The DDX_CBString function manages the transfer of CString data between the edit control of a combo box control in a dialog box, form view, or control view object and a CString data member of the dialog box, form view, or control view object.
When DDX_CBString is called, value is set to the current combo box selection. If no item is selected, value is set to a string of zero length.
If the combo box is a drop-down list box, the value exchanged is limited to 255 characters.
For more information about DDX, see Dialog Data Exchange and Validation.