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From: billjones6789@yahoo.com
Newsgroups: comp.lang.ada
Subject: Re: Bug in Ada (SuSe 10.2) ?
Date: Sat, 23 Feb 2008 02:16:14 -0800 (PST)
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Date: 2008-02-23T02:16:14-08:00
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On Feb 22, 11:21=A0am, Georg Bauhaus <rm.plus-
bug.t...@maps.futureapps.de> wrote:
> On Fri, 2008-02-22 at 08:10 -0800, billjones6...@yahoo.com wrote:
> > Of course, the danger is only eliminated when this language-defined
> > check is fully implemented in standard mode.
>
> Here is another dangling pointer. The program is
> giving me results varying with compiler/OS. I didn't see
> how accessiblity checks could help in this case, but
> then maybe this is a different issue?
>
> with Ada.Unchecked_Deallocation;
> with Ada.Text_IO;
>
> procedure News3 is
> =A0 =A0use Ada;
>
> =A0 =A0type Int_Ptr is access Integer;
> =A0 =A0Pointer: Int_Ptr;
> =A0 =A0Dangling_Pointer: Int_Ptr;
>
> =A0 =A0procedure Copy(Source: in out Int_Ptr; Target: out Int_Ptr) is
> =A0 =A0 =A0 procedure Oops is new Unchecked_Deallocation
> =A0 =A0 =A0 =A0 (Integer, Int_Ptr);
> =A0 =A0begin
> =A0 =A0 =A0 Target :=3D Source;
> =A0 =A0 =A0 Oops(Source);
> =A0 =A0end Copy;
>
> begin
> =A0 =A0Pointer :=3D new Integer'(42);
> =A0 =A0Copy(Pointer, Dangling_Pointer);
>
> =A0 =A0Text_IO.Put_Line(Integer'image(Dangling_Pointer.all));
> end News3;

Yes, this is a different issue, and accessibility checks
unfortunately don't help in this case.  The checks work for
pointers into the stack (objects declared inside subprograms
where 'access is used), not objects allocated on the heap
(where allocators (new) are used).

There are various methods available to detect such errors,
such as using the valgrind tool or special debug storage pools.