From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,bb6f4bd169077fb3
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-02-13 08:40:42 PST
Path: 
 archiver1.google.com!news2.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.vmunix.org!newsfeed01.sul.t-online.de!newsmm00.sul.t-online.com!t-online.de!news.t-online.com!not-for-mail
From: "Martin Krischik" <Martin.Krischik@T-Online.de>
Newsgroups: comp.lang.ada
Subject: Re: Representing data differently
Date: Wed, 12 Feb 2003 19:52:27 +0100
Organization: never organized
Message-ID: <pan.2003.02.12.18.52.25.30761@T-Online.de>
References: <686be06c.0302070615.3943b629@posting.google.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-15
X-Trace: news.t-online.com 1045154297 03 21709 t7ngE1CVTdYq3l 030213 16:38:17
X-Complaints-To: abuse@t-online.com
X-Sender: 05341395658-0001@t-dialin.net
User-Agent: Pan/0.13.0 (The whole remains beautiful)
Xref: archiver1.google.com comp.lang.ada:34060
Date: 2003-02-12T19:52:27+01:00
List-Id: <comp.lang.ada>

On Fri, 07 Feb 2003 06:15:18 +0000, Daniel Allex wrote:

> In C I can represent the same data multiple ways using structs and
> unions.  How and can I do this in Ada?  See example below:
> 
> //
> // Example of C's representation clause
> //
> struct MT_37_header
> {
>     short
> 		:4,
> 		nw:6,
> 		mt:6;
>     short
> 		:16;		// place holder
>     short
> 		:16;		// place holder
>     short
>  		:16;		// place holder
> };

Since it is quite dangerous you have to do a lot of typing:

-- snip
    type
        State
    is record
        uninitialized    : Boolean ;
        on               : Boolean ;
        writeLineNumber  : Boolean ;
        writePrefix      : Boolean ;
    end record;

    for
        State
    use record
        uninitialized   at 0 range 0..0;  
        on              at 0 range 1..1;    
        writeLineNumber at 0 range 2..2;   
        writePrefix     at 0 range 3..3;   
    end record;

-- snap

The first statement defines the record, the second defines the layout.
Nothing stops you from placing two record elements at the same position.

with regards

Martin

PS: If you like you can look at the rest of the (unfinished) source as well:

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/adacl/adacl/Include/AdaCL-Trace.adb

-- 
Martin Krischik
mailto://Martin@krischik.com
http://www.martin.krischik.com