Singleton单件模式

class Singleton
{
public:
       static Singleton* Instance() ;
protected:
       Singleton() {}
private:
       static Singleton *_instance ;
       Singleton(const Singleton&) ;
       Singleton& operator=(const Singleton&) ;
} ;
 
Singleton* Singleton::_instance = NULL ;
 
Singleton* Singleton::Instance()
{
       (_instance == NULL) ? _instance = new Singleton() : 0 ; //lazy initialization
       return _instance ;
}

#define PATTERN_SINGLETON_DECLARE(classname)
private:										\
	classname();								\
public:											\
	static classname * instance();				\
	virtual ~classname();	

#define PATTERN_SINGLETON_IMPLEMENT(classname)	\
classname * classname::instance()		\
{												\
	static classname * _instance = NULL;		\
	if( NULL == _instance)						\
	{											\
		_instance = new classname;				\
	}											\
	return _instance;							\
}												

class Singleton
{
       PATTERN_SINGLETON_DECLARE(Singleton);
private:
       Singleton(const Singleton&) ;
       Singleton& operator=(const Singleton&) ;
} ;
 
PATTERN_SINGLETON_IMPLEMENT(Singleton);