An application sends an LB_GETCOUNT message to retrieve the number of items in a list box.
LB_GETCOUNT wParam = 0; // not used; must be zero lParam = 0; // not used; must be zero
This message has no parameters.
The return value is the number of items in the list box, or LB_ERR if an error occurs.
The returned count is one greater than the index value of the last item (the index is zero-based).