Question

I have written an C++/Cli wrapper for a native C++ dll, but when I call some method from C# I get an System.AccessViolationException error in my C++/Cli Wrapper dll! It’s necessary to marshal the unmanaged types or something else?!

// Wrapper.h

typedef UnmanagedClass* (*Instance)(void);

private:
    UnmanagedClass *m_object; // unmanaged object   

// Wrapper.cpp

Wrapper:Wrapper()
{
    HINSTANCE unmanagedLib;
    unmangedLib = LoadLibrary(SystemStringToLPCSTR(dllPath+dllName));

    // load instance
    Instance _createInstance = (Instance)GetProcAddress(unmangedLib, "GetInstance");
    m_object = (_createInstance)(); 
}

Wrapper::~Wrapper()
{
    m_object->~UnmanagedClass();
}


Uint32 Wrapper::SomeMethod(Uint8 *bytRecvBuffer, int &iRecvLen)
{
    return m_object->SomeMethod(bytRecvBuffer, iRecvLen);
}

// Unmanaged Class

class UnmanagedClass    
{
public:
    /**
    * Default constructor. 
    */
    UnmanagedClass(void);
    /**
    * Default Destructor
    */
    ~UnmanagedClass(void);

    virtual Uint32 Wrapper::SomeMethod(Uint8 *bytRecvBuffer, int &iRecvLen);
};

// export the UnmanagedClass object
extern "C" _declspec(dllexport) UnmanagedClass* GetInstance();

// UnamangedClass.cpp

UnamangedClass::~UnamangedClass(void)
{
    if (UnamangedClassDLL != NULL)
        FreeLibrary(UnamangedClassDLL);

    UnamangedClassDLL = NULL;
}

extern "C" _declspec(dllexport) UnmanagedClass* GetInstance()
{

    return new UnmanagedClass();
}

When I call at example SomeMethod from C# I get the error in C++/Cli dll!
(I included the C++/cli dll with add reference in C sharp project and create the Wrapper object)

Thank you for your help!

greets

Answer 1

I have found the error (System.AccessViolationException):

I’m using an other object in the unmanaged code without initialization (null object -> only declared)!

Init the object with new() and all should run properly!