main.cpp

#include <QtWidgets>

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

        QLabel label(QStringLiteral("Hello World!"));
        label.resize(250, 100);
        label.show();

        QTimer timer;
        QObject::connect(&timer, &QTimer::timeout, [&]() {
                label.setWindowTitle(QTime::currentTime().toString());
        });
        timer.start(100);
        return app.exec();
}