#include <iostream>

using namespace std;

/*  Singleton class */
class Singleton
{

public:
	static Singleton* Instance();
	void printMessage(void);

protected:
	Singleton() {};

private:
	static Singleton* _instance;

};

Singleton* Singleton::Instance() 
{
	if (_instance == 0)
		_instance = new Singleton;
	return _instance;
}
Singleton* Singleton::_instance=0;

void Singleton::printMessage(void)
{
	cout << "Hello world!" << endl;
}

main()
{

	Singleton* theSingleton;

	theSingleton = Singleton::Instance();

	theSingleton->printMessage();



}