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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Make specific warning error with gnat?
Date: Tue, 06 Jul 2010 17:18:00 -0400
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Date: 2010-07-06T17:18:00-04:00
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"Randy Brukardt" <randy@rrsoftware.com> writes:

> Keep in mind that such a message may occur in cases where there is no actual 
> problem.

Right.

>...That can often happen if you have code that is conditional on 
> constants. To take an extreme example, if you have:
>
>       Max_Items := constant := 0;
>
> and then the code is:
>
>      if Max_Items /= 0 then
>           Average := Float(Count)/Float(Max_Items); -- (1)
>      else
>           Average := 0.0;
>      end if;
>
> The code at (1) would raise Constraint_Error if it was executed, but of 
> course it can never be executed. If you change the warning to an error here, 
> you won't be able to compile the code without removing or changing the 
> expression at (1), and that would cause problems if/when Max_Items is set to 
> a different value.

You don't actually need to change (1).  This is what pragma
Warnings(Off) is for.  I don't know if GNAT warns about the
above (I think it might notice that (1) is dead code), but if
it does, tell it to shut up (after carefully making sure the
warning is indeed bogus).

In a case like this, Max_Items is probably declared in some package that
has multiple variants, which are selected by build options (e.g. GNAT
project files).  Of course you need to test all the variants.

You can put Warnings(off/on) around just the one line of code.

- Bob