Question

OK, so I have a situation in which I call LoadLibrary on a DLL that I wrote. This call to LoadLibrary returns error #998, or ERROR_NOACCESS “Invalid access to memory location.”

The DLL in question uses MFC in one configuration, and not in another; only the MFC configuration has this problem. It used to work, but I have no idea what I changed: I’d actually moved on to the non-MFC version and been tinkering quite a lot with that and I have no idea what I could have done that affected the MFC version.

I don’t know a lot about DLLs. The original loading code was actually given to me, and I haven’t changed it. Below is that code:

// submodule loading
#ifndef MFC
// Project uses standard windows libraries, define an entry point for the DLL to handle loading/unloading
BOOL WINAPI DllMain(HANDLE hDllHandle, DWORD dwReason, LPVOID lpreserved)
{
    _MESSAGE("DllMain called.");
    switch(dwReason)
    {
    case DLL_PROCESS_ATTACH:    // dll loaded
        hModule = (HMODULE)hDllHandle;  // store module handle
        _MESSAGE("Attaching Submodule ..."); 
        break;
    case DLL_PROCESS_DETACH:    // dll unloaded
        _MESSAGE("Detaching Submodule ...");      
        break;
    }   
    return true;
}
#else
// Project uses MFC, we define here an instance of CWinApp to make this a 'well-formed' DLL
class CSubmoduleApp : public CWinApp
{
public:
    virtual BOOL InitInstance()
    {// dll loaded
        hModule = m_hInstance;  // store module handle
        _MESSAGE("Attaching Submodule ...");
        return true;
    }
    virtual int ExitInstance()
    {// dll unloaded
       _MESSAGE("Detaching Submodule ...");      
       return CWinApp::ExitInstance();
    }
} gApp;
#endif

Obviously, MFC is defined in the MFC configuration, and not otherwise.

I doubt this is enough information to solve this problem; I realize that. What I’m actually hoping to learn is where to look for problems that might cause this error. I’ll be happy to supply any information you need — once I know it’s needed.

Thanks for any tips.

Answer 1

OK, this question was answered by a friend of mine (no idea if he has a StackOverflow account; not going to pester him with answering it twice).

The deal is that I had a global object, the class of which had a constructor that called a function that depended upon another global object (ironically enough, the function in question was _MESSAGE, but by the time DllMain or InitInstance gets called, that function works fine). C++ doesn’t allow you to specify the order in which globals get initialized, so when this global’s constructor got run (when the computer attempted to load the DLL), it caused a memory error by attempting to use another global that hadn’t been created yet.

So… that’s the answer. A really specific case, but I guess if anyone else finds they’re getting 998 errors and need to know what sorts of problems to check, this is something to look for: make sure all your globals are independent!