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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Objective C
Date: Sat, 21 Nov 2015 03:31:18 -0800
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Robert Wessel <robertwessel2@yahoo.com> writes:
[...]
> And, of course, writing to one union member and reading from the other
> is undefined.

Incorrect.

N1570 6.5.2.3p3, footnote:

    If the member used to read the contents of a union object is
    not the same as the member last used to store a value in the
    object, the appropriate part of the object representation of
    the value is reinterpreted as an object representation in the
    new type as described in 6.2.6 (a process sometimes called
    "type punning"). This might be a trap representation.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"