How to pass RECT in COM

Question

I need to get a RECT from COM to C# in 64 bits, so I defined a simple method in IDL as:

[id(23), helpstring("method GetRect")] HRESULT GetRect([out,retval] RECT* pRect);

and implemented in C++ as

STDMETHODIMP CSpot::GetRect(RECT* pRect)
{
CRect rec = get_position(); 
*pRect = rec;
return S_OK;
}

I called in C# as:

tagRECT rec = pSpot.GetRect();

Most time is OK, but sometimes I get 0xC0000005: Access violation writing location 0x0000000000000000.

in line:

*pRect = rec;

What could cause this exception?

Answer 1

Not sure if this is your problem, but when using RECT from COM methods, I need to 'define' the RECT object as following:

[StructLayout(LayoutKind.Sequential, Pack = 0)]
public struct RECT
{
    public int left;
    public int top;
    public int right;
    public int bottom;
}