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NNTP-Posting-Date: Mon, 05 Feb 2007 19:47:07 -0600
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
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 <BsKxh.1174338$084.631125@attbi_s22>
Subject: Re: C Interface example
Date: Mon, 5 Feb 2007 19:48:31 -0600
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Date: 2007-02-05T19:48:31-06:00
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"Jeffrey R. Carter" <jrcarter@acm.org> wrote in message
news:BsKxh.1174338$084.631125@attbi_s22...
> Maciej Sobczak wrote:
> >
> > What about assigning something to Result and not using Result?
> > That doesn't get through with some pedantic warning switches.
>
> True, you may get a warning, just as you may about not changing To. But
> it's perfectly legal, portable Ada.

Well, it's legal, and it is portable in this case, but it is a bad habit to
get into. (That's why the pedantic warning.) 11.6(5) allows the removal of
code that raises exceptions if the result is not used. I don't think it
applies to external code like C, but it certainly does apply to Ada code.
(And, like all points about 11.6, it's likely to result in a roaring
argument; no one is quite sure what is and is not allowed.)

Anyway, the point is that if you just drop the result on the floor, the Ada
compiler might be allowed to omit the call, too. So it is always best to use
the result somehow. In this case, test it for null and do something
explicit:

    if Result = null then
        raise Internal_Error;
    end if;

where Internal_Error is an appropriately defined exception.

                           Randy.