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Newsgroups: comp.lang.ada
Subject: Re: Ada Pointer Problem
References: <35f054ea.0410010726.466caebc@posting.google.com>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Fri, 01 Oct 2004 19:24:04 +0200
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Date: 2004-10-01T19:27:20+02:00
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skidmarks writes:
> Each Ptr assignment below yields the following error message:
>
> --    9.    Ptr     : a.X_Ptr  := Object'Access;
> --       non-local pointer cannot point to local object
>
> In the past, the only way that I seem to be able to fix the problem
> is to put the pointer and assignment in global space (either in file
> global or in a package spec). I've looked at Ada as a Second
> Language (Cohen) and, with less diligence, at the Ada LRM but can't
> figure what I'm doing wrong.  What am I doing wrong?

Others have explained the problem, but I think you can solve it by
declaring a local access type (not subtype):

with A;
procedure B is
   type Y is access all A.X; -- local to B

   Object : aliased a.X; -- also local to B

   Ptr : Y := Object'Access;
begin -- B
   null;
end B;

I haven't tried or verified it in the RM, this is just a hint.  But I
think this solution reflects good design; it guarantees that Object
exists for at least as long as type Y.  Thus, you cannot pass Ptr to
subprograms outside of B.

-- 
Ludovic Brenta.