int main(int argc, char **argv)
{
    QApplication a(argc, argv);
    auto mdiArea = new QMdiArea;
    auto mdiWin1 = new QMdiSubWindow;
    mdiWin1->setWindowTitle("MDI 1");
    auto mdiWin2 = new QMdiSubWindow;
    mdiWin2->setWindowTitle("MDI 2");
    mdiArea->addSubWindow(mdiWin1);
    mdiArea->addSubWindow(mdiWin2);
    QMainWindow* mainWindow = new QMainWindow;
    mainWindow->setCentralWidget(mdiArea);
    mainWindow->show();
    return a.exec();
}