C++ Singleton单例模式

Version6：

#include <iostream>
using namespace std;

template<class T>
class Singleton
{
private:
public:
	static T& GetInstance()//唯一对外开放的接口
	{
		static T instance;//C++11已经加锁，可以通过汇编看出来guard
		return instance;
	}
protected://保护类型，因为子类继承的时候要调用父类构造函数，写成public肯定不行，写成private子类就无法访问，就需要写friend class Manager了，写成protected，子类可以访问到Singleton构造函数，就不需要友元了
	Singleton(){ cout << "Singeton" << endl; }
	virtual ~Singleton(){ cout << "~Singeton" << endl; }
	Singleton &operator=(const Singleton&){}
};


class Manager :public Singleton < Manager >
{
public:
	friend class Singleton<Manager>;//Singleton作为子类的友员，Singleton就可以在GetInstance中访问子类的protected的方法了。
	void SendTask(){}
	void Meeting(){}
protected:
	Manager(){ cout << "Manager" << endl; }
	~Manager(){ cout << "~Manager" << endl; }
	Manager&operator=(const Manager &){}

};

int main()
{
	Manager& pInstance = Manager::GetInstance();
	pInstance.SendTask();
	pInstance.Meeting();
}