Crash on calling ResetDC with devmode copied to byte array from marshalled structure

I am getting a System.AccessViolationException on a call to ResetDC when passing my Devmode. I am doing the following..

// create and marshall the devmode to a byte array.

DEVMODE myDevmode = new DEVMODE {dmSize = (short) Marshal.SizeOf(typeof (DEVMODE))};

myDevmode.dmFields = DM.Orientation;
myDevmode.dmOrientation = DMORIENT_LANDSCAPE;

IntPtr ptDM = Marshal.AllocHGlobal(myDevmode开发者_运维百科.dmSize);
Marshal.StructureToPtr(myDevmode, ptDM, false);

byte[] byteDM = new byte[myDevmode.dmSize];
Marshal.Copy(ptDM, byteDM, 0, myDevmode.dmSize);

I then call across a com interface (existing architecture not possible to change) the method:

SetDevMode(ref byteDM[0], myDevmode.dmSize)

on the other side of the com interface and back in .net code the other side the following is run:

    public void SetDevMode(ref byte pDevMode, int nDevModeSize)
    {
        _pageSetupDevMode = new byte[nDevModeSize];

        unsafe
        {
            fixed (byte* p = &pDevMode)
            {
                Marshal.Copy((IntPtr)p, _pageSetupDevMode, 0, nDevModeSize);
            }
        }
    }

and at a later point a call to ResetDC is made:

Win32.ResetDC(_hRefDc, ref _pageSetupDevMode[0]);

at which point I get the exception.

An unhandled exception of type 'System.AccessViolationException' occurred Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

This occurrs in gdi32.dll

Any ideas?

---

As mentioned in the comment above, this was not an issue with the memory handling but rather the result of passing an all but empty devmode into ResetDC - I had seen this done in a sample online but it seems to 'upset' gdi while printing.

I am now getting a valid devmode from the printer as the basis of the above code and this works fine. Apologies.