Question

This wasn’t immediately clear to me from the docs for QCoreApplication::quit().

Are any pending events in the event loop cancelled when the quit() slot is invoked?

Answer 1

Calling QCoreApplication::quit() is the same as calling QCoreApplication::exit(0). There it says

After this function has been called, the application leaves the main event loop and returns from the call to exec().

Since the event loop is left, I would think any pending events are cancelled.

Edit: I made a small test case to show that pending events are indeed cancelled:

#include <QCoreApplication>
#include <QTimer>
#include <QDebug>

class MyObject : public QObject
{
        Q_OBJECT

    public Q_SLOTS:

        void start()
        {
            QCoreApplication::postEvent(this, new QEvent(QEvent::User));
            QCoreApplication::quit();
        }

    protected:

        void customEvent(QEvent* event)
        {
            qDebug() << "Event!";
        }

};

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

    MyObject o;
    QTimer::singleShot(0, &o, SLOT(start()));

    return app.exec();
}

#include "main.moc"

In this case, the event posted in MyObject::start() will never arrive. It will, of course, if you remove the call to QCoreApplication::quit().