Home » c# » How to convert a structure to a byte array in C#?

How to convert a structure to a byte array in C#?

Posted by: admin November 29, 2017 Leave a comment

Questions:

How do I convert a structure to a byte array in C#?

I have defined a structure like this:

public struct CIFSPacket
{
    public uint protocolIdentifier; //The value must be "0xFF+'SMB'".
    public byte command;

    public byte errorClass;
    public byte reserved;
    public ushort error;

    public byte flags;

    //Here there are 14 bytes of data which is used differently among different dialects.
    //I do want the flags2. However, so I'll try parsing them.
    public ushort flags2;

    public ushort treeId;
    public ushort processId;
    public ushort userId;
    public ushort multiplexId;

    //Trans request
    public byte wordCount;//Count of parameter words defining the data portion of the packet.
    //From here it might be undefined...

    public int parametersStartIndex;

    public ushort byteCount; //Buffer length
    public int bufferStartIndex;

    public string Buffer;
}

In my main method, I create an instance of it and assign values to it:

CIFSPacket packet = new CIFSPacket();
packet.protocolIdentifier = 0xff;
packet.command = (byte)CommandTypes.SMB_COM_NEGOTIATE;
packet.errorClass = 0xff;
packet.error = 0;
packet.flags = 0x00;
packet.flags2 = 0x0001;
packet.multiplexId = 22;
packet.wordCount = 0;
packet.byteCount = 119;

packet.Buffer = "NT LM 0.12";

Now I want to send this Packet by socket. For that, I need to convert the structure to a byte array. How can I do it?

My full code is as follows.

static void Main(string[] args)
{

  Socket MyPing = new Socket(AddressFamily.InterNetwork,
  SocketType.Stream , ProtocolType.Unspecified ) ;


  MyPing.Connect("172.24.18.240", 139);

    //Fake an IP Address so I can send with SendTo
    IPAddress IP = new IPAddress(new byte[] { 172,24,18,240 });
    IPEndPoint IPEP = new IPEndPoint(IP, 139);

    //Local IP for Receiving
    IPEndPoint Local = new IPEndPoint(IPAddress.Any, 0);
    EndPoint EP = (EndPoint)Local;

    CIFSPacket packet = new CIFSPacket();
    packet.protocolIdentifier = 0xff;
    packet.command = (byte)CommandTypes.SMB_COM_NEGOTIATE;
    packet.errorClass = 0xff;
    packet.error = 0;
    packet.flags = 0x00;
    packet.flags2 = 0x0001;
    packet.multiplexId = 22;
    packet.wordCount = 0;
    packet.byteCount = 119;

    packet.Buffer = "NT LM 0.12";

    MyPing.SendTo(It takes byte array as parameter);
}

What would a code snippet be?

Answers:

This is fairly easy, using marshalling.

Top of file

using System.Runtime.InteropServices

Function

byte[] getBytes(CIFSPacket str) {
    int size = Marshal.SizeOf(str);
    byte[] arr = new byte[size];

    IntPtr ptr = Marshal.AllocHGlobal(size);
    Marshal.StructureToPtr(str, ptr, true);
    Marshal.Copy(ptr, arr, 0, size);
    Marshal.FreeHGlobal(ptr);
    return arr;
}

And to convert it back:

CIFSPacket fromBytes(byte[] arr) {
    CIFSPacket str = new CIFSPacket();

    int size = Marshal.SizeOf(str);
    IntPtr ptr = Marshal.AllocHGlobal(size);

    Marshal.Copy(arr, 0, ptr, size);

    str = (CIFSPacket)Marshal.PtrToStructure(ptr, str.GetType());
    Marshal.FreeHGlobal(ptr);

    return str;
}

In your structure, you will need to put this before a string

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
public string Buffer;

And make sure SizeConst is as big as your biggest possible string.

And you should probably read this:
http://msdn.microsoft.com/en-us/library/4ca6d5z7.aspx

Questions:
Answers:

Have a look at these methods:

byte [] StructureToByteArray(object obj)
{
    int len = Marshal.SizeOf(obj);

    byte [] arr = new byte[len];

    IntPtr ptr = Marshal.AllocHGlobal(len);

    Marshal.StructureToPtr(obj, ptr, true);

    Marshal.Copy(ptr, arr, 0, len);

    Marshal.FreeHGlobal(ptr);

    return arr;
}

void ByteArrayToStructure(byte [] bytearray, ref object obj)
{
    int len = Marshal.SizeOf(obj);

    IntPtr i = Marshal.AllocHGlobal(len);

    Marshal.Copy(bytearray,0, i,len);

    obj = Marshal.PtrToStructure(i, obj.GetType());

    Marshal.FreeHGlobal(i);
}

This is a shameless copy of another thread which I found upon Googling!

Update : For more details, check the source

Questions:
Answers:

If you really want it to be FAST, you can do it using unsafe code with CopyMemory. CopyMemory is about 5x faster (e.g. 800MB of data takes 3s to copy via marshalling, while only taking .6s to copy via CopyMemory). This method does limit you to using only data which is actually stored in the struct blob itself, e.g. numbers, or fixed length byte arrays.

    [DllImport("kernel32.dll", EntryPoint = "CopyMemory", SetLastError = false)]
    private static unsafe extern void CopyMemory(void *dest, void *src, int count);

    private static unsafe byte[] Serialize(TestStruct[] index)
    {
        var buffer = new byte[Marshal.SizeOf(typeof(TestStruct)) * index.Length];
        fixed (void* d = &buffer[0])
        {
            fixed (void* s = &index[0])
            {
                CopyMemory(d, s, buffer.Length);
            }
        }

        return buffer;
    }

Questions:
Answers:

Variant of the code of Vicent with one less memory allocation:

public static byte[] GetBytes<T>(T str)
{
    int size = Marshal.SizeOf(str);

    byte[] arr = new byte[size];

    GCHandle h = default(GCHandle);

    try
    {
        h = GCHandle.Alloc(arr, GCHandleType.Pinned);

        Marshal.StructureToPtr<T>(str, h.AddrOfPinnedObject(), false);
    }
    finally
    {
        if (h.IsAllocated)
        {
            h.Free();
        }
    }

    return arr;
}

public static T FromBytes<T>(byte[] arr) where T : struct
{
    T str = default(T);

    GCHandle h = default(GCHandle);

    try
    {
        h = GCHandle.Alloc(arr, GCHandleType.Pinned);

        str = Marshal.PtrToStructure<T>(h.AddrOfPinnedObject());

    }
    finally
    {
        if (h.IsAllocated)
        {
            h.Free();
        }
    }

    return str;
}

I use GCHandle to “pin” the memory and then I use directly its address with h.AddrOfPinnedObject().

Questions:
Answers:

As the main answer is using CIFSPacket type, which is not (or no longer) available in C#, I wrote correct methods:

    static byte[] getBytes(object str)
    {
        int size = Marshal.SizeOf(str);
        byte[] arr = new byte[size];
        IntPtr ptr = Marshal.AllocHGlobal(size);

        Marshal.StructureToPtr(str, ptr, true);
        Marshal.Copy(ptr, arr, 0, size);
        Marshal.FreeHGlobal(ptr);

        return arr;
    }

    static T fromBytes<T>(byte[] arr)
    {
        T str = default(T);

        int size = Marshal.SizeOf(str);
        IntPtr ptr = Marshal.AllocHGlobal(size);

        Marshal.Copy(arr, 0, ptr, size);

        str = (T)Marshal.PtrToStructure(ptr, str.GetType());
        Marshal.FreeHGlobal(ptr);

        return str;
    }

Tested, they work.

Questions:
Answers:

You can use Marshal (StructureToPtr, ptrToStructure), and Marshal.copy but this is plataform dependent.


Serialization includes Functions to Custom Serialization.

public virtual void GetObjectData(SerializationInfo info, StreamingContext context)
Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext) 

SerializationInfo include functions to serialize each member.


BinaryWriter and BinaryReader also contains methods to Save / Load to Byte Array (Stream).

Note that you can create a MemoryStream from a Byte Array or a Byte Array from a MemoryStream.

You can create a method Save and a method New on your structure:

   Save(Bw as BinaryWriter)
   New (Br as BinaryReader)

Then you select members to Save / Load to Stream -> Byte Array.

Questions:
Answers:

This can be done very straightforwardly.

Define your struct explicitly with [StructLayout(LayoutKind.Explicit)]

int size = list.GetLength(0);
IntPtr addr = Marshal.AllocHGlobal(size * sizeof(DataStruct));
DataStruct *ptrBuffer = (DataStruct*)addr;
foreach (DataStruct ds in list)
{
    *ptrBuffer = ds;
    ptrBuffer += 1;
}

This code can only be written in an unsafe context. You have to free addr when you’re done with it.

Marshal.FreeHGlobal(addr);

Questions:
Answers:

I would take a look at the BinaryReader and BinaryWriter classes. I recently had to serialize data to a byte array (and back) and only found these classes after I’d basically rewritten them myself.

http://msdn.microsoft.com/en-us/library/system.io.binarywriter.aspx

There is a good example on that page too.

Questions:
Answers:

Looks like a predefined (C level) structure for some external library. Marshal is your friend. Check:

http://geekswithblogs.net/taylorrich/archive/2006/08/21/88665.aspx

for a starter how to deal with this. Note that you can – with attributes – define things like byte layout and string handling. VERY nice approach, actually.

Neither BinaryFormatter Nor MemoryStream are done for that.

Questions:
Answers:

@Abdel Olakara answer donese not work in .net 3.5, should be modified as below:

    public static void ByteArrayToStructure<T>(byte[] bytearray, ref T obj)
    {
        int len = Marshal.SizeOf(obj);
        IntPtr i = Marshal.AllocHGlobal(len);
        Marshal.Copy(bytearray, 0, i, len);
        obj = (T)Marshal.PtrToStructure(i, typeof(T));
        Marshal.FreeHGlobal(i);
    }

Questions:
Answers:
        Header header = new Header();
        Byte[] headerBytes = new Byte[Marshal.SizeOf(header)];
        Marshal.Copy((IntPtr)(&header), headerBytes, 0, headerBytes.Length);

This should do the trick quickly, right?

Questions:
Answers:

This example here is only applicable to pure blittable types, e.g., types that can be memcpy’d directly in C.

Example – well known 64-bit struct

[StructLayout(LayoutKind.Sequential)]  
public struct Voxel
{
    public ushort m_id;
    public byte m_red, m_green, m_blue, m_alpha, m_matid, m_custom;
}

Defined exactly like this, the struct will be automatically packed as 64-bit.

Now we can create volume of voxels:

Voxel[,,] voxels = new Voxel[16,16,16];

And save them all to a byte array:

int size = voxels.Length * 8; // Well known size: 64 bits
byte[] saved = new byte[size];
GCHandle h = GCHandle.Alloc(voxels, GCHandleType.Pinned);
Marshal.Copy(h.AddrOfPinnedObject(), saved, 0, size);
h.Free();
// now feel free to save 'saved' to a File / memory stream.

However, since the OP wants to know how to convert the struct itself, our Voxel struct can have following method ToBytes:

byte[] bytes = new byte[8]; // Well known size: 64 bits
GCHandle h = GCHandle.Alloc(this, GCHandleType.Pinned);
Marshal.Copy(hh.AddrOfPinnedObject(), bytes, 0, 8);
h.Free();

Questions:
Answers:

I’ve come up with a different approach that could convert any struct without the hassle of fixing length, however the resulting byte array would have a little bit more overhead.

Here is a sample struct:

[StructLayout(LayoutKind.Sequential)]
public class HelloWorld
{
    public MyEnum enumvalue;
    public string reqtimestamp;
    public string resptimestamp;
    public string message;
    public byte[] rawresp;
}

As you can see, all those structures would require adding the fixed length attributes. Which could often ended up taking up more space than required. Note that the LayoutKind.Sequential is required, as we want reflection to always gives us the same order when pulling for FieldInfo. My inspiration is from TLV Type-Length-Value. Let’s have a look at the code:

public static byte[] StructToByteArray<T>(T obj)
{
    using (MemoryStream ms = new MemoryStream())
    {
        FieldInfo[] infos = typeof(T).GetFields(BindingFlags.Public | BindingFlags.Instance);
        foreach (FieldInfo info in infos)
        {
            BinaryFormatter bf = new BinaryFormatter();
            using (MemoryStream inms = new MemoryStream()) {

                bf.Serialize(inms, info.GetValue(obj));
                byte[] ba = inms.ToArray();
                // for length
                ms.Write(BitConverter.GetBytes(ba.Length), 0, sizeof(int));

                // for value
                ms.Write(ba, 0, ba.Length);
            }
        }

        return ms.ToArray();
    }
}

The above function simply uses the BinaryFormatter to serialize the unknown size raw object, and I simply keep track of the size as well and store it inside the output MemoryStream too.

public static void ByteArrayToStruct<T>(byte[] data, out T output)
{
    output = (T) Activator.CreateInstance(typeof(T), null);
    using (MemoryStream ms = new MemoryStream(data))
    {
        byte[] ba = null;
        FieldInfo[] infos = typeof(T).GetFields(BindingFlags.Public | BindingFlags.Instance);
        foreach (FieldInfo info in infos)
        {
            // for length
            ba = new byte[sizeof(int)];
            ms.Read(ba, 0, sizeof(int));

            // for value
            int sz = BitConverter.ToInt32(ba, 0);
            ba = new byte[sz];
            ms.Read(ba, 0, sz);

            BinaryFormatter bf = new BinaryFormatter();
            using (MemoryStream inms = new MemoryStream(ba))
            {
                info.SetValue(output, bf.Deserialize(inms));
            }
        }
    }
}

When we want to convert it back to its original struct we simply read the length back and directly dump it back into the BinaryFormatter which in turn dump it back into the struct.

These 2 functions are generic and should work with any struct, I’ve tested the above code in my C# project where I have a server and a client, connected and communicate via NamedPipeStream and I forward my struct as byte array from one and to another and converted it back.

I believe my approach might be better, since it doesn’t fix length on the struct itself and the only overhead is just an int for every fields you have in your struct. There are also some tiny bit overhead inside the byte array generated by BinaryFormatter, but other than that, is not much.