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: a07f3367d7,36c197595b07e443
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news2.google.com!news.glorb.com!feeder.erje.net!news.mixmin.net!aioe.org!not-for-mail
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Cross-platform issues
Date: Tue, 8 Dec 2009 00:33:04 +0000 (UTC)
Organization: Aioe.org NNTP Server
Message-ID: <hfk6s0$vn7$1@aioe.org>
References: <hfhf9l$2gh$1@news.albasani.net>
NNTP-Posting-Host: +ERTOT2Y9KJRZ8n+NpAZGA.user.aioe.org
X-Complaints-To: abuse@aioe.org
X-Notice: Filtered by postfilter v. 0.8.0
X-Newsreader: Tom's custom newsreader
Cancel-Lock: sha1:1WHbWF3dsZGPRaZv6DmRlmYMa4I=
Xref: g2news1.google.com comp.lang.ada:8342
Date: 2009-12-08T00:33:04+00:00
List-Id: <comp.lang.ada>

> closely as possible to the one that inspired it.  The original
> emits trace data with things like field length info in 4-byte
> integers, for example. I suppose that using a derived type to
> ensure that in my implementation those fields conform with the
> original is one way to do it, but is that accepted practice, or
> is there a more usual one?
  Representation clauses and pragmas let you specify machine
characteristics, for instance that a particular field is 4 bytes long.
Types, and derived types, generally have to do with the logical nature of
the data
eg
type Field_Lengths is range 1 .. 64;
type Water_Temperatures is range 32 .. 212;
type Car_Mileages is range 0 .. 400_000;
etc
An item of any of those types would fit in a four byte field, even
though the first two types could fit in a single byte.  In the absence
of a representation clause, the compiler is allowed to choose whatever
it likes.  If you want something *represented* the same on two different
machines, or via two different compilers, use representation clauses.