Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!uupsi!sunic!dkuug!diku!thorinn
From: thorinn@diku.dk (Lars Henrik Mathiesen)
Newsgroups: comp.lang.c
Subject: Re: Save to assign union member to each other ?
Keywords: union, assignment
Message-ID: <1991Feb8.184517.14109@odin.diku.dk>
Date: 8 Feb 91 18:45:17 GMT
References: <315@ptcburp.ptcbu.oz.au>
Sender: news@odin.diku.dk (Netnews System)
Organization: Department of Computer Science, U of Copenhagen
Lines: 23

michi@ptcburp.ptcbu.oz.au (Michael Henning) writes:
>Given

>union {
>	int	i;
>	double	d;
>} u;

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

Under Semantics of 3.3.16.1 (Simple assignment), the C Standard says:

"If the value being stored in an object is accessed from another object
 that overlaps in any way the storage of the first object, then the
 overlap shall be exact and the two objects shall have qualified or
 unqualified version of a compatible type; otherwise the behavior is
 undefined."

The answer to your question is no.

--
Lars Mathiesen, DIKU, U of Copenhagen, Denmark      [uunet!]mcsun!diku!thorinn
Institute of Datalogy -- we're scientists, not engineers.      thorinn@diku.dk