Singleton design pattern

singleton.cpp

#include<iostream>
using namespace std;

class Singleton
{
  int x;
  Singleton(int v):x(v){ }
  Singleton(Singleton const&);
  Singleton& operator=(Singleton const&);
  public:
  static Singleton& getInstance();
  int getXValue();
  void setXValue(int v);
};

Singleton& Singleton::getInstance()
{
  static Singleton instance(12);
  return instance;
}
int Singleton::getXValue()
{
  return x;
}
void Singleton::setXValue(int v)
{
  this->x = v;
}

int main()
{
  Singleton& s = Singleton::getInstance();
  cout<<Singleton::getInstance().getXValue()<<endl;
  cout<<s.getXValue()<<endl;
  cout<<&s<<endl;
  Singleton::getInstance().setXValue(100);
  cout<<Singleton::getInstance().getXValue()<<endl;
  cout<<s.getXValue()<<endl;
  cout<<&Singleton::getInstance()<<endl;
  return 0;
}