CODEWITHSUNDEEP
c#splitip-address
Botonomous
Botonomous

Reputation: 1764

Change last octet of IP returned by gethostentry

Was wondering if anyone could help me out here. I don't dont much with c# but its easy for what im trying to do.

I am making a small application that will take in the hostname on my network and then return the full ipaddress(ipv4) ....From there i have options to ping/vnc/telnet...etc.

My question lies here... I am using GetHostEntry to return the ip address. Then I want to store the IP into a variable, and change the last octet. I figured a simple sting.split('.') would be the answer, but I can't convert the IP to a string because the source is not a string. Any ideas?

Here is my Method to get the IP address, its just the basic GetHostEntry method: 

IPHostEntry host = Dns.GetHostEntry( hostname );

Console.WriteLine( "GetHostEntry({0}) returns: {1}", hostname, host );

// This will loop though the IPAddress system array and echo out
// the results to the console window

foreach ( IPAddress ip in host.AddressList )
{
    Console.WriteLine( "    {0}", ip );
}

Upvotes: 3

Views: 1563

Answers (3)

Metro Smurf
Metro Smurf

Reputation: 38335

Assuming there is only one network adapter:

// When an empty string is passed as the host name, 
// GetHostEntry method returns the IPv4 addresses of the local host
// alternatively, could use: Dns.GetHostEntry( Dns.GetHostName() )
IPHostEntry entries = Dns.GetHostEntry( string.Empty );
// find the local ipv4 address
IPAddress hostIp = entries.AddressList
                  .Single( x => x.AddressFamily == AddressFamily.InterNetwork );

Once you have the host IP, you can then use the IP bytes to create a new IP address by modifying any of the octets. In your case, you're wanting the last octect to be modified:

// grab the bytes from the host IP
var bytes = hostIp.GetAddressBytes();
// set the 4th octect (change 10 to whatever the 4th octect should be)
bytes[3] = 10;
// create a new IP address
var newIp = new IPAddress( bytes );

Of course, you can change any of the octets. The above example is only for the 4th octet. If you wanted the first octet, you'd use bytes[0] = 10.

Upvotes: 1

ladenedge
ladenedge

Reputation: 13419

Here's a rather brittle method that relies on the byte order of your machine and, obviously, the family of the provided address.

byte[] ipBytes = ip.GetAddressBytes();
while (ipBytes[0]++ < byte.MaxValue)
{
  var newIp = new IPAddress(ipBytes);
  Console.WriteLine("    {0}", ip);
}

Upvotes: 0

djdanlib
djdanlib

Reputation: 22496

You can convert it to a string by using the IPAddress object's ToString() method.

Have you considered just using the System.Net.IPAddress object?

Here is the document on its Parse method, which takes a string and attempts to convert it to an IPAddress object, so you could do whatever string magic you wanted to do: http://msdn.microsoft.com/en-us/library/system.net.ipaddress.parse.aspx

Or, if you want to know how to convert a string to a number, try the numeric data type's TryParse method. Perhaps Int32.TryParse would work.

Upvotes: 0

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