An application sends an LB_GETSEL message to retrieve the selection state of an item.
LB_GETSEL wParam = (WPARAM) index; // item index lParam = 0; // not used; must be zero
Windows 95: The wParam parameter is limited to 16-bit values. This means list boxes cannot contain more than 32,767 items. Although the number of items is restricted, the total size in bytes of the items in a listbox is limited only by available memory.
If an item is selected, the return value is greater than zero; otherwise, it is zero. If an error occurs, the return value is LB_ERR.