REFERENCE GUIDE

SefWindowsHookIParamPoints to the message structure.Return valueThe return value specifies the outcome of the function. It is nonzero if thehook function processes the message. Otherwise, it is zero.WH_SYSMSGFILTERWindows calls the WH_SYSMSGFILTER filter function whenever a dialogbox, message box, or menu has retrieved a message and before it hasprocessed that message. The filter allows an application to process ormodify messages for any application in the system.The filter function must use the Pascal calling convention and must bedeclared FAR. The filter function must have the following form:Filter Function DWORD FAR PASCAL FilterFunc(nCode, wParam, IParam )int nCode;WORD wParam;DWORD IParam;FilterFunc is a placeholder for the library-supplied function name. Theactual name must be exported by including it in an EXPORTS statementin the library'S module-definition file.Parameters nCode Specifies the type of message being processed. It must beone of the following values:wParamIParamValueMSGF _DIALOGBOXMSGF _MENUMeaningProcessing messages inside theDialogBox function.Processing keyboard and mousemessages in menu.MSGF _MESSAGEBOX Processing messages inside theMessageBox function.If the nCode parameter is less than zero, the filter functionmust pass the message to DefHookProc without furtherprocessing and return the value returned by DefHookProc.Specifies a NULL value.Points to the message structure.Return valueThe return value specifies the outcome of the function. It is nonzero if thehook function processes the message. Otherwise, it is zero.544 Software development kit