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From: vladimir@speedy.intrepid.com (Vladimir Vukicevic)
Newsgroups: comp.lang.ada
Subject: Re: C++ to Ada95, help please
Date: 24 Mar 1995 09:07:28 GMT
Organization: Intrepid Technology, Inc.
Message-ID: <VLADIMIR.95Mar24010728@speedy.intrepid.com>
References: <3kjd2m$d3t@jerry.rb.icl.co.uk>
 <SAL714.95Mar23130133@rs710.gsfc.nasa.gov>
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In-reply-to: sal714@rs710.gsfc.nasa.gov's message of 23 Mar 1995 18:01:33 GMT
Date: 1995-03-24T09:07:28+00:00
List-Id: <comp.lang.ada>

In article <SAL714.95Mar23130133@rs710.gsfc.nasa.gov> sal714@rs710.gsfc.nasa.gov (Stephen A. Leake) writes:

: type DISCRIMINANTS is (One, Two);
: for DISCRIMINANTS use (One => ?, Two => ?);
: type struct_STRUCT_NAME (item1 : DISCRIMINANTS) is
: record
: 	case item1 is
: 	when One =>
: 		u_item1 : int;
: 	when Two =>
: 		u_item2 : int;
: 	end case;
: 	item2 : int
: end record;
: 
: If item1 (or item2) is not used in this way, there is no direct Ada
: equivalent structure (and the C code is not very good!).

Of course, a representation clause for the record is needed above, as
there are no guarantees that the Ada compiler will arrange this record
in memory to correspond to the C struct/union. Something like the following
is needed:

for struct_STRUCT_NAME use
	record
		item1 at 0 range 0 .. 7;
		u_item1 at 1 range 0 .. 7;
		u_item2 at 1 range 0 .. 7;
		item2 at 2 range 0 ..7;
	end record;

Note that, because of 13.5.1 (11), you can't just define a record rep
clause with overlapping components; they must be distinct variants.

	- Vladimir