C# P/Invoke structure problem

Question

I am trying to write a C# P/Invoke wrapper for a C API (a native Win dll), and generally this is working fine. The only exception is a specific method which takes a struct a

Answer 1

Looks to me like the problem is that you're passing a reference by reference. Since MSTrackData is a class (i.e. reference type), passing it by reference is like passing a pointer-to-pointer.

Change your managed prototype to:

public static extern bool EncodeMagstripe(IntPtr hDC,
                    MSTrackData pTrack1,
                    MSTrackData pTrack2,
                    MSTrackData pTrack3,
                    MSTrackData reserved);

See the MSDN article about passing structures.