std::string in C#?

Question

Hello,

I thought the problem is inside my C++ function,but I tried this

C++ Function in C++ dll:

bool __declspec( dllexport ) OpenA(std::string file)
{
return true;
}

C# code:

[DllImport("pk2.dll")]
public static extern bool OpenA(string path);

    if (OpenA(@"E:\asdasd\"))

I get an exception that the memory is corrupt,why?

If I remove the std::string parameter,it works great,but with std::string it doesnt work.

Answer 1

std::string and c# string are not compatible with each other. As far as I know the c# string corresponds to passing char* or wchar_t* in c++ as far as interop is concerned.
One of the reasons for this is that There can be many different implementations to std::string and c# can't assume that you're using any particular one.

Answer 2

Maybe you can solve it by making a managed c++ bridge that unpacks the string? Here is a SO question about this subject.

Answer 3

Try something like this:

bool __declspec( dllexport ) OpenA(const TCHAR* pFile)
{ 
   std::string filename(pFile);
   ...
   return true;
}

You should also specify the appropriate character set (unicode/ansi) in your DllImport attribute.

As an aside, unrelated to your marshalling problem, one would normally pass a std:string as a const reference: const std:string& filename.

Answer 4

It's not possible to marshal a C++ std::string in the way you are attempting. What you really need to do here is write a wrapper function which uses a plain old const char* and converts to a std::string under the hood.

C++

extern C { 
  void OpenWrapper(const WCHAR* pName) {
    std::string name = pName;
    OpenA(name);
  }
}

C#

[DllImport("pk2.dll")]
public static extern void OpenWrapper( [In] string name);