Access violation in MFC dll (wrapped in C++/CLI) s

Question

I have written an managed C++/CLI wrapper for mfc dll (C++) and have some access violations after second call of dll!

Wrapper

// in .h
typedef CKeyManagerServerApp* (*KeyManagerInstance)(CCommonUtils *);

ManagedKeyInterface::ManagedKeyInterface()
{
    HINSTANCE m_keyManagerLib = LoadLibrary("pathToDll");

    KeyManagerInstance _createInstance = (KeyManagerInstance)GetProcAddress(m_keyManagerLib, "GetInstance");

    // get native reader interface from managed reader interface
    CCommonUtils *nativeReaderInterface = static_cast<CCommonUtils*>(readerInterface->nativeReaderInterface.ToPointer());

    CKeyManagerServerApp *m_keyManagerApp = (_createInstance)(nativeReaderInterface );
}

ManagedKeyInterface::~ManagedKeyInterface()
{
    try
{
    DestroyKeyManagerInstance _destroyInstance = (DestroyKeyManagerInstance)GetProcAddress(m_keyManagerLib, "DestroyInstance");
    (_destroyInstance)(m_keyManagerApp);

    FreeLibrary(m_keyManagerLib);           
}
    catch(System::Exception ^e)
    {
        FreeLibrary(m_keyManagerLib);
    }
}

NATIVE MFC CLASS

extern "C" _declspec(dllexport) CKeyManagerServerApp* GetInstance(CCommonUtils *readerInterface)
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());

    return new CKeyManagerServerApp(readerInterface);
}

extern "C" _declspec(dllexport) void DestroyInstance(CKeyManagerServerApp *ptr)
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());

    delete ptr;
}

// constructor
CKeyManagerServerApp::CKeyManagerServerApp(CCommonUtils *readerInterface)   
{
    m_log = new Logging(loggingFilePath); // <--- ERROR at second call


    // reader interface object for communication 
    m_readerComm = new ReaderCommunication(readerInterface, m_log); 

    m_smartmaskcmds = new CSmartMaskCmds(m_readerComm, m_log);

    readerInterface = NULL;
}

// destructor
CKeyManagerServerApp::~CKeyManagerServerApp()
{
    // destruct objects     
    delete m_smartmaskcmds; 
    delete m_readerComm;    
    delete m_log;   
}

in ReaderCommunication and CSmartMaskCmds constr. the object will only assigned!

At first runtime of the C# program (loaded the wrapper with add reference) everything works fine, but when I start it again I get:

First-chance exception at 0x76f85b57 in TestKeyManagerApp.exe: 0xC0000005: Access violation reading location 0xdddddddd. First-chance exception at 0x75169617 in TestKeyManagerApp.exe: Microsoft C++ exception: CMemoryException at memory location 0x0024e820..

when I call m_log = new Logging(loggingFilePath)

It seems the destructor does not work right!?

Any ideas!!??

Thank you!

Answer 1

when I call m_log = new Logging(loggingFilePath)

What's happening behind the scenes? Find out where exactly it crashes. Enable unmanaged debugging if you are using C#. I guess the problem is under Logging constructor.

Answer 2

When you see the value 0xdddddddd, it means that some pointer was deleted (VC will set that value on debug builds to help you recognize these cases). You don't tell us what's loggingFilePath and how Logging is implemented, but my guess is that loggingFilePath is deleted at some point, and Logging tries to access its value or a virtual function in the constructor (or initialization list).

This could also explain the crash in the destructor - you're deleting m_log, which probably holds an illegal pointer it got from loggingFilePath. When you try to use it again, you get the same crash.