#include <QtWidgets>

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

    QWidget mainWindow;

    QDialog *dialog = new QDialog(&mainWindow);
    QBoxLayout *layout = new QBoxLayout(QBoxLayout::LeftToRight, dialog);
    QLabel *label = new QLabel("Test test test test test testtesttest testest test", dialog);
    label->setWordWrap(true);
    layout->addWidget(label);

    mainWindow.show();
    dialog->show();

    return app.exec();
}