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From: ganesh.ramasivan@gdcanada.com (Ganesh Ramasivan)
Newsgroups: comp.lang.ada
Subject: Re: Variant Record Sizes..
Date: 20 Aug 2004 07:09:28 -0700
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Date: 2004-08-20T07:09:28-07:00
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Thanks a lot for all your suggestions. 

I found that the result is compiler dependent. On the GNAT compiler,
the size of Test_Record is 2 bytes but on the Greenhills Ada compiler,
the result is 4 bytes.

On consulting with Greenhills, they mention the following:

"The size of the record includes the size of the largest variant
part".

This would confirm the results I am getting with the GHS compiler.

Cheers!!

Ganesh


"Martin Dowie" <martin.dowie@btopenworld.com> wrote in message news:<cg2v3f$73h$1@sparta.btinternet.com>...
> Ganesh Ramasivan wrote:
> > Hello,
> >
> > I am having a hard time understanding variant records with regard to
> > memory usage. Does the size of the record become the size of the
> > largest element in that record?
> >
> > So in case of the example below, is the size of the Test_Record 2
> > bytes, even though the "use 8" clause has been specified as the other
> > element of the record specifies "use 16".
> >
> > Any input will be appreciated.
> 
> Couple of things:
>      Test_Record : TEST_ICP_POI_MESSAGE_TYPE(STATE_1);
> 
> Constrains "Test_Record" to always be a subtype of TEST_ICP_POI_MESSAGE_TYPE
> constrained to "STATE_1".
> 
> Because you didn't supply a default value to the descriminant you can never
> change which variant you want Test_Record to be:
> 
> Both these things mean that the compile 'knows' that Test_Record need only
> be 2 bytes long.
> 
> So,
> 
> 1) Add a default to the descriminant if you every what to change which
> variant you want the variable to take; and
> 2) Don't constrain the variable at declaration time.
> 
> Cheers
> 
> -- Martin