Parameters are incorrect after passing from C# to unmanaged dll

Question

Have been trying all day and searching various sources but can't find a solution. I am calling an imported unmanaged dll function from c#.

C++ class looks like:

class  MyModule
{
public:
    MYMODULEDLL_API int __cdecl Init(int);
...

Defined in C# like this:

 [DllImport("MyModule_x64.dll", EntryPoint = 
  "?Init@MyModule@@QEAAHH@Z", CallingConvention = CallingConvention.Cdecl)]
    public static extern int Init(int len);

And calling like this:

Init(configFileName.Length);

I can see in the debugger that the proper function in the dll is being called, but the passed parameter is corrupted showing a completely different value than what was passed. This is happening for string parameters as well. Is there anyway to troubleshoot the marshalling of parameters between managed and unmanaged code?

Answer 1

You can`t use C++ classes using DLLImport or PINVOKE, because it is suitable only for C style functions.

If you want to use C++ class in C#, you need to go with C++/CLI. You can create an unmanaged dll in native C++ and then create a simple C++/CLI wrapper which calls methods from native dll. After that you can simply add a C++/CLI managed dll to the project and use it as C# class without any DllImports and PINVOKEs. It will be a very flexible soltuion which is easy to expand. On MSDN you can find examples how to use C++/CLI.