C++ Code Example: Singleton Class (Ex:5)

Sphere: Related Content #include <iostream>
using namespace std;

class Singleton
{
  public:
    static Singleton* Instance();
    int printMessage() {cout << "hi......\n";}
  protected:
    Singleton();
    Singleton(const Singleton&) {cout << "calling copy constructor\n";}
    Singleton& operator= (const Singleton&);
  private:
    static Singleton* pinstance;
};

Singleton* Singleton::pinstance = 0;// initialize pointer

Singleton* Singleton::Instance ()
{
  if (pinstance == 0) // is it the first call?
  {
    pinstance = new Singleton; // create sole instance
  }
  return pinstance; // address of sole instance
}
Singleton::Singleton()
{
  //... perform necessary instance initializations
  cout << "Calling Protected Constructor" << endl;
}

int main()
{
    Singleton *p1 = Singleton::Instance();
    cout << "printing p1 --->" << p1 << endl;
    p1->printMessage();

    Singleton *p2 = p1->Instance();
    cout << "printing p2 --->"<< p2 << endl;
    p2->printMessage();

    Singleton *p3(p2);
    cout << "printing p3 --->" << p3 << endl;
    p3->printMessage();


    Singleton & ref = * Singleton::Instance();

    return 0;
}