Question

I have compiled and built a DLL project in VS 2010. I have an added sister-project to the same solution which will essentially link to the above DLL and need to load its constructor and functionalities. However, as soon as I am trying to instantiate the object, it gives access violation.

In main, I do this..

#include <iostream>
#include "MCaromDLL.h"

using namespace std;
using namespace MagneticCarom;

int main() {
    . . .
    MagneticCaromWrapper wrapper;
        . . .
}

My “MCaromDLL.h” looks like this:

// MCaromDLL.h

#define NULL 0
#define MAX_COLS 201        //Fixed based on the FEMM values
#define MAX_ROWS MAX_COLS   //Fixed based on the FEMM values

#ifdef DLL_PROJECT 
#define DLLSPEC __declspec(dllexport)
#else
#define DLLSPEC __declspec(dllimport)
#endif

#ifndef __MCAROMDLL_H__
#define __MCAROMDLL_H__

namespace MagneticCarom
{
    . . . . . . .
    class DLLSPEC MagneticCaromWrapper
    {
        private:
                       //All private members here...            

        public:
            MagneticCaromWrapper();

            MagneticCaromWrapper(int number);

            virtual ~MagneticCaromWrapper();

                        //remaining functions
    }
}
#endif

Note that I am trying to export the entire class (although I tried exporting individual funcs also, but in vain) now. The entire code can be made available on request.

Answer 1

Its always an issue to handle memory or structs over dll interface.
Things that can go wrong:

• Different runtime
• Different allignment
• Overloaded new …

To make sure it works:
– Use a pure virtual interface
– Use a factory method
– Use a delete/release method

IMagneticCaromWrapper* DLLSPEC FactoryMagneticCaromWrapper();

class IMagneticCaromWrapper
{
public:
    virtual void Release();
}

with an implementation.

IMagneticCaromWrapper* DLLSPEC FactoryMagneticCaromWrapper()
{
    return new MagneticCarom();
}

IMagneticCaromWrapper::Release()
{
    delete this;
}

At best do not throw exceptions cross dll boundaries.