Question

Is it possible to marshal a C-style struct containing bit-fields to a C# struct, or would you have to marshal it to a basic type and then do bit-masks?

E.g. I would like to marshal from a C style structure like this:

struct rgb16 {
    unsigned int R : 4;
    unsigned int G : 5;
    unsigned int B : 4;
}

And marshal it onto something like this:

[StructLayout(LayoutKind.Sequential)]
public struct Rgb16 {
    public byte R;
    public byte G;
    public byte B;
}

Answer 1

There are no bit-fields in C#. So I’d go with properties that encapsulate the bit fiddling:

[StructLayout(LayoutKind.Sequential)]
public struct Rgb16 {
    private readonly UInt16 raw;
    public byte R{get{return (byte)((raw>>0)&0x1F);}}
    public byte G{get{return (byte)((raw>>5)&0x3F);}}
    public byte B{get{return (byte)((raw>>11)&0x1F);}}

    public Rgb16(byte r, byte g, byte b)
    {
      Contract.Requires(r<0x20);
      Contract.Requires(g<0x40);
      Contract.Requires(b<0x20);
      raw=r|g<<5|b<<11;
    }
}

I’ve avoided adding setters, because I like immutable structs, but in principle you can add them too.