MULTICAST with QT 4.1 and above.

[jlarsj]

Hi Wysota,

Well, I have been programming those small Multicast handlers both under Linux and Windows. Actually Winsock is based also on the BSD "Like" socket lib ( Not MFC, just Winsock ), and they use the same system calls.

Well I tried using QUdpSocket but it doesn't catch any Multicasted packet. Here a simple example of code provided by Trolltech:

QUdpSocket udpSocket = new QUdpSocket(this);
udpSocket->bind(QHostAddress::LocalHost, 24001);
 
while (udpSocket->hasPendingDatagrams()) 
{
            QByteArray datagram;
            datagram.resize(udpSocket->pendingDatagramSize());
            QHostAddress sender;
            quint16 senderPort;
 
            udpSocket->readDatagram(datagram.data(), datagram.size(),
                                    &sender, &senderPort);
 
            processTheDatagram(datagram);
}

QUdpSocket udpSocket = new QUdpSocket(this);
udpSocket->bind(QHostAddress::LocalHost, 24001);

while (udpSocket->hasPendingDatagrams()) 
{
            QByteArray datagram;
            datagram.resize(udpSocket->pendingDatagramSize());
            QHostAddress sender;
            quint16 senderPort;

            udpSocket->readDatagram(datagram.data(), datagram.size(),
                                    &sender, &senderPort);

            processTheDatagram(datagram);
}

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The problem here is pretty obvious : where do you join the multicast group ????

So I tried to put in the bind() function a QHostAddress containing the multicast address, but the bind function fails each time.

So, I don't know I do believe that Qt doesn't handle multicast by itself ?? Sad isn't it