LB_GETSEL
wParam = (WPARAM) index; /* item index */
lParam = 0L; /* not used, must be zero */
An application sends an LB_GETSEL message to retrieve the selection state of an item.
index
Value of wParam. Specifies the zero-based index of the item.
The return value is a positive number if an item is selected; otherwise, it is zero. The return value is LB_ERR if an error occurs.