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From: poser@csli.Stanford.EDU (Bill Poser)
Newsgroups: comp.lang.c
Subject: Re: casting to a union
Message-ID: <11426@csli.Stanford.EDU>
Date: 13 Dec 89 07:42:04 GMT
Sender: news@csli.Stanford.EDU
Reply-To: poser@csli.stanford.edu (Bill Poser)
Organization: Center for the Study of Language and Information, Stanford U.
Lines: 9

Perhaps the simplest point to note about why  (union numstr) 7
is no good is to keep in mind that unions really are aggregates.
It is easy to fall into the trap of thinking of a union as a type
abstraction, so that a union that can hold either a character point
or an integer is a type that is one or the other, but that isn't
the case from C's point of view. Rather, a union is an aggregate
just like a struct except for the fact that the members share storage.
So the reason you can't cast 7 to (union numstr) is the same reason that
you can't cast it to a struct or an array.