Question

In Mono you can pass a delegate from C# to a C++ function which takes in the delegate as a function pointer. Can this be done in C# on Windows for example where you can compile a native C++ unmanaged library, link it against a C# project and get a C++ function to invoke a C# function via a function pointer which C# passed to it as a delegate?

Answer 1

Define a delegate in .NET, and then pass that to your unmanaged code. The CLR will expose the delegate as a function pointer which you can call from your unmanaged code.

The interop layer does not know how to handle references in C++. So You need to expose the object as a pointer, not a reference. Additionally, .NET doesn’t know what a C++
object is (it’s not the same as System.Object). That will need to be passed
as an IntPtr, and I don’t think there is much you can do with it in .NET.

C++ callbacks:

typedef void (*CBFUNC1)(unsigned int, const char*, object&);
typedef object* (*CBFUNC2)(object*, struct _mystruct* );

C# signatures for the delegates would be

delegate void CbFunc1(uint param1, [MarshalAs(UnmanagedType.LPStr)] string
param2, IntPtr param3);
delegate IntPtr CbFunc2(IntPtr param1, ref _mystruct param2);