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From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing with C ; an ununsed fields dilemma
Date: Thu, 2 Jul 2009 03:16:14 -0700 (PDT)
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Date: 2009-07-02T03:16:14-07:00
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On Jul 2, 10:51=A0am, Georg Bauhaus <rm.dash-bauh...@futureapps.de>
wrote:
> Hibou57 (Yannick Duch=EAne) schrieb:
>
>
>
> > Hello to all,
>
> > Once again, a topic about interfacing with C structures.
>
> > A lot of C structure are defined with so called =93 unused field
> > reserved for future use =94 (oftenly never used in any future). This
> > fields are generally to be initialized to zero, what is required, to
> > unsure it will not be errorneously interpreted by the exogenous part
> > of the application, specially if it is dynamically linked to the
> > application (beceause then, its version or its implementation may be
> > differente and unknown of the application which rely on it).
>
> > And here is the dilemma :
>
> > Using clause representation, it is tempting to simply drop this
> > unuseful unusedfields from the visible part of the declaration (yeah
> > dear friend, lot cleaner, really tempting),
>
> Omitting things might be acceptable in mathematical
> discourse, but actually writing things down helps a
> lot in programming, at least it helps me as a reader,
> not up for solving (inter-)language puzzles.
> You explanation of the record's gap fields is itself a hint
> that these components do need some attention.
> Shouldn't therefore Martin's example be the way to go?
>
> This has been discussed before, topics included
>
> =A0 =A0for X use all
> =A0 =A0 =A0 record
> =A0 =A0 =A0 =A0 =A0...
> =A0 =A0 =A0 end record;
>
> pragma Zero_Fill and Unchecked_Conversion (for setting bits to 0);

pragma Zero_Fill sounds interesting...but it isn't standard :-(

Cheers
-- Martin