Design Pattern

单例模式

1. 将构造函数、拷贝构造函数和赋值符号函数私有化
2. 在类中定义一个静态的指向本类型的指针变量
3. 定义一个返回值为类指针的静态成员函数

   class Singleton {
   public:
       static Singleton * getInstance(){
           if(nullptr == _pInstance)
               { _pInstance = new Singleton(); }
           return _pInstance;
       } 
       static void Delete(){
           if(_pInstance)
               delete _pInstance;
       }
   private:
       Singleton() {}
       Singleton(Singleton &other){}
       void operator=(const Singleton &) {}
   private:
       Static Singleton * _pInstance;
   };
   Singleton * Singleton::_pInstance = nullptr;

这样不是自动释放

class Singleton
{
private:
	static Singleton* instance;
private:
	Singleton() { };
	~Singleton() { };
	Singleton(const Singleton&);
	Singleton& operator=(const Singleton&);
private:
	class Deletor {
	public:
		~Deletor() {
			if(Singleton::instance != NULL)
				delete Singleton::instance;
		}
	};
	static Deletor deletor;
public:
	static Singleton* getInstance() {
		if(instance == NULL) {
			instance = new Singleton();
		}
		return instance;
	}
};

// init static member
Singleton* Singleton::instance = NULL;
Singleton::Deletor Singleton::deletor;

Reference: C++ 单例模式