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From: "Martin Dowie" <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Variant Record Sizes..
Date: Thu, 19 Aug 2004 19:29:51 +0000 (UTC)
Organization: BT Openworld
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Date: 2004-08-19T19:29:51+00:00
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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