I have been playing with some interop over the last copule of days and
have a small problem. I am trying to use DeviceIOControl to talk to a
custom driver. I have successfull called CreateFile and have used
DeviceIOControl to initialise the device. The problem I have is when i
try to send data.

I have a struct

typedef struct POLL_STRUCT {
    UINT    nSize;            // size of struct
    UINT    nPollSize;        // number of bytes to send
    UINT    nMaxSize;        // max chars expected
    BYTE    zBuffer[MAX_RX_SIZE];    // (poll->driver,
driver->poll+response)
}    TPOLL_STRUCT;

MAX_RX_SIZE is always 2048 bytes.

I have declared the c# struct as:

[StructLayout(LayoutKind.Sequential)]
struct POLL_STRUCT {
    public uint nSize;
    public uint nPollSize;
    public uint nMaxSize;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2048)]
    byte [] zBuffer;
    };

Now I thought that MarshalAs attribute would create the zbuffer
instance, but when i try to reference it it is null?

Now when i try and marshal the TPOLL_STRUCT;

lpPollBuffer =
Marshal.AllocHGlobal(Marshal.SizeOf(typeof(TPOLL_STRUCT)));

I seems to work fine, however, if i try to copy data to the array,

Array.Copy(fooArray,abyPollBuffer,fooArray.Length); <-- Exception

The Exception is an argument null exception. This makes sense, as i
already know that zBuffer is null. But AllocHGlobal has obviously
allocated the 2048 bytes on the heap, where is it in the managed code?

If I create and instance of the buffer like so;

abyPollBuffer.zbuffer = new byte[2048];

does this data get marshaled to the unmanaged heap?

I can for the life of me find and way to view the actual memory in the
c# debugger either, so I cant confirm.

Furthermore, If I was to make a struct like so:
[StructLayout(LayoutKind.Sequential)]
struct FOO{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2048)]
    byte [] data;
    uint uiMoreData;
    };

Is uiMoreData 2048 bytes after of data[0] ?? How in VS2005 do I view
the addresses of the data?

Sorry if these questions sound stupid. I was all excited about moving
to c# (from c++) now I am getting increasingly frustrated. I am sure
that once I adjust all will be good. I do miss my pointers though ;).