Check Format of DNS or IP

Question

For the below coding, how to check the Host format, e.g. The Host is the DNS or IP, if the user inputted www.yahoo.com or 203.20.20.203, so it is correct, but if the user inputted aaa or 123, so it will prompt to input a correct DNS or IP format. Please give me reply asap. Thanks! string sHost = txtHost.Text; sHost.Trim(); if (sHost.Length == 0 ) { MessageBox.Show('Please enter Host!','Warning',MessageBoxButtons.OK,MessageBoxIcon.Information); txtHost.Focus(); return; } fm Softair

ms44cn · Answer

got it

thed0ct0r · Answer

You should use a regularexpression that checks the input string format. You can find a lot of regularexpression on the web

Ben · Answer

Softair, Try this. It's not a very effecient way to check the IP or DNS, but until someone else posts a bbetter answer... //At the top of your code add: //using System.Net; string sHost = txtHost.Text.Trim(); //check if string is an IP address try { //make sure at the top of your code you use //using System.Net; IPAddress validIp = IPAddress.Parse(sHost); } //if it's not an IP address, try it as a dns catch { bool validPrefix = false; bool validDns = false; //add as many prefixes as you want string[] dnsPrefixes = new string[]{ "http:\www.", "www.", "ftp." }; //again, add as many suffixes as needed string[] dnsSuffixes = new string[]{ ".com", ".net", ".gov", ".org", ".mil", ".edu", ".co", ".uk" }; foreach(string prefix in dnsPrefixes) { //the prefix needs to be at the beginning of the address if(sHost.ToLower().IndexOf(prefix) == 0) { validPrefix = true; } } //if we have a valid prefix, check the suffix if(validPrefix == true) { foreach(string suffix in dnsSuffixes) { //the suffix can't be at the beginning if(sHost.ToLower().IndexOf(suffix) >= 3) { validDns = true; } } } //if it isn't a dns, then display your message to enter a host if(validDns != true) { MessageBox.Show("Please enter Host!","Warning",MessageBoxButtons.OK,MessageBoxIcon.Information); txtHost.Focus(); } } I hope this will help you temporarily ;)

Check Format of DNS or IP

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