An application sends an LB_GETCARETINDEX message to determine the index of the item that has the focus rectangle in a multiple-selection list box. The item may or may not be selected.
LB_GETCARETINDEX wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
The return value is the zero-based index of the list box item that has the focus rectangle. If the list box is a single-selection list box, the return value is the zero-based index of the item that is selected, if any.