单例模式

#include <iostream>
#include <mutex>
using namespace std;
//内嵌类用来析构static单例
//内嵌类可以访问私有函数，所以可以被嵌套类中私有析构函数
//测试
#define Lazyman2
#ifdef Lazyman1
/**********懒汉模式**********/
//线程不安全,双判断锁，外层判断的作用是节省每次调用都上锁的开销
/*懒汉1:静态成员指针实现*/
class singleton{
private:
	singleton(){};
	~singleton(){};
	singleton(const singleton& a);
	singleton& operator=(const singleton& a);
	class Garbage{
	public:
	    ~Garbage(){
			if (singleton::sig != nullptr){
				cout << "完成析构" << endl;
				delete singleton::sig;
			}
		}
	};
public:
	static singleton* sig;
	static mutex mut;
	static Garbage garbage;
	static singleton* getinstance(){
		if (sig == nullptr){
			mut.lock();
			if (sig == nullptr)
				sig = new singleton();
			mut.unlock();
		}
		return sig;
	}
};
std::mutex singleton::mut;
singleton* singleton::sig = nullptr;
singleton::Garbage singleton::garbage;
#endif // Lazyman

#ifdef Lazyman2
/*懒汉2:静态成员变量*/
class singleton{
private:
	singleton(){};
	~singleton(){};
	singleton(const singleton& a);
	singleton& operator=(const singleton& a);
public:
	static singleton& getinstance(){
		static singleton sig;
		return sig;
	}
	这里可以使用shared_ptr解决释放问题
	static shared_ptr<singleton>& getinstance() {/*加不加引用都可以，加引用就是返回指针管理器的引用
		static shared_ptr<singleton> p(new singleton);
		return p;
	}
	//可以返回指针
	//static singleton* getinstance(){
	//	static singleton sig;
	//	return &sig;
	//}
};
#endif
/**********饿汉模式**********/
#ifdef Hungryman1
/*饿汉1:静态成员指针实现*/
class singleton{
private:
	singleton(){};
	~singleton(){};
	singleton(const singleton& a);
	singleton& operator= (singleton& a);
	class Garbage{
	public:
		~Garbage(){
			if (singleton::sig != nullptr){
				cout<<"完成析构"<<endl;
				delete singleton::sig;
			}		
		}
	};
public:
	static singleton* sig;
	static Garbage garbage;
	static singleton* getinstance(){
		return sig;
	}
};
singleton::Garbage singleton::garbage;
singleton* singleton::sig = new singleton();
#endif

#ifdef Hungryman2
/*饿汉2:静态成员变量*/
class singleton{
private:
	singleton(){};
	~singleton(){};
	singleton(const singleton& a);
	singleton& operator= (singleton& a);
public:
	static singleton sig;
	static singleton& getinstance(){
		return sig;
	}
	//可以返回指针
	//static singleton* getinstance(){
	//	return &sig;
	//}
};
singleton singleton::sig;
#endif