dataset写入xml

private void Button5_Click(object sender, System.EventArgs e)
  {
   SqlConnection myconn = new SqlConnection("server=.;uid=sa;pwd=;database=test");
   myconn.Open();
   SqlDataAdapter myad = new SqlDataAdapter("select * from xuesheng",myconn);
   DataSet myds = new DataSet();
   myad.Fill(myds);
   myds.WriteXml("c://a.xml");
   myad.Dispose();
   myconn.Close();
  
  }