Union in c# with StructLayout

c#, structlayout, union

Solution

Byte[] is a reference type field, which you cannot overlay with a value type field. You need a fixed size buffer and you need to compile it with `/unsafe`. Like this:

[StructLayout(LayoutKind.Explicit, Size = 255)]
public unsafe struct RecBuffer
{

    [FieldOffset(0)]
    public long header;

    [FieldOffset(0)]
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.I1, SizeConst = 255)]
    public fixed Byte buffer[255];
};

Problem

I have multiple structs that all starts with a header struct. Like this ``` public struct BaseProtocol { public Header header; public Footer footer; }; ``` The header is ``` public struct Header { public Byte start; public Byte group; public Byte dest; public Byte source; public Byte code; public Byte status; }; ``` The problem now is that I need to union them with a Byte[]. I tried it with this ``` [StructLayout( LayoutKind.Explicit, Size=255 )] public struct RecBuffer { [FieldOffset( 0 )] public Header header; [FieldOffset( 0 )] [MarshalAs( UnmanagedType.ByValArray, ArraySubType = UnmanagedType.I1, SizeConst = 255 )] public Byte[] buffer; }; ``` When I fill the buffer with data I can't get the data from the header. How can I make c# do the same as I can do with union in c++?

Original source