I did this once a few years ago, back in the days of Managed C++. We had some business logic in an umanaged DLL that we wanted to incorporate into a wizard-style GUI written in C#. To do this, I created a Managed C++ assembly to site between the managed GUI app and the unmanaged DLL and used System::Runtime::InteropServices::Marshal within that assembly to convert values from managed types (System::Int32) to unmanaged types (int) and vice versa.

While Managed C++ appears to be deprecated, the same principal might apply to C++/CLI.

I did this once a few years ago, back in the days of Managed C++. We had some business logic in an umanaged DLL that we wanted to incorporate into a wizard-style GUI written in C#. To do this, I created a Managed C++ assembly to sit between the managed GUI app and the unmanaged DLL and used System::Runtime::InteropServices::Marshal within that assembly to convert values from managed types (System::Int32) to unmanaged types (int) and vice versa.

While Managed C++ appears to be deprecated, the same principal might apply to C++/CLI.