#include <QtWidgets/QtWidgets>

Q_IMPORT_PLUGIN(QWindowsIntegrationPlugin);
Q_IMPORT_PLUGIN(QWindowsVistaStylePlugin);


class Instance
{
private:
    Instance();
public:
    ~Instance();
public:
    static Instance* Init()
    {
        //!! notice the static keyword !!
        static class Instance instance;
        return &instance;
        // return new class Instance();
    }
private:
    class RuntimeHost
    {
    public:
        RuntimeHost();
        ~RuntimeHost();
    private:
        int qt_app_argc_ = 1;
        char* qt_app_argv_[2] = {nullptr, nullptr};
    private:
        char* qt_app_argv_0_ = nullptr;
        class QCoreApplication* qt_app_ = nullptr;
    private:
        class QLabel* qt_widget_ = nullptr;
    public:
        auto Execute() const {
            qt_widget_->show();
            return qt_app_->exec();
        }
    };
private:
    class RuntimeHost* runtime_host_ = nullptr;
public:
    int Run() {
        return runtime_host_->Execute();
    }
};


Instance::Instance()
{
    printf("%s\n", __FUNCTION__);
    runtime_host_ = new class RuntimeHost();
}


Instance::~Instance()
{
    delete runtime_host_;
    printf("%s\n", __FUNCTION__);
}


Instance::RuntimeHost::RuntimeHost()
{
    printf("%s\n", __FUNCTION__);

    qt_app_argv_0_ = new char[10](); //"Test.exe";
    qt_app_argv_0_[0] = 'T';
    qt_app_argv_0_[1] = 'e';
    qt_app_argv_0_[2] = 's';
    qt_app_argv_0_[3] = 't';
    qt_app_argv_0_[4] = '.';
    qt_app_argv_0_[5] = 'e';
    qt_app_argv_0_[6] = 'x';
    qt_app_argv_0_[7] = 'e';
    qt_app_argv_0_[8] = 0;

    qt_app_argv_[0] = qt_app_argv_0_;

    printf("%s\n", "new QApplication");
    qt_app_ = new QApplication(qt_app_argc_, qt_app_argv_);

    printf("%s\n", "new QLabel");
    qt_widget_ = new QLabel("Hello World");
    qt_widget_->setAlignment(Qt::AlignCenter);
    qt_widget_->setMinimumSize(QSize(646, 482));
}


Instance::RuntimeHost::~RuntimeHost()
{
    printf("%s\n", "delete QLabel");
    delete qt_widget_;
    printf("%s\n", "delete QApplication");
    delete qt_app_;
    delete[] qt_app_argv_0_;
    printf("%s\n", __FUNCTION__);
}


int
main(int /*argc*/, char* /*argv*/[])
{
    // crash for `static class Instance instance`
    return Instance::Init()->Run();

    /*
    // ok for `return new class Instance()`
    auto instance = Instance::Init();
    auto res = instance->Run();
    delete instance;
    return res;
    */
}