An application sends a LB_DELETESTRING message to delete a string in a list box.
wParam
Specifies the zero-based index of the string to deleted.
lParam
This parameter is not used.
The return value is a count of the strings remaining in the list. The return value is LB_ERR if the wParam parameter specifies an index greater then the number of items in the list.
If the combo box was created with an owner-draw style but without the LBS_HASSTRINGS style, a WM_DELETEITEM message is sent to the owner of the list box so that the application can free any additional data associated with the item.
WM_DELETEITEM