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From: "Nick Roberts" <nickroberts@callnetuk.com>
Subject: Re: More C
Date: 2000/02/02
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References: <vhizotrc4x7.fsf@grotte.ifi.uio.no>
 <3896134b@eeyore.callnetuk.com> <vhioga1r2j8.fsf@grotte.ifi.uio.no>
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Date: 2000-02-02T00:00:00+00:00
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Jan's comments broadly accepted.

It surely demonstrates one aspect of the deficiencies of C as a software
engineering language, that the programmer has, in general, no control over
how types are represented, and that it is common for C compilers to vary
from one another (and the ANSI standard) in this matter.

In this respect, it is necessary to think of interfacing Ada source code not
to C source code, but to C object code (i.e. C source as compiled by a
particular version of a particular compiler, with a particular set of flags
in force).

To the rescue, to a certain extent, comes the ability of most C compilers to
output an assembly listing (or other listing) that shows the representations
(and addresses) chosen for types and objects.

--
Nick Roberts
http://www.adapower.com/lab/adaos

"Jan Kroken" <jankr@nntp.ifi.uio.no> wrote in message
news:vhioga1r2j8.fsf@grotte.ifi.uio.no...
> ...
> What if the [C] compiler decides to optimize access to the record,
> so the real memory structure becomes as follows?
>
> for SDL_Color use
>    record
>      Red   at 0  range 0..7;
>      Green at 32 range 32..39;
>      Blue  at 64 range 64..71;
>    end record;
> for SDL_Color'Size use 128;
> ...