CB_GETITEMDATA
wParam = (WPARAM) index; /* item index */
lParam = 0; /* not used, must be zero */
An application sends a CB_GETITEMDATA message to a combo box to retrieve the application-supplied 32-bit value associated with the specified item in the combo box.
index
Value of wParam. Specifies the zero-based index of the item.
The return value is the 32-bit value associated with the item, or CB_ERR if an error occurs.
If the item is in an owner-draw combo box created without the CBS_HASSTRINGS style, the return value from this function is the 32-bit value contained in the lParam parameter of the CB_ADDSTRING or CB_INSERTSTRING message that added the item to the combo box. Otherwise, it is the value in the lParam parameter of a CB_SETITEMDATA message.
CB_SETITEMDATA