I need to marshall a struct containing a union. The union part is not
being correctly passed. Any ideas on what I am missing or doing wrong?

Thanks for your help!
Johann

The win32 struct looks like this:

typedef struct {
 WAVEFORMATEX  Format;
 union {
   WORD  wValidBitsPerSample;
   WORD  wSamplesPerBlock;
   WORD  wReserved;
 } Samples;
 DWORD   dwChannelMask;
 GUID    SubFormat;
} WAVEFORMATEXTENSIBLE, *PWAVEFORMATEXTENSIBLE;

This is how I converted the struct to c#...

[StructLayout(LayoutKind.Sequential)] public struct WaveFormatEx
{
 public ushort wFormatTag;
 public ushort nChannels;
 public uint nSamplesPerSec;
 public uint nAvgBytesPerSec;
 public ushort nBlockAlign;
 public ushort wBitsPerSample;
 public ushort cbSize;
}

[StructLayout(LayoutKind.Explicit)] public struct Samples
{
 [FieldOffset(0)] public ushort wValidBitsPerSample;
 [FieldOffset(0)] public ushort wSamplesPerBlock;
 [FieldOffset(0)] public ushort wReserved;
}

[StructLayout(LayoutKind.Sequential)] public struct
WaveFormatExtensible
{
 public WaveFormatEx waveFormatEx;
 public Samples samples;
 public uint dwChannelMask;
 public Guid SubFormat;
}

WaveFormatExtensible fmt = new WaveFormatExtensible();

WaveFormatEx waveFormatEx = new WaveFormatEx();

waveFormatEx.wFormatTag = 0xFFFE;
waveFormatEx.nChannels = 2;
waveFormatEx.nSamplesPerSec = 44100;
waveFormatEx.nAvgBytesPerSec = 44100 * 4 * 2;
waveFormatEx.nBlockAlign = 8;
waveFormatEx.wBitsPerSample = 24;
waveFormatEx.cbSize = (ushort)
Marshal.SizeOf(typeof(WaveFormatExtensible));

fmt.waveFormatEx = waveFormatEx;

WaveNative.Samples samples = new WaveNative.Samples();

samples.wValidBitsPerSample = 24;  // These 3 members end up not being
passed correctly.
samples.wSamplesPerBlock = 24;
samples.wReserved = 24;

fmt.samples = samples;

fmt.dwChannelMask = 3;

fmt.SubFormat = new Guid("00000001-0000-0010-8000-00aa00389b71");