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From: ark@alice.att.com (Andrew Koenig)
Newsgroups: comp.std.c++
Subject: Re: backward virtual function call
Message-ID: <20292@alice.att.com>
Date: 30 Apr 91 21:15:21 GMT
References: <1991Apr30.024010.4331@csi.uottawa.ca>
Reply-To: ark@alice.UUCP ()
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 31

In article <1991Apr30.024010.4331@csi.uottawa.ca> hitz@sim5.csi.uottawa.ca (Martin Hitz) writes:

> #include <stream.h>

> struct X {
> 	virtual f() { return 1; }
> };

> struct Y : X {
> 	f() { return 2; }
> };

> main()
> {
> 	X x;
> 	Y * y = (Y *) &x;
> 	cout << y->f();
> }

The effects of things like this are undefined.

In this particular example, I expect that many implementations
will print 2, but the assignment

	Y * y = (Y *) &x;

is well-defined only if &x points at an object of class Y --
which, of course, it does not.
-- 
				--Andrew Koenig
				  ark@europa.att.com