复制datatable，把类型变为字符串

 DataTable dtcp = tblDeliveryInfo.Clone();
            foreach (DataColumn item in dtcp.Columns)
            {
                item.DataType = typeof(string);
            }
            foreach (DataRow item in tblDeliveryInfo.Rows)
            {
                DataRow dr = dtcp.NewRow();

                for (int i = 0; i < item.ItemArray.Length; i++)
               {
                   dr[i] = item.ItemArray[i];
                }

                dtcp.Rows.Add(dr);
            }