#include <QtCore>
#include <QtGui>
#include <QtWidgets>

class Widget : public QWidget
{
    Q_OBJECT

private slots:
    void updateGeometry()
    {
        QRect rc = QApplication::desktop()->availableGeometry();

        move(rc.topLeft());
        resize(rc.size());
    }

public:
    Widget() : QWidget()
    {
        updateGeometry();

        connect(QApplication::desktop(), SIGNAL(resized(int)), this, SLOT(updateGeometry()));

        show();
    }
};

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

    new Widget;

    return app.exec();
}

#include "main.moc"

QBackingStore::flush() called for  QWidgetWindow(0x923a358, name = "WidgetClassWindow")  which does not have a handle.
Segmentation fault (core dumped)

BackingStore::flush() called for  QWidgetWindow(0x8080820, name = "WidgetClassWindow")  which does not have a handle.
                                                                                                                     Program received signal SIGSEGV, Segmentation fault.
0xb6c97b14 in QScreen::handle() const () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Gui.so.5
(gdb) bt
#0  0xb6c97b14 in QScreen::handle() const () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Gui.so.5
#1  0xb4c0cbee in ?? () from /opt/Qt-5.4.0/5.4/gcc/plugins/platforms/libqxcb.so
#2  0xb6e40c56 in QBackingStore::resize(QSize const&) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Gui.so.5
#3  0xb7a5b1e5 in ?? () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#4  0xb7a5c79c in ?? () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#5  0xb7a82015 in QWidgetPrivate::syncBackingStore() () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#6  0xb7a913ad in QWidget::event(QEvent*) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#7  0xb7a4e054 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#8  0xb7a51a6b in QApplication::notify(QObject*, QEvent*) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#9  0xb76f6a7e in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#10 0xb76f9ae0 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#11 0xb76fa043 in QCoreApplication::sendPostedEvents(QObject*, int) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#12 0xb7758104 in ?? () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#13 0xb6a781e3 in g_main_context_dispatch () from /lib/i386-linux-gnu/libglib-2.0.so.0
#14 0xb6a78468 in ?? () from /lib/i386-linux-gnu/libglib-2.0.so.0
#15 0xb6a78528 in g_main_context_iteration () from /lib/i386-linux-gnu/libglib-2.0.so.0
#16 0xb7758538 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#17 0xb4c625c6 in ?? () from /opt/Qt-5.4.0/5.4/gcc/plugins/platforms/libqxcb.so
#18 0xb76f44b6 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#19 0xb76f492c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#20 0xb76fa0e9 in QCoreApplication::exec() () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Core.so.5
#21 0xb6c634f4 in QGuiApplication::exec() () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Gui.so.5
#22 0xb7a47464 in QApplication::exec() () from /opt/Qt-5.4.0/5.4/gcc/lib/libQt5Widgets.so.5
#23 0x08049f22 in main (argc=1, argv=0xbffff004) at main.cpp:36