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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.lang.c++
Subject: Re: Want pointers on intelligent pointers
Message-ID: <12135@pasteur.Berkeley.EDU>
Date: 19 Mar 91 03:45:01 GMT
References: <838@antares.Concordia.CA>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
Lines: 47

In article <838@antares.Concordia.CA>, marcap@antares.concordia.ca ( MARC ANDREW PAWLOWSKY ) writes:
|> I am trying to make a smart class so objects will not delete themselves
|> if someone is pointing to them.
|> 
|> I have been following the discussion so far and came up with
|> the following:
|> 
|> Each object keeps a counter which indicates how many objects
|> are pointing to it. To keep the counter valid it is necessary
|> for the class to have its own copy, and reference routines.

You're close.  But you need two classes, SmartClassRep stores the
actual data and SmartClass stores a pointer to it.  When you copy
SmartClass objects around you adjust the reference count.  Here's
part of the job:

class SmartClassRep {
	friend SmartClass;
	// make all members private
	int refCount;
	SmartClassRep() : refCount(0) { ... }
};

class SmartClass {
private:
	SmartClassRep *p;
public:
	// assignment operator
	SmartClass& operator=(const SmartClass& arg) {
		arg.p->refCount++;
		if (--p->refCount == 0) delete p;
		p = arg.p;
	}
	// copy constructor
	SmartClass(const SmartClass& arg) {
		p = arg.p;
		p->refCount++;
	}
	// destructor
	~SmartClass() {
		if (--p->refCount == 0) delete p;
	}
}

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck