Is it possible to specify that in one statement ?
In theory, it seems to be possible for your scenario. At least, you can read the docs documentation about it.
Qt::UniqueConnection 0x80 This is a flag that can be combined with any one of the above connection types, using a bitwise OR. When Qt::UniqueConnection is set, QObject::connect() will fail if the connection already exists (i.e. if the same signal is already connected to the same slot for the same pair of objects). This flag was introduced in Qt 4.6.
Based on the aforementioned documentation, you would write something like this:
#include <QCoreApplication>
int main(int argc, char **argv)
{
QCoreApplication coreApplication(argc, argv);
QObject::connect(&coreApplication, SIGNAL(aboutToQuit()), &coreApplication, SLOT(quit()), static_cast<Qt::ConnectionType>(Qt::QueuedConnection | Qt::UniqueConnection));
return coreApplication.exec();
}