Re: Enhancement needed

["Samuel T. Harris" <samuel_t_harris@Raytheon.com>]

Michael Pickett wrote:
> 
> In article <8pol3q$dnqb3$1@ID-25716.news.cis.dfn.de>, Nick Roberts
> <nickroberts@callnetuk.com> writes
> >I'd be grateful if you would mention what it was that you actually wanted
> >your compiler to do, so I can make mine do the same. I'm always eager to
> >please. People seem to think that compiler writers have to be legally
> >coerced into doing anything; some of us will actually respond to a little
> >courtesy. ;-)
> 
> I wasn't the original poster, and I didn't retain the earlier postings,
> 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.

I find that expectation dubious, from whereever it comes.

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
place each field in the appropriate location. I need an address
clause to place the record object at the appropriate place
in memory. I use a size clause as an extra check to ensure
my record layout indeed fits the size of the memory area.
I definately don't want the size clause changing the layout
at all. I expect a warning is the size is too large for the
record and an error if it is too small.

Consider another problem.

I'm interfacing to a C API. I used to use rep clauses on the
records to make them fit, but I now have pragma Convention
in Ada 95 which eliminates all that drudgery. I still use
a size clause to confirm the record will fit into the size
I want. Pragma Convention defines the layout, I don't want
the size clause changing it.

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.

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