设计模式：singleton模式

目的：限制类的实例个数只能是一个

例子：

#define AGT_DECLARE_SINGLETON(ClassName) 
public: 
    static ClassName *Instance();   
private:    
    static ClassName *m_pInstance; 
	
#define AGT_DEFINE_SINGLETON(ClassName)    
ClassName *ClassName::m_pInstance = NULL; 
ClassName *ClassName::Instance() 
{   
    if (NULL == m_pInstance) 
    {   
        m_pInstance = new ClassName; 
    }   
    return  m_pInstance;    
}   

class Manager
{
private:
	Manager() {} 
	
public:
	void show()
	{
		cout << "Success" << endl;
	}

public:	
	AGT_DECLARE_SINGLETON(Manager) //单例模式声明
};

AGT_DEFINE_SINGLETON(Manager); //函数实现

int main() 
{
	Manager* manager = Manager::Instance();
	manager->show();
	
	Manager* manager1 = Manager::Instance();
	Manager* manager2 = Manager::Instance();
	if(manager1 == manager2)
	{
		cout << "manager1 = manager2" << endl;
	}
	else
	{
		cout << "manager1 != manager2" << endl;
	}
	
	return 0;
}