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From: gwyn@brl-smoke.UUCP
Newsgroups: comp.lang.c
Subject: Re: Unions that generate offsets (?)
Message-ID: <6424@brl-smoke.ARPA>
Date: Sat, 12-Sep-87 17:07:59 EDT
Article-I.D.: brl-smok.6424
Posted: Sat Sep 12 17:07:59 1987
Date-Received: Sun, 13-Sep-87 08:49:43 EDT
References: <167@jc3b21.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 24
Keywords: union structure offset

In article <167@jc3b21.UUCP> crash@jc3b21.UUCP (Frank (Crash) Edwards) writes:
>Given the following definition, should the reference "msg.m_union.m_from"
>be a legal reference to the member of the "pckt" structure?

No.  You forgot to include ".pckt" in the reference.

>And should
>it reference the first location of m_union or the first location of pckt?

Assuming you fix that, it references the "m_from" member, naturally.

>	"Such constructions are non-portable."

Yup, they were allowed by a particular implementation of C, not by
the language rules.

>First of all, this paragraph should read, "but if preceding member *types*
>differ".

No, K&R had it right.  If preceding members (member names) differ, the
result is non-portable.  Some compilers won't even allow it.

Why don't you just do this the right way (fully-qualified member path),
rather than try to cheat?