How to modify VB.NET structure passed to C++ DLL

I need to pass a structure from VB.NET program to C++ program in order to modify the members of the structure. 

I had the DLL set up and working in my VB.Net program before the need to modify the structure but I needed to.

Here is how I define the DLL in VB.NET

<DllImport("ConvertRaw.dll", CallingConvention:=CallingConvention.Cdecl)>
Public Shared Function OpenRawFile(<MarshalAs(UnmanagedType.LPStr)> x As String, ByRef CurrentStamp As RawDataHeader) As Integer
End Function

Public Structure RawDataHeader
   Public syncpattern As Integer
   Public runnumber As As Integer
   Public muxpitch As Integer
   Public ThisChannel() As Integer
  End Structure

typedef struct {
   int      syncpattern;                        
   int      run;                            
   int      datastream;
   std::vector<int> channels;                 
  }RawDataHeader;

MYDLL_API int OpenRawFile(const char* fileName, RawDataHeader &stamp)
{

   long offset;
   long size;

   pfile.open(fileName, ios::binary);
   //long myDataStampSize = GetDataStampSize();
   if (!pfile.is_open())
   {
      std::cout << "ERROR";
   }

   pfile.seekg(0, pfile.end);
   length = pfile.tellg();
   pfile.seekg(0, pfile.beg);
   offset = length - stampSize;

      // Start from the end and read
   pfile.seekg(0, pfile.end);
   pfile.seekg(-4, pfile.end);
   pfile.read((char*)&numChannels, sizeof(numChannels));

   stamp.channels.resize(numChannels);

   pfile.seekg(offset, pfile.beg);
   pfile.read((char*)&stamp.syncpattern, sizeof(int));
   pfile.read((char*)&stamp.run, sizeof(int));
   pfile.read((char*)&stamp.datastream, sizeof(int));

   for (int i = 0; i < numChannels; i++)
   {
      pfile.read((char*)&stamp.channels[i], sizeof(int));
   }

    pfile.close();
   return 0;
}