Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!snorkelwacker.mit.edu!hsdndev!cmcl2!adm!news
From: ZCCBJSB%EB0UB011.BITNET@cunyvm.cuny.edu (Josep Sau B.)
Newsgroups: comp.lang.pascal
Subject: Type cast byte/word in a record
Message-ID: <26668@adm.brl.mil>
Date: 25 Apr 91 08:17:15 GMT
Sender: news@adm.brl.mil
Lines: 28



Alan mead <amead@s.psych.uiuc.edu> asked about accessing
fields in a record as bytes or as words...

Well, the cleanest way would be using a variant record,
if know in advance that words will be always aligned
in odd or in even bytes, like:

 Ambiguous: RECORD
   CASE BOOLEAN OF
   FALSE :( ByteArr : ARRAY 1..Siz! OF BYTE);
   TRUE  :( WordArr : ARRAY 1..Siz DIV 2! OF WORD);
 END;

But if you need to access to words aligned to any byte, like
Mem and MemW allow, you can simply do a typecast everytime
you need to access (read, assign...) two bytes as a word.
Example:

 Word(Ambiguous.ByteArr1!)  accesses bytes 1 and 2 as a word
 Word(Ambiguous.ByteArr2!)  accesses bytes 2 and 3 as a word
 ...

You have to bother about the order of least and most signifiant
byte in a word, which is 80x8x implementation dependent.

--Josep Sau