Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!necntc!ima!haddock!karl
From: karl@haddock.ISC.COM (Karl Heuer)
Newsgroups: comp.std.c
Subject: Re: Question about unions
Message-ID: <4278@haddock.ISC.COM>
Date: 27 May 88 22:56:33 GMT
References: <16490002@hpcllz2.HP.COM>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 14

In article <16490002@hpcllz2.HP.COM> walter@hpcllz2.HP.COM (Walter Murray) writes:
>[The dpANS mentions that there may be padding at the end of a structure.]
>Is there any reason a similar statement is not made about unions?
>Section 3.3.3.4 (the sizeof operator) certainly implies that a
>union may have padding.

I don't agree that 3.3.3.4 implies it, but I think that it does have to be
allowed.  The existence of pointers to incomplete types requires that a
word-addressible machine use a consistent format for pointer-to-union
(likewise for pointer-to-struct; this has been expressed as "all struct
pointers smell the same"), and I believe the usual choice for this is word
pointers -- which means that union{char} contains trailing padding.  Looks
like 3.5.2.1 should be reworded to mention unions.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint