Declares that the class defines a message map. Each CCmdTarget-derived class in your program must provide a message map to handle messages.
Use the DECLARE_MESSAGE_MAP macro at the end of your class declaration. Then, in the .cpp file that defines the member functions for the class, use the BEGIN_MESSAGE_MAP macro, macro entries for each of your message-handler functions, and the END_MESSAGE_MAP macro.
If you declare any member after DECLARE_MESSAGE_MAP, you must specify a new access type (public, private, or protected) for them.
For more information on message maps and the DECLARE_MESSAGE_MAP macro, see Message Handling and Mapping Topics.