Marshalling struct with embedded pointer from C# to unmanaged driver

Question

I\'m trying to interface C# (.NET Compact Framework 3.5) with a Windows CE 6 R2 stream driver using P/Invoked DeviceIoControl() calls . For one of the IOCTL codes, the driv

Answer 1

You might have to specify the size of the byte[] (replace 64 with the actual size)

[StructLayout(LayoutKind.Sequential, Pack=1)]
public struct IoctlWriteRegsIn
{    
   public uint Address; 
   [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)] 
   public byte[] Buffer; 
   public uint Size;
}

Then you should be able to set the size like this:

IoctlWriteRegsIn io_struct = new IoctlWriteRegsIn();
io_struct.Address = 5;
io_struct.Buffer = new byte[1] { 0xBE };
// size of buffer, not struct
io_struct.Size = 1;//Marshal.SizeOf(io_struct); 

I would change the P/Invoke call to this:

[DllImport("coredll.dll", CharSet = CharSet.Unicode, SetLastError = true)]
static extern bool DeviceIoControl(IntPtr hDevice,  
   UInt32 dwIoControlCode,
   ref IoctlWriteRegsIn lpInBuffer, 
   UInt32 nInBufferSize,
   IntPtr lpOutBuffer,
   UInt32 nOutBufferSize,
   ref UInt32 lpBytesReturned,
   IntPtr lpOverlapped);

and call it using this:

uint num_bytes = (uint)Marshal.SizeOf(writeInBuffer);
bool writeSuccess = DeviceIoControl(driverHandle, IoctlTwlWriteRegs, ref writeInBuffer, num_bytes, IntPtr.Zero, 0, ref numBytesReturned, IntPtr.Zero);

Answer 2

When marshaling a struct which has an inline pointer, you need to define the value as an IntPtr and not an array

[StructLayout(LayoutKind.Sequential)]
public struct IoctlWriteRegsIn
{
    public uint Address;
    public IntPtr Buffer;
    public uint Size;
}

Answer 3

Give it a shot by replacing the byte[] array with an IntPtr..