dllexport for an object. No Source code

[atkin]

I know this has been covered before, but what if you dont have the code for the unmanaged dll, but you know the names of all the methods as follows.
I created a c++ object and exported the funtion I wanted to use with dllexport. Then created a managed wrapper that linked with my unmanaged

code. I used c# Windows application that made use of the managed wrapper.
All this works fine. Yipee
Now i am trying to export the entire c++ object. SO i have
//------------------------------------------------------
class __declspec(dllexport) Sum
{
public:
Sum();
~Sum();
public:
double Add( double num1, double num2 );
};

//------------------------------------------------------

Is it possible to export the entire class.

Now the MC++ was

//------------------------------------------------------

extern "C"
{
double Add( double num1, double num2 );
}

//--namespace stuff and other declaration

__gc class Class1

public: double DoAdd( double n1, double n2 )
{
return Add( n1, n2 );
}

//------------------------------------------------------


My question is what do I replace the extern "C" part with now and assuming that I dont have the source code for the c++ code, just the dll and lib files.

Thanks, thanks !!!!!!