this is the part of QAbstractSocket.cpp

Qt-4.4.2 code:

This function is called after connectToHost(...)

void QAbstractSocketPrivate::_q_startConnecting(const QHostInfo &hostInfo)
{
    ...
    addresses = hostInfo.addresses();
	...

    // Try all addresses twice.        WHAT FOR?
    addresses += addresses;

    if (addresses.isEmpty()) {         HERE THE ERROR SIGNAL MUST BE EMITTED, BUT...
        ...
        state = QAbstractSocket::UnconnectedState;
        socketError = QAbstractSocket::HostNotFoundError;
        q->setErrorString(QLatin1String(QT_TRANSLATE_NOOP("QAbstractSocket", "Host not found")));
        emit q->stateChanged(state);
        emit q->error(QAbstractSocket::HostNotFoundError);
        return;
    }

	...
	
    // Report the successful host lookup   WHY HERE & WHERE IS THE SUCCESS? O_o
    emit q->hostFound();

    ...
	
>>> _q_connectToNextAddress();
}


void QAbstractSocketPrivate::_q_connectToNextAddress()
{
    ...
        // Start the connect timer.
        if (threadData->eventDispatcher) {
            if (!connectTimer) {
                connectTimer = new QTimer(q);
                QObject::connect(connectTimer, SIGNAL(timeout()),
                                 q, SLOT(_q_abortConnectionAttempt()),
                                 Qt::DirectConnection);
            }
>>>         connectTimer->start(QT_CONNECT_TIMEOUT);
        }
		
    ...
}


void QAbstractSocketPrivate::_q_abortConnectionAttempt()
{
    ...
    if (socketEngine) {
        socketEngine->setWriteNotificationEnabled(false);

        if (socketEngine->isValid())
>>>         _q_testConnection();
    }
}

void QAbstractSocketPrivate::_q_testConnection()
{
    if (socketEngine) {
        if (socketEngine->state() != QAbstractSocket::ConnectedState) {
            // Try connecting if we're not already connected.
            if (!socketEngine->connectToHost(host, port)) {
                if (socketEngine->error() == QAbstractSocket::UnfinishedSocketOperationError) {
                    // Connection in progress; wait for the next notification.
                    socketEngine->setWriteNotificationEnabled(true);
>>>                 return;              SEE U IN _q_abortConnectionAttempt() & SO ON
                }
            }
        }

        if (threadData->eventDispatcher) {
            if (connectTimer)
                connectTimer->stop();
        }

    }
}

Qt-4.2.2 code:

void QAbstractSocketPrivate::_q_testConnection()
{

    if (threadData->eventDispatcher) {
        if (connectTimer)
            connectTimer->stop();
    }

    if (socketEngine && (socketEngine->state() == QAbstractSocket::ConnectedState || socketEngine->connectToHost(host, port))) {
        fetchConnectionParameters();
        return;
    }

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::_q_testConnection() connection failed,"
           " checking for alternative addresses");
#endif
    _q_connectToNextAddress();
}