Marshal C++ "string" class in C# P/Invoke

Question

I have a function in a native DLL defined as follows:

#include <string>
void SetPath(string path);

I tried to put this in Microsoft's P/Invoke Interop Assistant, but it chokes on the "string" class (which I think is from MFC?).

I have tried marshaling it as a variety of different types (C# String, char[], byte[]) but every time I either get a NotSupportedException or a Native Assembly Exception (depending on what marshaling I tried).

As anyone ever done Native/Managed Interop where the native string class is used? Is there any way to Marshal this? Am I going to have to write my own Marshaler?

Answer 1

Looks like you're trying to use the C++ standard library string class. I doubt that will be easy to Marshal. Better to stick with a char * and Marshal as StringBuilder. That's what I usually do. You'll have to add a wrapper that generates the C++ string for you.

Answer 2

The PInvoke interop assistant only supports C not C++. Unfortunately the MFC String class (CString I believe?) is C++ and won't work through the assistant. Instead try using the following

void SetPath(__in const WCHAR* path);