#include <QApplication>
#include <QTabWidget>
#include <QLabel>
#include <QMainWindow>
#include <QFont>

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

QApplication app(argc, argv);

QMainWindow *window = new QMainWindow;

QFont font = app.font();
font.setPointSize(6);
app.setFont(font);

QLabel *label = new QLabel;
label->setText("This is a text label");

QTabWidget *tabs = new QTabWidget;
tabs->addTab(label, "This is a tab");

window->setCentralWidget(tabs);

window->show();
window->raise();
return app.exec();
}