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 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: a07f3367d7,fa8a8653458b3e4b
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news1.google.com!npeer01.iad.highwinds-media.com!feed-me.highwinds-media.com!cyclone01.ams2.highwinds-media.com!news.highwinds-media.com!npeersf02.ams.highwinds-media.com!newsfe15.ams2.POSTED!40385e62!not-for-mail
From: Per Sandberg <per.sandberg@bredband.net>
User-Agent: Thunderbird 2.0.0.22 (Windows/20090605)
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: using the 'use at' feature inside a record?
References: 
 <8f6142f2-ea37-46d7-a29c-0498da5dd9da@t13g2000yqn.googlegroups.com>
In-Reply-To: 
 <8f6142f2-ea37-46d7-a29c-0498da5dd9da@t13g2000yqn.googlegroups.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Message-ID: <%c%pm.68767$Ne3.5147@newsfe15.ams2>
X-Complaints-To: abuse@WWWSpace.NET
NNTP-Posting-Date: Thu, 10 Sep 2009 04:25:31 UTC
Date: Thu, 10 Sep 2009 05:17:33 +0200
Xref: g2news2.google.com comp.lang.ada:8266
Date: 2009-09-10T05:17:33+02:00
List-Id: <comp.lang.ada>

Well there are always unchecked unions:
    "ARM B.3.3 Pragma Unchecked_Union"
---------------------------
    type foo (dummy : Integer := 0) is record
       case dummy is
       when 1 =>
          as_integer              : integer;
       when 2 =>
          as_float                : Short_Float;
       when 3 =>
          as_String               : String (1 .. 4);
       when others =>
          as_Stream_Element_Array : Ada.Streams.Stream_Element_Array (1 
.. 4);
       end case;
    end record;
    pragma unchecked_Union(foo);
---------------------------

The above construct will is an exact equivalent of C's unions.

/Per


PForan wrote:
> Hi all,
> 
> I have a question about the "use at" feature and how it can be used
> inside a record to simulate C's unions. I often have an array of
> bytes, as well as a string which is "use at"'ed on top of the byte
> buffer, very useful as I can play with the data in any way I choose.
> i.e.
> 
> byte_buf: array(1..100) of unsigned_8;
> str_buf: string(1..100);
> for str_buf use at byte_buf'address;
> 
> Is it possible to have something like this within a record?
> 
> TIA,
> Phil