I just purchased a book on sockets and I noticed something I've never seen befor. The simple client app is a doc/view VC++ 6.0 using CAsynSocket.
Anyways I created a class called CClientSocket which inherits from CAsyncSocket.
but on top of this class the books says to add the Doc file like so:

class CNoBlkCliDoc;

class CClientSocket : public CAsynSocket{
public:
CClientSocket( CNoBlkCliDoc *pDoc );

CNoBlkCliDoc *m_pDoc;
...
...

};

I've never seen the use of the class that way before( class CNoBlkCliDoc ), tried looking it up but couldnt find info on it. Can anyone explain why I would need to do that?
Meaning use the class CNoBlkCliDoc.
I put the following code that used the CNoBlkCliDoc class.

Any info?
Thanks