cocos3 深入理解单例模式

#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;
}