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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Portability questions
Date: 2000/04/25
Message-ID: <wccbt2ycni0.fsf@world.std.com>#1/1
X-Deja-AN: 615462502
Sender: bobduff@world.std.com (Robert A Duff)
References: <3904A339.887711C1@ftw.rsc.raytheon.com>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 2000-04-25T00:00:00+00:00
List-Id: <comp.lang.ada>

Wes Groleau <wwgrol@ftw.rsc.raytheon.com> writes:

> An annotation in the AARM points out that initializations
> are not suppressed by address clauses.

Right.  If you want to avoid default initializations, use pragma Import,
in addition to the address clause.  I think Annex B says something about
that.

> 1. Is there any place in the official RM that says that?
>    (I have used the argument "it says over here that this
>    happens.  It doesn't say there are any exceptions.")

That's the right argument.

After all, how do we know that making a variable name start with Q
doesn't cause initializations to be skipped?  Because the RM doesn't say
otherwise.  ;-)

> 2. How does this apply or not apply to initializations
>    that are NOT required by the language?  For example,
> 
>    type Byte is range 0 .. 255;
>    for Byte'Size use 8;
> 
>    type Buffer is array (Positive range <>) of Byte;
>    pragma Pack (Buffer);
> 
>    B : Buffer (1..Length_Of_Message);
>    for B'Address use Address_Of_Message;
> 
>    -- compiler A fills the space of any declared buffer with
>    -- zeroes.  The language does not require this.  How does
>    -- erasing the received message fit with the Ada 95 rules?

Without pragma Import, the compiler can do what it likes -- initialize B
or not.  I suspect most compilers do not.  I think compilers should not.

With pragma Import on B, I would consider it a bug for a compiler to
initialize B, although I'm not sure I can prove that from the RM.

Then there's pragma Normalize_Scalars, which probably has some effect on
all this.

- Bob