LB_SETITEMDATA message

Sets a value associated with the specified item in a list box.

wParam

Specifies the zero-based index of the item. If this value is -1, the lParam value applies to all items in the list box.

Windows 95/Windows 98/Windows Millennium Edition (Windows Me): 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.

lParam

Specifies the value to be associated with the item.

If an error occurs, the return value is LB_ERR.

If the item is in an owner-drawn list box created without the LBS_HASSTRINGS style, this message replaces the value contained in the lParam parameter of the LB_ADDSTRING or LB_INSERTSTRING message that added the item to the list box.

Reference

LB_ADDSTRING

LB_GETITEMDATA

LB_INSERTSTRING