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Variable keeps getting set to NULL after function in DLL
#include ... // various includes

    // p is NULL
    QObject *p;
    HHOOK hhk;

    BOOL WINAPI DllMain(__in HINSTANCE hinstDLL, __in DWORD fdwReason, __in LPVOID  lpvReserved)
    {
        return TRUE;
    }

    LRESULT CALLBACK MouseProc(int nCode, WPARAM wParam, LPARAM lParam)
    {
        MOUSEHOOKSTRUCT *mouseInfo = (MOUSEHOOKSTRUCT*)lParam;

        QMouseEvent::Type type;
        QPoint pos = QPoint(mouseInfo->pt.x, mouseInfo->pt.y);
        Qt::MouseButton bu;
        Qt::MouseButtons bus;
        Qt::KeyboardModifiers md = Qt::NoModifier;
        ... // very large switch statement
        // here is where i need some valid data in p
        QCoreApplication::postEvent(p, new QMouseEvent(type, pos, bu, bus, md));
        return CallNextHookEx(NULL, nCode, wParam, lParam);
    }

    // note: MOUSEHOOKSHARED_EXPORT is the same as __declspec(dllexport)
    // this function is called by the application that loads the dll
    extern "C" MOUSEHOOKSHARED_EXPORT void install(QObject *mParent, DWORD threadID, HINSTANCE hInst)
    {
        p = mParent; // p is assigned here and keeps the value of mParent untill the function returns
        hhk = SetWindowsHookEx(WH_MOUSE, MouseProc, hInst, threadID);
    } // after this function returns, p is NULL

    extern "C" MOUSEHOOKSHARED_EXPORT void uninstall()
    {
        UnhookWindowsHookEx(hhk);
    }

// EarthWidget is a class that is derived from QWidget(which is derived from QObject)
    void EarthWidget::LoadAll()
    {
        HINSTANCE DLLinst = LoadLibrary("MouseHook.dll");
        ... // get functions in DLL using GetProcAddress & typedefs, etc...
        // i pass in 'this' as mParent
        install(this, GetWindowThreadProcessId((HWND)earthplugin->GetRenderHwnd(), NULL), DLLinst);
        // note that GetWindowThreadProcessId does work and does return a valid thread id, so no problem there
     }