Serial ports

[Russ]

Ok, I followed the example of passing a managed class, which is
basically a structure, to an unmanaged call in the VC++ .Net Step by
Step book (page 522).

Now I tried this with GetCommState cause I need to talk to this serial
device.

Here's the class:

///////////////////////////////////////////////
#pragma once

using namespace System::Runtime ::InteropServic es;

[StructLayoutAtt ribute(LayoutKi nd::Sequential)]
__gc class PDCB
{
public:
System::UInt32 DCBlength;
System::UInt32 BaudRate;
System::UInt32 fBitFields;
System::UInt16 wReserved;
System::UInt16 XonLim;
System::UInt16 XoffLim;
System::Byte ByteSize;
System::Byte Parity;
System::Byte StopBits;
System::Char XonChar;
System::Char XoffChar;
System::Char ErrorChar;
System::Char EofChar;
System::Char EvtChar;
System::UInt16 wReserved1;
};
///////////////////////////////////////////////

Just like the example in the book, but with using a DCB structure.

When I call GetCommState:
MyKernel::GetCo mmState( m_MyFileStream->get_Handle() , p_dcb );

p_dcb is empty, filled with zeros.

BUT, when I change make the PDCB class unmanaged (__nogc) and remove
the layout call directly above, THEN IT WORKS.

So, why does it work with __nogc and NOT WORK with __gc????
The example in the book uses __gc and it works.
Guess I'm not understanding something basic here.