Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site druxu.UUCP
Path: utzoo!linus!vaxine!wjh12!genrad!grkermit!masscomp!clyde!burl!ulysses!mhuxl!ihnp4!drutx!druxu!tll
From: tll@druxu.UUCP
Newsgroups: net.lang.c
Subject: Re: C structure alignment
Message-ID: <1051@druxu.UUCP>
Date: Wed, 11-Apr-84 20:59:30 EST
Article-I.D.: druxu.1051
Posted: Wed Apr 11 20:59:30 1984
Date-Received: Fri, 13-Apr-84 01:49:37 EST
References: <122@ihnet.UUCP>
Organization: AT&T Information Systems Laboratories, Denver
Lines: 23

>From: tjr@ihnet.UUCP (Tom Roberts)
>
>It is NOT PORTABLE to assume the ordering of members within a structure,
>nor to assume they are contiguous in memory.

It's true that members may not be contiguous in memory, but (time for
the bible-thumping quote from The C Reference Manual, p196)

	"Within a structure, the objects declared have addresses which
	increase as their declarations are read left-to-right."

So the ordering is clearly defined.  This feature is useful when you
need to store a large number of structures that have differing amounts
of data in them (for instance, in a circuit simulator, you might want a
structure for each component -- early in the structure, you define what
kind of component this is, and the rest of the structure is optimized
for the particular component).  A union could be used, but then you use
the maximum amount of storage for each structure, which may be more than
you have.

		Tom Laidig
		AT&T Information Systems Laboratories, Denver
		...!ihnp4!druxu!tll