Convert a byte array to a class containing a byte array in C#

Question

I've got a C# function that converts a byte array to a class, given it's type:

IntPtr buffer = Marshal.AllocHGlobal(rawsize);
Marshal.Copy(data, 0, buffer, rawsize);
object result = Marshal.PtrToStructure(buffer, type);
Marshal.FreeHGlobal(buffer);

I use sequential structs:

[StructLayout(LayoutKind.Sequential)]
public new class PacketFormat : Packet.PacketFormat { }

This worked fine, until I tried to convert to a struct/class containing a byte array.

[StructLayout(LayoutKind.Sequential)]
public new class PacketFormat : Packet.PacketFormat
{
  public byte header;
  public byte[] data = new byte[256];
}

Marshal.SizeOf(type) returns 16, which is too low (should be 257) and causes Marshal.PtrToStructure to fail with the following error:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

I'm guessing that using a fixed array would be a solution, but can it also be done without having to resort to unsafe code?

Answer 1

You need to use a fixed size byte array.

[StructLayout(LayoutKind.Sequential)]
public unsafe struct PacketFormat
{
  public byte header;
  public fixed byte data[256];
}

Answer 2

No need for unsafe code:

[StructLayout(LayoutKind.Sequential)]
public struct PacketFormat
{
  public byte header;
  [MarshalAs(UnmanagedType.ByValArray, SizeConst = 256)] public byte[] data;
}