Sets a pointer to the list-box item
int SetItemDataPtr( int nIndex, void* dwItemData );
Specifies the zero-based index of the item in the list box.
Specifies the pointer to be associated with the item.
-1 if an error occurs.
Sets the 32-bit value associated with the specified item in a list box to be the specified pointer (void*). This pointer remains valid for the life of the list box, even though the item's relative position within the list box might change as items are added or removed. Hence, the item's index within the box can change, but the pointer remains reliable.