QueryInterface IID_IDispatch

STDMETHODIMP CMathFactory::QueryInterface(REFIID riid,void ** ppv)
{
	*ppv=NULL;
	if(riid==IID_IUnknown||riid==IID_IClassFactory)//这儿不改变也可以！
	//if(riid==IID_IUnknown||riid==IID_IClassFactory || riid == IID_IDispatch)//改变
	{
		*ppv=static_cast<IClassFactory *>(this);
		reinterpret_cast<IUnknown*>(*ppv)->AddRef();
		return S_OK;
	}
	else
		return (*ppv=0),E_NOINTERFACE;
}

STDMETHODIMP CMath::QueryInterface(REFIID riid, void **ppv)
{//	这里这是实现dynamic_cast的功能，但由于dynamic_cast与编译器相关。
	if(riid == IID_ISimpleMath)
		*ppv = static_cast<ISimpleMath *>(this);
	else if(riid == IID_IAdvancedMath)
		*ppv = static_cast<IAdvancedMath *>(this);
	else if(riid == IID_IUnknown)
		*ppv = static_cast<ISimpleMath *>(this);
	else if(riid == IID_IDispatch)
		 //*ppv = static_cast<ISimpleMath *>(this);//方一
		 *ppv = static_cast<IAdvancedMath *>(this);//方二，都可以！
	else {
		*ppv = 0;
		return E_NOINTERFACE;
	}

	reinterpret_cast<IUnknown *>(*ppv)->AddRef();	//这里要这样是因为引用计数是针对组件的
	return S_OK;
}