#include <QtWidgets>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QMenu *menu = new QMenu;
    QObject::connect(menu, &QMenu::aboutToHide, menu, &QObject::deleteLater);
    QObject::connect(menu, &QMenu::destroyed, []{ qDebug("Menu is destroyed"); });

    menu->addAction("Click me", qApp, []
    {
        QMessageBox::warning(nullptr, "Warning", "It's gonna blow!");
    });
    menu->popup(QApplication::primaryScreen()->availableGeometry().center());

    return app.exec();
}