CSDNS

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Environment: VS7, C#, .NET

This program is an example of using the DNS class to resolve host names to IP addresses and, where available, resolves host names from IP addresses. The methods for doing this are similar to the sockets functions gethostbyname and gethostbyaddr. Not all IP addresses resolve into host names; it depends on the DNS server, which may or may not have a reverse mapping defined. There also are asynchronous methods for doing the same functions. There even is a method, Dns.Resolve, that determines whether an IP address or host name is used and calls the appropriate method.

//-------------------------------------------------------
private void HostNameButtonClick(object sender,
                                 System.EventArgs e)
{
  m_status.Text = "Trying....";
  m_status.Update();
try
{
  IPHostEntry hostInfo = Dns.GetHostByName(m_host_name.Text);
  m_ip_address.Text    = hostInfo.AddressList[0].ToString();
  m_status.Text        = "ok";
}
catch (Exception excpt)
{
  m_status.Text = excpt.Message;
  m_ip_address.Text = "";
}
MessageBeep(1000);
}
//-------------------------------------------------------
private void IPAddressButtonClick(object sender,
                                  System.EventArgs e)
{
  IPAddress ipaddr = IPAddress.Parse(m_ip_address.Text);
  m_status.Text    = "Trying....";
  m_status.Update();
try
{
  IPHostEntry hostInfo = Dns.GetHostByAddress (ipaddr);
  m_host_name.Text     = hostInfo.HostName;
  m_status.Text        = "ok";
}
catch (Exception excpt)
{
  m_status.Text    = excpt.Message;
  m_host_name.Text = "";
}
  MessageBeep(1000);
}
//------------------------------------------------------
private void ResolveButtonClick(object sender,
                                System.EventArgs e)
{
  m_status.Text = "Trying....";
  m_status.Update();
try
{
  IPHostEntry hostInfo = Dns.Resolve(m_resolve_text.Text);
  m_ip_address.Text    = hostInfo.AddressList[0].ToString();
  m_host_name.Text     = hostInfo.HostName;
  m_status.Text        = "ok";
}
catch (Exception excpt)
{
  m_status.Text = excpt.Message;
  m_ip_address.Text = "";
}
  MessageBeep(1000);
}
//------------------------------------------------------

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