#include <iostream>#include <stdio.h>#include <stdlib.h>#include <string.h>using namespace std;class Singleton  {public:    int i;    static Singleton* GetInstance();    virtual void Show() {}protected: //必须为保护，如果是私有属性，子类无法访问父类的构造函数    Singleton() {}private:    static Singleton *singleton; //唯一实例的指针};Singleton* Singleton::singleton = NULL;Singleton* Singleton::GetInstance(){    if(singleton == NULL)    {        if(singleton == NULL)            singleton = new Singleton();    }    return singleton;}int main(){    Singleton* sin=Singleton::GetInstance();    sin->i=200;    Singleton* sin2=Singleton::GetInstance();    cout<<sin2->i<<endl;    return 0;}