An application sends an LB_GETANCHORINDEX message to retrieve the index of the anchor item¾that is, the item from which a multiple selection starts. A multiple selection spans all items from the anchor item to the caret item.
LB_GETANCHORINDEX wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
The return value is the index of the anchor item.