Xref: utzoo comp.lang.c:35860 comp.std.c:4252
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From: michi@ptcburp.ptcbu.oz.au (Michael Henning)
Newsgroups: comp.lang.c,comp.std.c
Subject: Save to assign union member to each other ?
Keywords: union, assignment
Message-ID: <315@ptcburp.ptcbu.oz.au>
Date: 6 Feb 91 22:44:45 GMT
Followup-To: comp.lang.c
Organization: Pyramid Technology Corporation
Lines: 34


Something I could not figure out from the various references...

Given

union {
	int	i;
	double	d;
} u;

is it legal to assign one member of the union to another?  Examples:

	u.i = !u.d;
	u.d = (double)u.i;
	u.d = (double)(u.i * 3.14);

The various standard references (K&R, Harbison & Steele) are not clear
about this. Obviously, the address of the lvalue on the left may be the
same as the address of one or more operands in the expression on the right,
as in

	x = -x * x;

But what about the case where the union contains objects of different types
and sizes, as above? It looks legal to me. Has anyone ever encountered a
compiler that generates incorrect code for such a case?

							Michi.

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