SingleTon Pattern

#ifndef _SINGLETON_H_
#define _SINGLETON_H_

#include <iostream>
using namespace std;

class Singleton
{
 public:
    static Singleton* Instance();

 protected:
    Singleton();

 private:
    static Singleton* _instance;
}

#endif

#include "Singleton.h"

#include <iostream>
using namespace std;

Singleton* Singleton::_instance = 0;
Singleton::Singleton()
{
  cout<<"Singleton...."<<endl;
}

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

注：Singleton不可以被实例化，因此将其构造函数声明为protected或者直接声明为private。