UDP broadcast

3l3v3n

Hi, I'm finding since two days how to sent a UDP broadcast. I have seen many examples (also the broadcastReceiver and broadcastSender on the qt web site) but

their are still not working for me. When I try to send a broadcast, the method QUdpSocket::writeDatagram(..) returns -1 and the datas are not transmitted. The errorString() method returns "unable to send a message". I'm on ubuntu 14.04 x64. I wish to know if there is a particular manipulation that i should do to make this broadcast work. thanks and sorry for my english level.

Joel Bodenmann

Hello and welcome!

Is the actual Broadcast Sender example working for you?
It would be helpful if you could show us your (relevant) code.

3l3v3n

Thank for you reply. the actual example doesn't work for me.
Here is my code:

 envoyeurUDP=new QUdpSocket(this);
    recepteurUDP=new QUdpSocket(this);
    //démarrage du serveur pour UDP
    if (!recepteurUDP->bind(QHostAddress::AnyIPv4,8787,QUdpSocket::ShareAddress | QUdpSocket::ReuseAddressHint)) {
      qDebug("Impossible de créer la socket en écoute");
     exit(EXIT_FAILURE);
    }

    connect(recepteurUDP, SIGNAL(readyRead()), this, SLOT(lireDatagrams()));

void FileTransferManager::lireDatagrams(){
    
    char* donnees;
    while (recepteurUDP->hasPendingDatagrams()) {
            QByteArray datagram;
            datagram.resize(recepteurUDP->pendingDatagramSize());
            recepteurUDP->readDatagram(datagram.data(), datagram.size());
            donnees=datagram.data();
        }
}

and this one to send datagrams

void FileTransferManager::sendDatagram(string msg, QHostAddress addr){
    QByteArray datagram=msg.data();
        qint64 r=envoyeurUDP->writeDatagram(datagram.data(), datagram.size(),  addr, 7878);
}

and i use it like this :
fileManager.sendDatagram("blabla",QHostAddress::Broadcast);

3l3v3n

here is the output of my ifconfig command:

eth0 Link encap:Ethernet HWaddr f8:a9:63:2d:89:ff
UP BROADCAST MULTICAST MTU:1500 Metric:1 Packets reçus:0 erreurs:0 :0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:1000 Octets reçus:0 (0.0 B) Octets transmis:0 (0.0 B)

lo Link encap:Boucle locale
inet adr:127.0.0.1 Masque:255.0.0.0 adr inet6: ::1/128 Scope:Hôte UP LOOPBACK RUNNING MTU:65536 Metric:1 Packets reçus:5311 erreurs:0 :0 overruns:0 frame:0 TX packets:5311 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:0 Octets reçus:661728 (661.7 KB) Octets transmis:661728 (661.7 KB)

wlan0 Link encap:Ethernet HWaddr b8:ee:65:ab:4f:77
inet adr:10.42.0.1 Bcast:10.42.0.255 Masque:255.255.255.0 adr inet6: fe80::baee:65ff:feab:4f77/64 Scope:Lien UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 Packets reçus:14069 erreurs:0 :0 overruns:0 frame:0 TX packets:15529 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:1000 Octets reçus:6007592 (6.0 MB) Octets transmis:2307422 (2.3 MB)

SGaist

Hi and welcome to devnet,

How do you know it doesn't work ?

3l3v3n

writedatagram() returns -1 ,error() returns SocketError::NetworkError

SGaist

I've missed a point in one of your answer. Did I understand correctly that the "Broadcast Sender Example" failed for you ?

If so, then before trying to debug your application, you should check what makes the example fail. The code doesn't mix both sending and receiving.

LuGRU

What's size of data? If it's > 512 bytes it will fail.