Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!huxley!glenn
From: glenn@bitstream.com (Glenn P. Parker)
Newsgroups: comp.lang.c++
Subject: Re: cast of a bound pointer: why ?
Message-ID: <GLENN.91Jun13111753@huxley.huxley.bitstream.com>
Date: 13 Jun 91 15:17:53 GMT
References: <1991Jun11.191016.9873@beaver.cs.washington.edu> <763@taumet.com>
	<1991Jun12.180414.16718@beaver.cs.washington.edu>
	<1991Jun12.192101.20607@Think.COM>
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Reply-To: <glenn@bitstream.com> (Glenn Parker)
Distribution: comp
Organization: Bitstream, Inc.
Lines: 51
In-reply-to: barmar@think.com's message of 12 Jun 91 19:21:01 GMT

In article <1991Jun12.192101.20607@Think.COM> barmar@think.com (Barry Margolin) writes:
> In article <1991Jun12.180414.16718@beaver.cs.washington.edu> pauld@stowe.cs.washington.edu (Paul Barton-Davis) writes:
> >This is the heart of the matter. C++ assumes that EVERY function
> >*requires* a "this" pointer. 
> 
> No, only member functions.

Close.  Only non-static member functions require a "this" pointer.

> >Any ideas on how one would do this if it were not possible (as it
> >currently is) to obtain the actual address of a member function ?
> >I have a few ideas myself, but would like to see some others if there
> >are any.

It *is* possible to take the address of a static member function.

> Any problem (except efficiency, maybe) in computer science can be solved by
> adding enough levels of indirection.
> 
> In this case, define a non-member function that takes the class object as a
> regular argument and simply invokes the member function, and pass the
> address of this non-member function.  The non-member function would look
> something like this:
> 
> int nonmember_fn (my_class object, int arg1, char *arg2) {
> 	return object.member_fn (arg1, arg2);
> }

Or, define a static member function, and let it do all the work.
Like so:

    class foo
    {
      public:
        // Don't confuse the following "static" with file static linkage.
	static int bar(foo*, int arg1, char* arg2);
      private:
	int baz;
    };

    int foo::bar(foo* self, int arg1, char* arg2)
    {
	// Use self->baz to access private data member.
    }

The address of foo::bar is &foo::bar.

--
Glenn P. Parker       glenn@bitstream.com       Bitstream, Inc.
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