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From: Jerry <lanceboyle@qwest.net>
Newsgroups: comp.lang.ada
Subject: Re: GNAT 4.2.3 Ubuntu reports weird compile error wrt
	Unchecked_Access
Date: Sun, 17 Aug 2008 14:14:40 -0700 (PDT)
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Date: 2008-08-17T14:14:40-07:00
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On Aug 17, 12:47=A0pm, a...@anon.org (anon) wrote:
> Addition:
>
> The problem is that local data is stored on the primary stack and if an e=
rror
> is encounter the exception handlers could remove the local data off the s=
tack,
> creating a 'dangling references.'. Which would makes the pointer (Access
> variable) invalid or unsafe.
>
> So, you must use the "Unchecked_Access" for local data and the programmer
> is responsible for catching any exceptions or other conditions that might
> cause a 'dangling reference.'
>
> Also, because of the specs refering to "Access" and "Unchecked_Access"
> in both Ada_95 and Ada_2005 is basically unchanged you can use
> "Unchecked_Access" instead of "Access" but be warned you must insure
> the code is safe.
>
> And any GNAT that does not support this type of safety should be concerne=
d
> as corrupt and unusable.
>
> PS. =A0As for Ada-83, the answer is no! =A0"Unchecked_Access" was added
> during the creation of Ada-95.
>
> In <37Ppk.5180$Mh5.1...@bgtnsc04-news.ops.worldnet.att.net>, a...@anon.or=
g (anon) writes:
>

Thanks for clarifying the availability of 'Unchecked_Access across
language versions.

I have a fair grasp of the accessibility rules for access variables
(although I struggle with it sometimes). However, my original post was
not a question of how to use them per se, but about an apparent
compiler error on a particular version of GNAT on Ubuntu.

FWIW, I moved the declaration of Temp_C_String to the same place where
its type is declared and am now able to use 'Access, as in
Temp_C_String'Access. The developer who originally reported the
problem has responded to me that this has allowed the compilation to
progress normally. Given that, I probably won't pursue this too much
farther, but nevertheless, there might be some interest by others in
discovering if this possible compiler mistake is important enough to
chase down and fix.

Jerry