Observer Pattern

///////////////////////////////////////////////////
// File   : - ObserverPattern.h
// Author : - Nilesh K. Karkhanis
//

#include <list>

using namespace std;

//////////////////////////////////////////////////////
// Client class who is interested in getting notification 
// when the observerable changes
//
class Client
{
public:
	Client() { cout << endl << "C'tor Client"; }
	~Client() { cout << endl << "D'tor Client "; }
	void Update() { cout << "Update" << endl; }
};

//////////////////////////////////////////////////////
// Observer class which monitors the changes of observerable
// and notifies the client of any change
//
class Observer
{
public:
	Observer() { cout << endl << "C'tor Observer ";myClient.erase(myClient.begin(), myClient.end()); }
	~Observer();
	bool Attach(Client* );
	bool Detach(Client* );
	void Notify( );

private:

	list<Client*> myClient;
};

//////////////////////////////////////////////////////
// Class that is to be observered
//
class Observerable
{
public:
	Observerable() { cout << endl << "C'tor Observerable "; myObserver = NULL; }
	~Observerable() {cout << endl << "D'tor Observerable "; }

	bool SetObserver(Observer* apObserver ) 
	{
		if ( !apObserver )
			return false;

		myObserver = apObserver; 

		return true;
	}

	void StateChanged( ) 
	{
		cout << endl << "State Changed";
		myObserver->Notify();
	}

private:
	Observer* myObserver;
};