Question

I want to be able to receive some binary data over TCP/IP which consists of a known structure.
I don’t want to inter-operate with C or C++, so solutions that work for this case didn’t help me.
Unfortunately the other side cannot change the protocol.
The problem should also arise when I would try to read a binary file with a given format.

I also checked BinaryFormatter and similar but they use their own format which is not acceptable for me.

Here is a sample set of structs. I’d like to be able to reconstruct nested arrays (of known length) of structs. With the current code I get an exception:

Could not load type ‘NestedStruct’ from assembly ‘…’ because it
contains an object field at offset 2 that is incorrectly aligned or
overlapped by a non-object field.

I want to be able to send/receive (or read/write) instances of struct MainStruct.

    [StructLayout(LayoutKind.Explicit, Pack = 1, Size = 244, CharSet = CharSet.Ansi)]
    public struct NestedStruct
    {

        [FieldOffset(0)]
        public Int16 someInt;

        [FieldOffset(2), MarshalAs(UnmanagedType.ByValArray, SizeConst = 242)]
        public Byte[] characterArray; // an array of fixed length 242

    }

    [StructLayout(LayoutKind.Explicit)]
    public struct OtherNestedStruct
    {
        [FieldOffset(0)]
        public Int16 someInt;
        [FieldOffset(2)]
        public Int16 someOtherInt;

    }


    [StructLayout(LayoutKind.Explicit)]
    public struct MainStruct
    {
        [FieldOffset(0)]
        public double someDouble;
        [FieldOffset(8)]
        public NestedStruct nestedContent;
        [FieldOffset(8 + 244)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 13 * 4)]
        public OtherNestedStruct[] arrayOfStruct; // fixed array length 13

    }

UPDATE:

Here is my latest version:

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public struct NestedStruct
    {

        public Int16 someInt;

        [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 242)]
        public Byte[] characterArray; // an array of fixed length 242

    }

    [StructLayout(LayoutKind.Sequential , Pack=1)]
    public struct OtherNestedStruct
    {
        public Int16 someInt;
        public Int16 someOtherInt;

    }


    [StructLayout(LayoutKind.Sequential, Pack=1)]
    public struct MainStruct
    {

        public double someDouble;

        public NestedStruct nestedContent;

        [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct,  SizeConst = 13)]
        public OtherNestedStruct[] arrayOfStruct; // fixed array length 13

    }

Answer 1

you must specify the ArraySubType

    [StructLayout(LayoutKind.Sequential, Pack = 1)]
    public struct NestedStruct
    {
        public Int16 someInt;
        [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 242)]
        public Byte[] characterArray; // an array of fixed length 242
    }

     [StructLayout(LayoutKind.Sequential, Pack = 1)]
     public struct OtherNestedStruct
     {
         public Int16 someInt;
         public Int16 someOtherInt;

     }


     [StructLayout(LayoutKind.Sequential, Pack = 1)]
     public struct MainStruct
     {
         public double someDouble;
         public NestedStruct nestedContent;
         [MarshalAs(UnmanagedType.ByValArray, SizeConst = 13 * 4)]
         public OtherNestedStruct[] arrayOfStruct; // fixed array length 13

    }  

    static void Main(string[] args)
    {
        var x = Marshal.SizeOf(typeof(MainStruct));
        //x == 460
    }