Question

The following is a bit of C++ that is verified working:

typedef struct
{
  PVOID  buffer;
  UINT32 length;
} DATA_BUFFER;

typedef struct 
{
  DATA_BUFFER TxBuf [1];
  DATA_BUFFER RxBuf [1];
} JVM_COMM_BUFFER;

UINT32 SendAndRecv(
  IN    JHI_HANDLE        handle,
  IN    CHAR*             AppId,
  INOUT JVM_COMM_BUFFER* pComm
);

The following is my attempt to port that to C#:

    [StructLayout(LayoutKind.Sequential)]
    public struct DATA_BUFFER
    {
        public byte[] buffer;
        public uint length;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct JVM_COMM_BUFFER
    {
        public DATA_BUFFER TxBuf;
        public DATA_BUFFER RxBuf;
    }

    [DllImport("jhi.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Auto)]
    public static extern UInt32 SendAndRecv(IntPtr handle, string AppId, ref JVM_COMM_BUFFER pComm);

There is no exception thrown in the C# from marshalling, but the results are not the same for the C++ and C# versions. Any idea on what I’m missing?

Answer 1

The issue is the difference between just allocating memory and allocating a pinned object. Once I switched it to a pinned object, then the signature without any IntPtrs except the buffer field worked just fine.