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.
CB_ADDSTRING, CB_GETITEMDATA, CB_INSERTSTRING
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