An application sends a CB_SETITEMDATA message to set the 32-bit value associated with the specified item in a combo box.
CB_SETITEMDATA
wParam = (WPARAM) index; // item index
lParam = (LPARAM) (DWORD) dwData; // item data
If an error occurs, the return value is CB_ERR.
If the specified item is in an owner-drawn combo box created without the CBS_HASSTRINGS style, this message replaces the 32-bit value in the lParam parameter of the CB_ADDSTRING or CB_INSERTSTRING message that added the item to the combo box.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Combo Boxes Overview, Combo Box Messages, CB_ADDSTRING, CB_GETITEMDATA, CB_INSERTSTRING