main.cpp

#include <QDBusInterface>
#include <QDebug>

int main()
{
    QDBusInterface kde("org.kde.ksmserver", "/KSMServer", "org.kde.KSMServerInterface", QDBusConnection::systemBus());
    kde.call("logout", 0, 3, 3);
    qDebug() << "KDE: " << kde.isValid();

    QDBusInterface gnome("org.gnome.SessionManager", "/org/gnome/SessionManager", "org.gnome.SessionManager", QDBusConnection::systemBus());
    gnome.call("Logout", 1);
    qDebug() << "Gnome: " << gnome.isValid();

    QDBusInterface xfce("org.xfce.SessionManager", "/org/xfce/SessionManager", "org.xfce.Session.Manager", QDBusConnection::systemBus());
    xfce.call("Logout", false, true);
    qDebug() << "XFCE: " << xfce.isValid();
}