#include <qapplication.h>#include <qwidget.h>#include <qmessagebox.h>class MyMainWindow:public QWidget{ public:    MyMainWindow(); private:    QMessageBox *mbox;};MyMainWindow::MyMainWindow(){ setGeometry(100,100,200,50); mbox = new QMessageBox("Proceed ?","Do you want to proceed ?",                         QMessageBox::Critical,                         QMessageBox::Ok | QMessageBox::Default,                         QMessageBox::Cancel | QMessageBox::Escape,0); mbox->show();}main(int argc,char **argv){ QApplication a(argc,argv); MyMainWindow w; a.setMainWidget(&w); w.show(); a.exec();}