using System;

using System.Runtime.InteropServices;

​

 //The Struct needs to be annotated as "Explicit Layout", like this:

 [System.Runtime.InteropServices.StructLayout(LayoutKind.Explicit)]

 struct IpAddress

 {

   //The "FieldOffset:" means that this Integer starts 

   //a offset 0, in bytes, (with sizeof(int) = 4 bytes length): 

   [System.Runtime.InteropServices.FieldOffset(0)]

   public int intAddress;

​

   //Offset 0, (length sizeof(byte) = 1 byte)...   

   [System.Runtime.InteropServices.FieldOffset(0)]

   public byte Byte1;

​

   //Offset 1, (length sizeof(byte) = 1 byte)...     

   [System.Runtime.InteropServices.FieldOffset(1)]

   public byte Byte2;

​

   //Offset 2, (length sizeof(byte) = 1 byte)...   

   [System.Runtime.InteropServices.FieldOffset(2)]

   public byte Byte3;

   //Offset 3, (length sizeof(byte) = 1 byte)...    

   [System.Runtime.InteropServices.FieldOffset(3)]

   public byte Byte4;     

   public IpAddress(int address) {

         //All elements have to be initialized. it is a good idea to initialize the 

         //ones not being explicitly set first.

         Byte1 = Byte2 = Byte3 = Byte4 = 0;

​

         //Now, when we init the Int, the Bytes will change too.

         //If we had done this backwards, it would zero out the intAddress. 

         intAddress = address;

   }

     //Now we can use the explicit layout to access the 

     //bytes separately, without doing any conversion

     public override string ToString() {

         return (new System.Text.StringBuilder()).Append(Byte1).Append('.')

                 .Append(Byte2).Append('.')

                 .Append(Byte3).Append('.')

                 .Append(Byte4).ToString();

     }

 }

​

 //Now let's see if we can fit a whole URL into a long

​

 //Let's define a short enum to hold protocols

 enum Protocol : short {http,https,ftp,sftp,tcp};

​

 //The Service Struct will hold the Address, the Port and the Protocol

 [System.Runtime.InteropServices.StructLayout(LayoutKind.Explicit)]

 struct Service

 { 

   [System.Runtime.InteropServices.FieldOffset(0)]

   public IpAddress Address;

   [System.Runtime.InteropServices.FieldOffset(4)]

   public ushort Port;

   [System.Runtime.InteropServices.FieldOffset(6)]

   public Protocol AppProtocol;

   [System.Runtime.InteropServices.FieldOffset(0)]

   public long Payload;    

   public Service(IpAddress addr, ushort port, Protocol prot) {

         Payload = 0;      //Fields not set by the constructor must be init first

         Address = addr;

         Port  = port;

         AppProtocol = prot;         

   }

   public Service(long val) {

       //Defaults:

       Address = new IpAddress(0);

       Port = 80;  

       AppProtocol = Protocol.http;

       //Setting the argument

       Payload = val;

   }

   public Service Copy() {

         return new Service(Payload);

   }

    public override string ToString() {

         return AppProtocol + "//" + Address + ":" + Port + "/";

    }

 }

​

​

public class MainClass { 

​

    public static void Main()

    {

     var ip = new IpAddress((new Random()).Next());

     Console.Out.WriteLine( "Size (bytes): " + Marshal.SizeOf(ip) + 

                            ". Value:\t\t" + ip.intAddress + "\t=\t" + ip);

     var s1 = new Service(ip,8080,Protocol.https);

     var s2 = new Service(s1.Payload);  

     s2.Address.Byte1 = 100;

     s2.AppProtocol = Protocol.ftp;

     Console.Out.WriteLine("Size (bytes): " + Marshal.SizeOf(s1) + 

                           ". Value: " + s1.Payload + "\t=\t" + s1);

     Console.Out.WriteLine("Size (bytes): " + Marshal.SizeOf(s2) + 

                           ". Value: " + s2.Payload + "\t=\t" + s2);

    }   

}