An application sends an LB_SETANCHORINDEX message to set the anchor item—that is, the item from which a multiple selection starts. A multiple selection spans all items from the anchor item to the caret item.
LB_SETANCHORINDEX
wParam = (WPARAM) index; // index to set as anchor
lParam = 0; // not used; must be zero
Windows 95 and Windows 98: 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 list box is limited only by available memory.
If the message succeeds, the return value is zero.
If the message fails, the return value is LB_ERR.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
List Boxes Overview, List Box Messages, LB_GETANCHORINDEX