Re: Who can explain this code for me?about virtual function

From:

"Alexander Nickolov" <agnickolov@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 25 Oct 2007 11:46:39 -0700

Message-ID:

<uLTmFdzFIHA.4956@TK2MSFTNGP06.phx.gbl>

The class has a pure virtual method thus it cannot be
instantiated. Hence the __declspec(novtable) optimization.

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"IOCPer" <kuibing@gmail.com> wrote in message
news:1193299090.466208.52350@e34g2000pro.googlegroups.com...

///////////////////////////////////////////////
// CIOMessageMap.h
class __declspec(novtable) CIOMessageMap
{
public:
virtual bool ProcessIOMessage(IOType clientIO, ClientContext*
pContext, DWORD dwSize) = 0;
};

#define BEGIN_IO_MSG_MAP() \
public: \
bool ProcessIOMessage(IOType clientIO, ClientContext* pContext, DWORD
dwSize = 0) \
{ \
bool bRet = false;

#define IO_MESSAGE_HANDLER(msg, func) \
if (msg == clientIO) \
bRet = func(pContext, dwSize);

#define END_IO_MSG_MAP() \
return bRet; \
}

Why class CIOMessageMap should be declared by declspec(novtable)?
The macros implements the member function of CIOMessageMap --
ProcessIOMessage();But in other places of project,there no any
inheritances of CIOMessageMap.
Who can tell me the advantages about this coding style?
There are will best in detail.