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From: pcg@odin.cs.aber.ac.uk (Piercarlo Grandi)
Newsgroups: comp.lang.c++
Subject: Re: how do you define classes that refer to each other ???
Message-ID: <PCG.90Mar23112507@odin.cs.aber.ac.uk>
Date: 23 Mar 90 11:25:07 GMT
References: <49689@wlbr.IMSD.CONTEL.COM>
Sender: pcg@aber-cs.UUCP
Organization: Coleg Prifysgol Cymru
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In-reply-to: mh@awds26.imsd.contel.com's message of 20 Mar 90 00:04:01 GMT

In article <49689@wlbr.IMSD.CONTEL.COM> mh@awds26.imsd.contel.com (Mike Hoegeman) writes:

   This is probably a stupid question, but here goes anyway.  how do you
   set up two classes that refer to each other ?

Another heathen that does not hold my excessively precious advice as
sacred :-)!

If you write all your member functions *after* the class definition, a
lot of problem disappear. You may also need to forward declare the
classes, of course (if you use the typedef style names).

The general scheme is:


	struct c1;	/* forward declarations */
	struct c2;
	struct ...;

	struct c1
	{
		int	m1;
		c2	*m2;

		int	p1(int);

		friend	f1(c2 &,char);
		...
	};

	struct c2
	{
		double	m1;
		c1	m2;

		double	p1(double);

		friend	f2(c2 &,short);
		...
	};

	...

	int	c1::p1(int i) { ... }

	int	f1(c2 &o, char c) { ... }

	double	c2::p1(double d) { ... }

	int	f2(c2 &o,short s) { ... }

	...

Notice that of course you *cannot* have two classes that inherit from
each other or that appear as fields in each other; true recursive
definitions are not allowed.
--
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk