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From: "Pascal Obry" <p.obry@der.edf.fr>
Subject: Re: "out" or "access"
Date: 1998/10/22
Message-ID: <70mo3h$gll$1@cf01.edf.fr>#1/1
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References: <908956499.754394@dedale.pandemonium.fr>
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Newsgroups: comp.lang.ada
Date: 1998-10-22T00:00:00+00:00
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Tucker Taft a �crit dans le message ...
>=:-) Vincent (vb@bruker.fr) wrote:
>: What's the best way ?
>
>An "out" parameter is always preferable to an "access" parameter, in my
view.
>
>Use an "access" parameter only if you need an access value when
>inside the called subprogram for some reason.  This usually only
>happens when interfacing to some other language, or some preexisting
>subsystem of some sort.
>


Ok but be carefull. With an access type you can't pass a null pointer. This
is a big problem.
In fact if you look at the Win32 C API or UNIX C library you'll find that it
is often possible
to pass a null pointer to some parameters to say : "ignore this one, I don't
care for the result" !

So, in many many cases it is better to use an access type (not an access
formal parameter)
when interfacing with some other language.

Pascal.

PS : The Win32Ada binding is full of access parameters that are just wrong !