To get all computed column names of a datawindow

Pb 10.5

I create a datawindow with this sql
select cust_code from customer

Then In datawindow I make another copy of cust_code and give the colunm_name say 'cust_name'

IN constructor event II am doing this and my intention is to know all column names including computed columns of datawindow
      FOR I = 1 TO Integer(dw_master.Describe('Datawindow.Column.Count'))  
         ls_colname  = dw_master.Describe('#' + Trim(String(i)) + '.Name')
         messagebox('', ls_colname)
      next
the          messagebox('', ls_colname) never display "cust_name"

Is there anyway to find computed column names of datawindow