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Date: Thu, 02 Jul 2009 11:51:46 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Subject: Re: Interfacing with C ; an ununsed fields dilemma
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Date: 2009-07-02T11:51:47+02:00
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Hibou57 (Yannick Duch�ne) schrieb:
> Hello to all,
> 
> Once again, a topic about interfacing with C structures.
> 
> A lot of C structure are defined with so called � unused field
> reserved for future use � (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

   for X use all
      record
         ...
      end record;

pragma Zero_Fill and Unchecked_Conversion (for setting bits to 0);