the C routine will be lost.

And there is another, more severe problem. The C function may allocate
some memory that you must free later, e.g.

procedure P (X : out Some_Record_Type);
pragma Import(C, P);

now as you have no pointer to the returned data, you cannot free it.

I think the Ada 83 classic int + System.Address approach is better in
this case.