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;
}