最简单单例模式

#include <iostream>
using namespace std;
class Single
{
 private:
  Single(){}
  static Single* instance;
 public:
  static Single* getInstance() {
   if(instance==NULL){
    instance=new Single;
   }
   return instance;
  }
  void f(){
   cout<<"f()"<<endl;
  }
};
Single* Single::instance=NULL;

int main()
{
 Single *s1=Single::getInstance();
 Single *s2=Single::getInstance();
 s1->f();
 s2->f();
 cout<<(int)(s1)<<endl;
 cout<<(int)(s2)<<endl;

 return 0;
}