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Path: utzoo!utgpu!water!watnot!watmath!mks!wheels
From: wheels@mks.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: Type coercion
Message-ID: <245@mks.UUCP>
Date: Mon, 6-Apr-87 08:20:50 EST
Article-I.D.: mks.245
Posted: Mon Apr  6 08:20:50 1987
Date-Received: Mon, 6-Apr-87 23:46:37 EST
References: <2499@dalcs.UUCP>
Organization: Mortice Kern Systems, Waterloo, Ont.
Lines: 26
Keywords: C, Modula-2, long, int, conversion
Summary: what about alignment?

In article <2499@dalcs.UUCP>, silvert@dalcs.UUCP (Bill Silvert) writes:
 > Type coercion in this case means putting both formulations in the same
 > location by using a union:
 > 
 > 	union { long datetime;
 > 		structure { int date;
 > 			    int time;
 > 			  } pair
 > 		} trick;
 > 
 > (apologies if I haven't got the syntax quite right)
 > 
 > I have used this in my own datesetting program and find it convenient,
 > but wonder if it creates problems with other compliers and languages.
 > Clearly this usage assumes that structures are stored

I haven't used unions much, but isn't it true that C may attempt to
re-align the items within a structure (or union) to lie on proper
boundaries (e.g. word boundaries, longword boundaries, etc) where
necessary? This means that there may be padding bytes within the
structure. Could this cause errors where the elements of the structures
within the union don't lie "on top of one another" as one would
expect?
-- 
Gerry Wheeler                  {seismo,decvax,ihnp4}!watmath!mks!wheels
Mortice Kern Systems Inc.