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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Bug in Ada (SuSe 10.2) ?
Date: Fri, 22 Feb 2008 16:39:08 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2008-02-22T16:39:08-05:00
List-Id: <comp.lang.ada>

Vadim Godunko <vgodunko@gmail.com> writes:

> On 22 ���, 22:21, 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
>>    use Ada;
>>
>>    type Int_Ptr is access Integer;
>>    Pointer: Int_Ptr;
>>    Dangling_Pointer: Int_Ptr;
>>
>>    procedure Copy(Source: in out Int_Ptr; Target: out Int_Ptr) is
>>       procedure Oops is new Unchecked_Deallocation
>>         (Integer, Int_Ptr);
>>    begin
>>       Target := Source;
>>       Oops(Source);
>>    end Copy;
>>
>> begin
>>    Pointer := new Integer'(42);
>>    Copy(Pointer, Dangling_Pointer);
>>
>>    Text_IO.Put_Line(Integer'image(Dangling_Pointer.all));
>> end News3;
>
> Unchecked_Deallocation never makes program less erroneous. In the
> example it is safe to remove instantiation of Unchecked_Deallocation.
> Allocated memory will be automatically reclaimed after control flow
> leave News3 subprogram, independent does or doesn't it is a main
> subprogram.

An implementation is allowed to do such reclamation, but most do not,
unless you add a Storage_Size or Storage_Pool clause.

- Bob