How to convert an IPv4 address into a integer in C

Question

I'm 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#.

Answer 1

I have encountered some problems with the described solutions, when facing IP Adresses with a very large value. The result would be, that the byte[0] * 16777216 thingy would overflow and become a negative int value. what fixed it for me, is the a simple type casting operation.

public static long ConvertIPToLong(string ipAddress)
{
    System.Net.IPAddress ip;

    if (System.Net.IPAddress.TryParse(ipAddress, out ip))
    {
        byte[] bytes = ip.GetAddressBytes();

        return (long)
            (
            16777216 * (long)bytes[0] +
            65536 * (long)bytes[1] +
            256 * (long)bytes[2] +
            (long)bytes[3]
            )
            ;
    }
    else
        return 0;
}

Answer 2

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 3

var ipAddress = "10.101.5.56";

var longAddress = long.Parse(string.Join("", ipAddress.Split('.').Select(x => x.PadLeft(3, '0'))));

Console.WriteLine(longAddress);

Output: 10101005056

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

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 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