Remarks
This flag indicates the direction of a dialog data exchange (DDX) operation. The flag is nonzero if the CDataExchange object is being used to move data from the dialog controls to dialog-class data members after the user edits the controls. The flag is zero if the object is being used to initialize dialog controls from dialog-class data members.
The flag is also nonzero during dialog data validation (DDV).
For more information on writing your own DDX and DDV routines, see Technical Note 26. For an overview of DDX and DDV, see Dialog Data Exchange and Validation and Dialog Box Topics in Visual C++ Programmer's Guide.