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From: sal714@rs710.gsfc.nasa.gov (Stephen A. Leake)
Newsgroups: comp.lang.ada
Subject: Re: C++ to Ada95, help please
Date: 23 Mar 1995 18:01:33 GMT
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Message-ID: <SAL714.95Mar23130133@rs710.gsfc.nasa.gov>
References: <3kjd2m$d3t@jerry.rb.icl.co.uk>
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In-reply-to: skj@rb.icl.co.uk's message of 20 Mar 1995 08:06:46 -0000
Date: 1995-03-23T18:01:33+00:00
List-Id: <comp.lang.ada>

In article <3kjd2m$d3t@jerry.rb.icl.co.uk> skj@rb.icl.co.uk (Simon
Johnston) writes:

In article <3kjd2m$d3t@jerry.rb.icl.co.uk> skj@rb.icl.co.uk (Simon
Johnston) writes:



   typedef struct _STRUCT_NAME {.....type struct_STRUCT_NAME is
   ....................................record
     int item1;..........................item1  : int;
     union {                             :
       int  u_item1;                     :
       long u_item2;                     :
     } u_name;                           :
     int item2;..........................item2  : int;
   ....................................end record;
   } STRUCT_NAME;....................type STRUCT_NAME is new struct_STRUCT_NAME;

The Ada (near) equivalent of a C union is a variant record, but you
need a discriminant. I'll assume item1 is used as a discriminant in
the C structure (good C code does include discriminants); that is, the
value of item1 tells you whether to use u_item1 or u_item2. Then the Ada
equivalent is:

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!).

- Stephe
--
Stephen Leake, NASA Goddard Space Flight Center
email: Stephen.Leake@gsfc.nasa.gov