c++ 单例

class Singleton
{
public:
static Singleton* Instance();
void print(void)
{
std::cout << "Hello World!" << std::endl;
}
protected:
Singleton();
private:
static Singleton* _instance;
};

Singleton::Singleton()
{

}
Singleton* Singleton::_instance = NULL;
Singleton* Singleton::Instance()
{
if(_instance == NULL)
{
_instance = new Singleton;
}
return _instance;
}
#define SINGLETON Singleton::Instance()

class Single
{
private:
Single(void);

public:
static Single instance;    
static Single &Instance(void)
{
//    if(instance == NULL)
//    {
//    instance = new Single;
//    }
return instance;
}
void print(void)
{
std::cout << "Hello World!" << std::endl;
}

~Single(void)
{
//    delete instance;
}

 

};

Single Single::instance ;
Single::Single()
{

}
#define SINGLE Single::Instance()
int main()
{
SINGLE.print();
SINGLETON->print();
return 0;
}