了解了通過模板來使用單件模式
*.h
template <typename T> class CEGUIEXPORT Singleton
{
protected:
    static T* ms_Singleton;

public:
    Singleton( void )
    {
        assert( !ms_Singleton );
        ms_Singleton = static_cast<T*>(this);//這個this是指的什么???不能理解,誰能幫我說明下么?謝謝
    }
   ~Singleton( void )
        {  assert( ms_Singleton );  ms_Singleton = 0;  }
    static T& getSingleton( void )
        {  assert( ms_Singleton );  return ( *ms_Singleton );  }
    static T* getSingletonPtr( void )
        {  return ( ms_Singleton );  }
};
使用如下
class MyClass :public Singleton<MyClass>
{
public:
    void run();
};
*.cpp

template MyClass* Singleton<MyClass>::ms_Singleton = NULL; ///注意,這里是Singleton構(gòu)造函數(shù).不是getSingleton方法
//好像也可以用    template<typename T> T* Singleton<T>::ms_Singleton = NULL;
//在使用它之前new一個對象
new MyClass();
MyClass::getSingleton().run();

在CEGUI中為什么不設(shè)計如下呢??????????????????????????????
emplate <class T> class  Singleton
{
protected:
    Singleton(){}
public:
    static T& Instance()
    {
        static T instance;
        return instance;
    }
};

// Concrete singleton class, derived from Singleton<T>
class ExampleSingleton: public Singleton<ExampleSingleton>
{
    // so that Singleton<ExampleSingleton> can access the 
    // protected constructor
    friend class Singleton<ExampleSingleton>;

protected:
        ExampleSingleton(){}
public:
    // This class's real functionalities
    void Write(){printf("Hello, World!");}
};

// use this singleton class
ExampleSingleton::Instance().Write();