Export native type from C++/CLI project

Question

How do I export the methods of a native class defined in a C++/CLI project? Here's what I have:

The .h file:

#pragma once

#ifdef COMPILE_PRODUCER_LIB
  #define PRODUCER_LIB_EXPORT __declspec(dllexport)
#else
  #define PRODUCER_LIB_EXPORT __declspec(dllimport)
#endif

public class PRODUCER_LIB_EXPORT MySecondNativeClass {
public:
  MySecondNativeClass(int val);

  int getValue() const;

private:
  int m_value;
};

The .cpp file:

#include "stdafx.h"
#include "MySecondNativeClass.h"

MySecondNativeClass::MySecondNativeClass(int val) {
  this->m_value = val;
}

int MySecondNativeClass::getValue() const {
  return this->m_value;
}

Using this class in the same project works fine, but using it in another (C++/CLI) project gives me "unresolved external symbol" linker errors. (COMPILE_PRODUCER_LIB is a preprocessor definition defined only in the project that contains the class.)

I've created a small solution (for Visual Studio 2010) that shows the problem (download at the end of this page). There, the native class MySecondNativeClass is defined in the project "ManagedProviderLib" and is being used in "ExternalTestClass.cpp" (in project "ManagedExternalLib").

Answer 1

Your DLL project creates a .lib file in the build directory, the DLL's import library. You need to specify that .lib file in the other project, Linker + Input, Additional Dependencies setting.

Note that Add Reference cannot work, the assembly metadata only contains definitions for managed classes. Your class is native C++, not managed. Also make sure that your .cpp file is compiled without /clr in effect. The C++/CLI compiler will happily translate native C++ classes to IL but that is not very efficient. You can control this within the source code file with #pragma managed.