An application sends a CB_GETLBTEXT message to retrieve a string from the list of a combo box.
CB_GETLBTEXT wParam = (WPARAM) index; // item index lParam = (LPARAM) (LPCSTR) lpszBuffer; // address of buffer
The return value is the length of the string, in bytes, excluding the terminating null character. If the index parameter does not specify a valid index, the return value is CB_ERR.
If you create the combo box with an owner-drawn style but without the CBS_HASSTRINGS style, the buffer pointed to by the lpszBuffer parameter of the message receives the 32-bit value associated with the item (the item data).