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From: "Samuel T. Harris" <samuel_t_harris@Raytheon.com>
Subject: Re: Enhancement needed
Date: 2000/09/18
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Organization: Raytheon Aerospace Engineering Services
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Date: 2000-09-18T00:00:00+00:00
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Ted Dennison wrote:
> 
> "Samuel T. Harris" wrote:
> 
> > Michael Pickett wrote:
> > >
> > > but as far as I recall, the expectation and previous experience was that
> > > setting the Size attribute for a record type should result in the
> > > compiler adjusting, if necessary, the internal layout of the record from
> > > the default layout.
> >
> > Consider the following problem.
> >
> > A memory mapped device provides a collection of data at a specific
> > memory address. I use an Ada record to overlay that address.
> > I need a rather explicit representation clause to exactly
> 
> I believe the entire issue was what the compiler can do in the *absence* of a
> rep clause. Its pretty clear that it needs to honor any record rep clause, or
> die trying. But it was suprising to some that in *absense* of a rep clause,
> compilers still aren't supposed to rearrange record fields to make a size clause
> attainable.
> 

I believe I covered this case in my last paragraph (quoted below) ...

> If all I'm after is a packed version of the record with no
> padding or extra bits, then I expect pragma pack to do the
> job.
> 

... and I also believe we are in agreement. I still expect a size clause
to produce a warning if it is too large and an error if it is too
small but I never expect it to change the layout. That is the purpose
of pragma pack.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"