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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Character/Integer Conversion
Date: 2000/04/03
Message-ID: <8cajks$d71$1@nnrp1.deja.com>#1/1
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Date: 2000-04-03T00:00:00+00:00
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In article <8ca7k8$v2q$1@nnrp1.deja.com>,
  David C. Hoos, Sr. <david.c.hoos.sr@ada95.com> wrote:

> I do this all the time, in the following way:
> Msg : String (1 .. Length);
> type Msg_Bytes is array (Msg'Range)of
>       Interfaces.C.Unsigned_Char;
> use type Interfaces.C.Unsigned_Char;
> Msg_Overlay : Msg_Bytes;
> for Msg_Overlay'Address use Msg'Address;

One more point about the above dubious code.

There is no guarantee that the declaration of Msg_Overlay
will not clobber the valeu in Msg. This probably will not
affect anything, but in other cases it can. It is probably
a good idea to always use a pragma Import (Ada, ..) for
the variable doing the overlaying to inhibit any default
initialization associated with the variable.

For example, in

   x : integer := f (x);
   y : access_to_integer;
   for y'address use x'address;

the declaration of y will likely clobber the initial value
of x, and we should prevent that by either writing:

   x : integer := f (x);
   y : access_to_integer;
   for y'address use x'address;
   pragma Import (Ada, y);

or better by not using address overlays (an unchecked conversion
would be far safer and clearer in this situation).





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