How to convert an IPv4 address into a integer in C#?

Question

I was going to attempt to write this function myself but I thought that someone on SO might know the answer :)

I'm basically looking for a function that will convert a standard IPv4 address into an Integer. Bonus points available for a function that will do the opposite.

Solution should be in C#.net.

Answer 1

// IPv4
int intAddress = BitConverter.ToInt32(IPAddress.Parse(address).GetAddressBytes(), 0);
string ipAddress = new IPAddress(BitConverter.GetBytes(intAddress)).ToString();

EDIT: As noted in other answers, when running this snippet on a little endian machine, it'll give out the bytes in the reverse order as defined by the standard. However, the question asks for a mapping between an integer and an IP address, not converting to the standard integer format. To do so, you have to consider the endian-ness of the machine you're running on.

Answer 2

32-bit unsigned integers are IPv4 addresses. Meanwhile, the IPAddress.Address property, while deprecated, is an Int64 that returns the unsigned 32-bit value of the IPv4 address (the catch is, it's in network byte order, so you need to swap it around).

For example, my local google.com is at 64.233.187.99. That's equivalent to:

64*2^24 + 233*2^16 + 187*2^8 + 99
= 1089059683

And indeed, http://1089059683/ works as expected (at least in Windows, tested with IE, Firefox and Chrome; doesn't work on iPhone though).

Here's a test program to show both conversions, including the network/host byte swapping:

using System;
using System.Net;

class App
{
    static long ToInt(string addr)
    {
        // careful of sign extension: convert to uint first;
        // unsigned NetworkToHostOrder ought to be provided.
        return (long) (uint) IPAddress.NetworkToHostOrder(
             (int) IPAddress.Parse(addr).Address);
    }

    static string ToAddr(long address)
    {
        return IPAddress.Parse(address.ToString()).ToString();
        // This also works:
        // return new IPAddress((uint) IPAddress.HostToNetworkOrder(
        //    (int) address)).ToString();
    }

    static void Main()
    {
        Console.WriteLine(ToInt("64.233.187.99"));
        Console.WriteLine(ToAddr(1089059683));
    }
}

Answer 3

If you were interested in the function not just the answer here is how it is done:

int ipToInt(int first, int second, 
    int third, int fourth)
{
    return Convert.ToInt32((first * Math.Pow(256, 3))
        + (second * Math.Pow(256, 2)) + (third * 256) + fourth);
}

with first through fourth being the segments of the IPv4 address.

Answer 4

@Barry Kelly and @Andrew Hare, actually, I don't think multiplying is the most clear way to do this (alltough correct).

An Int32 "formatted" IP address can be seen as the following structure

[StructLayout(LayoutKind.Sequential, Pack = 1)] 
struct IPv4Address
{
   public Byte A;
   public Byte B;
   public Byte C;
   public Byte D;
} 
// to actually cast it from or to an int32 I think you 
// need to reverse the fields due to little endian

So to convert the ip address 64.233.187.99 you could do:

(64  = 0x40) << 24 == 0x40000000
(233 = 0xE9) << 16 == 0x00E90000
(187 = 0xBB) << 8  == 0x0000BB00
(99  = 0x63)       == 0x00000063
                      ---------- =|
                      0x40E9BB63

so you could add them up using + or you could binairy or them together. Resulting in 0x40E9BB63 which is 1089059683. (In my opinion looking in hex it's much easier to see the bytes)

So you could write the function as:

int ipToInt(int first, int second, 
    int third, int fourth)
{
    return (first << 24) | (second << 16) | (third << 8) | (fourth);
}

Answer 5

My question was closed, I have no idea why . The accepted answer here is not the same as what I need.

This gives me the correct integer value for an IP..

public double IPAddressToNumber(string IPaddress)
    {
        int i;
        string [] arrDec;
        double num = 0;
        if (IPaddress == "")
        {
            return 0;
        }
        else
        {
            arrDec = IPaddress.Split('.');
            for(i = arrDec.Length - 1; i >= 0 ; i = i -1)
                {
                    num += ((int.Parse(arrDec[i])%256) * Math.Pow(256 ,(3 - i )));
                }
            return num;
        }
    }

Answer 6

here's a solution that I worked out today (should've googled first!):

    private static string IpToDecimal2(string ipAddress)
    {
        // need a shift counter
        int shift = 3;

        // loop through the octets and compute the decimal version
        var octets = ipAddress.Split('.').Select(p => long.Parse(p));
        return octets.Aggregate(0L, (total, octet) => (total + (octet << (shift-- * 8)))).ToString();
    }

i'm using LINQ, lambda and some of the extensions on generics, so while it produces the same result it uses some of the new language features and you can do it in three lines of code.

i have the explanation on my blog if you're interested.

cheers, -jc

Answer 7

Try this ones:

private int IpToInt32(string ipAddress)
{
   return BitConverter.ToInt32(IPAddress.Parse(ipAddress).GetAddressBytes().Reverse().ToArray(), 0);
}

private string Int32ToIp(int ipAddress)
{
   return new IPAddress(BitConverter.GetBytes(ipAddress).Reverse().ToArray()).ToString();
}

Answer 8

I think this is wrong: "65536" ==> 0.0.255.255" Should be: "65535" ==> 0.0.255.255" or "65536" ==> 0.1.0.0"