You mean that there it need to create 3 different sockets and bind it.

Yep, you're right - I meant three separate sockets, each bound once :)

Cheers.

I want to bind fixed 3 IP addresses only.

As far as I know, the underlying OS sockets (on Linux, at least) only support one or all interfaces for a single bind. Qt probably doesn't extend on that.

So I think you would need to have three separate UDP binds, but you can connect them all to the same slot anyway, like:

MyClass::MyClass() {
    for (const QHostAddress &address, addresses) {
        QUdpSocket * const socket = new QUdpSocket(this);
        connect(socket, SIGNAL(readyRead()), this, SLOT(mySlot()));
        socket->bind(address, 12345);
    }
}

void MyClass::mySlot() {
    QUdpSocket * const socket = qobject_cast<QUdpSocket *>(sender());
    Q_CHECK_PTR(socket);
    // do stuff with socket.
}

Cheers.