Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bbn!apple!rutgers!att!ulysses!andante!alice!shopiro
From: shopiro@alice.UUCP (Jonathan Shopiro)
Newsgroups: comp.lang.c++
Subject: Re: address of virtual function (revisited)
Summary: Pointers to virtual member functions are bound at time of call
Message-ID: <9262@alice.UUCP>
Date: 29 Apr 89 01:47:27 GMT
References: <904@garya.Solbourne.COM>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 66

In article <904@garya.Solbourne.COM>, garya@Solbourne.COM (Gary Aitken) writes:
> Jonathan Shopiro's response to my earlier posting is a help in terms of
> dereferencing the pointers once they have been given the proper values.
> However, I don't see any solution (yet) to the problem of getting the
> proper values in the pointers in the first place.
> 
> How does one get the address of the virtual function for an object, given
> a pointer to the object?
> 
> 	class A {
> 	 public:
> 		virtual	void f() ;
> 	}
> 	class B : public A {
> 	 public:
> 		void	f() ;
> 	}
> 
> 	typedef void A::MEMF() ; // type for "member function of A"
> 	MEMF	*fp ;
> 	B	*bp = new B ;
> 	A	*objp = (A*) bp ;
> 
> ...
> 
> Or am I missing something here?  If I do
> 	fp = &A::f
> and subsequently do a
> 	(bp->*fp)()
> will this somehow go through the virtual table and actually call B::f if
> bp is REALLY a B* object pointer?
It REALLY will.  I promise.

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-- 
		Jonathan Shopiro
		AT&T Bell Laboratories, Warren, NJ  07060-0908
		research!shopiro   (201) 580-4229