Return string from catch System.Net.Sockets.SocketException

Question

I have a button that should convert a list of hostnames to the matching IP addresses in a textbox. How can I just return string "No host is known" for the hostname that is really not known to the textbox?

I use try-catch block in which I catch System.Net.Sockets.SocketException. But as far that I know, catch block cannot return any string value. So, I usually catch the exception by output a messagebox. But this time, I just want it to display a string in the specified textbox. This is the code that I've tried:-

private void btnConvertHosttoIP_Click(object sender, Eventrgs e)
{
    try
    {
        string ips = null;
        List<string> ipList = new List<string>();
        string[] hostList = Regex.Split(txtHost.Text, "\r\n");
        foreach (var h in hostList)
        {
            // Check DNS
            if (h.Contains(".xxxx.com"))
            {
                hostName = h;
            }
            else
            {
                string code = txtHost.Text.Substring(0, 3);
                if (code == "ABC" || code == "CDE")
                    hostName = h + ".ap.xxx.com";
                else
                    hostName = "Unknown domain name";
            }

            IPHostEntry host = Dns.GetHostEntry(hostName);
            IPAddress[] ipaddr = host.AddressList;

            // Loop through the IP Address array and add the IP address to Listbox
            foreach (IPAddress addr in ipaddr)
            {
                if (addr.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
                {
                    ipList.Add(addr.ToString());
                }
            }
        }
        foreach (var ip in ipList)
        {
            ips += ip + Environment.NewLine;
        }
        txtIP.Text = ips;
    }
    catch (System.Net.Sockets.SocketException ex)
    {
        MessageBox.Show(ex.Message);
    }
}

I want the unknown host to be displayed in the textbox only not as an exception. Is it possible or any other suggestions?

Answer 1

You can modify your code as below.

try
{
    string ips = null;
    List<string> ipList = new List<string>();
    string[] hostList = Regex.Split(txtHost.Text, "\r\n");
    foreach (var h in hostList)
    {
        // Check DNS
        if (h.Contains(".xxxx.com"))
        {
            hostName = h;
        }
        else
        {
            string code = txtHost.Text.Substring(0, 3);
            if (code == "ABC" || code == "CDE")
                hostName = h + ".ap.xxx.com";
            else
                hostName = "Unknown domain name";
        }
        try
       {
        IPHostEntry host = Dns.GetHostEntry(hostName);
        IPAddress[] ipaddr = host.AddressList;

        // Loop through the IP Address array and add the IP address to Listbox
        foreach (IPAddress addr in ipaddr)
        {
            if (addr.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
            {
                ipList.Add(addr.ToString());
            }
        }
      } 
      catch (System.Net.Sockets.SocketException ex)
     {
         ipList.Add("Invalid Host");
     }
    }
    foreach (var ip in ipList)
    {
        ips += ip + Environment.NewLine;
    }
    txtIP.Text = ips;
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}