/*
 * singleton.cpp
 *
 * Singleton example.  Ensure a class has only one instance
 * and provide a global point of access.
 */

#include <iostream>

class Singleton {

public:

  static Singleton* instance() {

    if (_instance == 0)
      _instance = new Singleton();

    return _instance;
  }

  ~Singleton() { if (_instance != 0) delete _instance; }

  void operation() {
    std::cout << "Singleton " << this << "\n";
  }

protected:
  Singleton() {};

private:
  static Singleton* _instance;
};

// Static variable definition would be in the .cpp file.
Singleton* Singleton::_instance = 0;

int main() {

  Singleton* s1 = Singleton::instance();
  s1->operation();

  Singleton* s2 = Singleton::instance();
  s2->operation();
}