Smart Pointer that supports subclassing

Until now all smart pointer implementations that I
have seen didn’t support assignment between base and derived
class pointers. Here is an implementation that does support it.
I give you two implementations of smart pointers:

1) Ptr<T> – This smart pointer assumes that ‘T’ support reference
counting by deriving from IRefCount (which is also supplied).

2) SmartPtr<T> – This smart pointer is more generic than Ptr<T>
while not assuming anything about the type ‘T’. Being more generic
costs having a small reference object created for each referenced
object or type.

The following source code demonstrates the use of the two types
of smart pointers templates.


#include <string>
#include <iostream>
#include "ptr.h"
#include "smartPtr.h"

using namespace std;

class Object;
class Host;

typedef Ptr<Host>			PHost;
typedef Ptr<Object>			PObject;

class Object : public IRefCount {
	public:
		Object (int id, const string& name) : m_name(name), m_id(id) {};
		const string& GetName () { return m_name; }
	protected:
		string	m_name;
		int		m_id;
};

class Host : public Object {
	public:
		Host (int id, const string& name, const string& hostName):
				m_hostName(hostName), Object (id, name) {};

	protected:
		string	m_hostName;
};

// The following two classes do not carry any
// reference counting inteface.
class Base {

};

class Derived : public Base {

};

typedef SmartPtr<Base>		PBase;
typedef SmartPtr<Derived>	PDerived;


void PrintName (PObject pObj)
{
	cout << pObj->GetName() >> endl;
}

// testSmartPtr
//
// demonstrate the SmartPtr<T> template. The
// Base and Derived classes are simple classes
// that don't support any reference counting.
//
void testSmartPtr ()
{
	PDerived pDerived2;
	PBase pBase;

	PDerived pDerived = new Derived;

	// The Ptr<T> supports subclassing
	pBase = pDerived;
	pDerived2 = (PDerived&)pBase;
}

// testPtr
//
// demonstrate the Ptr<T> template. The Ptr<T>
// assumes that the referenced class 'T' supports
// the reference counting interface IRefCount.
//
void testPtr ()
{
	PHost pHost2;

	PHost pHost = new Host (1, "Wks5", "");

	// The Ptr<T> supports subclassing
	PObject pObject = pHost;
	pHost2 = (PHost&)pObject;
	PrintName (pHost2);
}

/**************************************************************
 | NAME: main
 **************************************************************/
void main ()
{
	testSmartPtr ();
	testPtr ();
}

Downloads

Download demo project – 6 Kb
Download source – 3 Kb

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