Question

I’m trying to use a C++ class from a native .dll project in a C++/CLI .dll project. Visual Studio 2010, .NET Framework 3.5. So far this is what I have:

// This is a common macro:
#ifdef ISDLL
#define DLL __declspec(dllexport)
#else
#define DLL __declspec(dllimport)
#endif

NativeProject:
   //INativeType.h: 
   class DLL INativeType {
       public:
           virtual void Foo() = 0;
   };

    //NativeType.h: 
    class DLL NativeType : public INativeType {
        public:
            virtual void Foo(); 
    };

    extern "C" DLL INativeType CreateNativeType();

    //NativeType.cpp: 
    void NativeType::Foo() {} 
    extern "C" DLL INativeType* CreateNativeType() { 
        return new NativeType(); 
    }

C++/CLI Project:
    // Wrapper.h:
    #include "INativeType.h"
    ref class Wrapper {
        INativeType* m_nativeType;
    };

    // Wrapper.cpp:
    #include "Wrapper.h"
    #include "NativeType.h"
    // in some method:
        m_nativeType = CreateNativeType();

This gives me the following linker error:

error LNK2028: unresolved token (...) "extern "C" class INativeType * __stdcall CreateNativeType(void)"" ... in Wrapper.obj

Also, although the functions are correctly exported in NativeProject.dll, as I verified it with DependencyWalker, the linker also gives this warning:

warning LNK4199: /DELAYLOAD:NativeProject.dll ignored; no imports found from NativeProject.dll

The C++/CLI project is configured to delay load NativeProject.dll and also includes NativeProject.lib in its linker options. At this point I don’t know how to diagnose this linker error. What am I doing wrong?

Answer 1

Why don’t you just let the C++/CLI project instantiate the class directly instead of with a factory method?

Besides that, it just looks like you are re-inventing COM (using objects through interfaces). I would just instantiate full-blown C++ classes or, if you really need it, use full-blown COM.

EDIT: Make sure the factory method’s calling convention is the same in both the client and the DLL.