QUdpSocket: Program send but do not receive - c++

Question

I have problem with QUdpSocket. I want to create a simple program to send and receive data using the UDP protokol. I already read many similar topic but I do not found solved. Communication worked only for QHostAdress::LocalHost, then I give this same data as send, but if I want to send data to outside set concrete address, for example 194.181.161.134, that does not worked. That mean data is send but I can't receive. This is my code:
class Okno_GL : public QMainWindow
{
Q_OBJECT
public:
explicit Okno_GL(QWidget *parent = 0);
QWidget *wg;
QPushButton *pb;
QPushButton *pl;
QGridLayout *gr;
QUdpSocket *socket;
QHostAddress host;
QHostAddress bcast;
signals:
public slots:
void SLOT_Write();
void SLOT_load();
};
class Receiver : public QObject
{
Q_OBJECT
public:
Receiver();
QUdpSocket *udpSocket;
public slots:
void SLOT_processPendingDatagrams();
void SLOT_StCh(QAbstractSocket::SocketState state);
};
Okno_GL::Okno_GL(QWidget *parent) :
QMainWindow(parent)
{
pb = new QPushButton("write" , this);
pl = new QPushButton("read" , this);
wg = new QWidget(this);
setCentralWidget(wg);
gr = new QGridLayout(wg);
gr->addWidget(pb);
gr->addWidget(pl);
socket = new QUdpSocket(this);
connect(pb , SIGNAL(clicked()) , SLOT(SLOT_Write()));
connect(pl , SIGNAL(clicked()) , SLOT(SLOT_load()));
}
void Okno_GL::SLOT_Write()
{
QByteArray datagram = "gS";
int send;
send = socket->writeDatagram(datagram.data(), QHostAddress("194.181.161.134"), 1200);
}
void Okno_GL::SLOT_load()
{
}
Receiver::Receiver()
{
udpSocket = new QUdpSocket(this);
connect(udpSocket, SIGNAL(stateChanged(QAbstractSocket::SocketState)) , this , SLOT(SLOT_StCh(QAbstractSocket::SocketState)));
if(udpSocket->bind(QHostAddress::Any , 1200))
{
qd "bind";
}
else
{
qd "not bind";
}
}
void Receiver::SLOT_processPendingDatagrams()
{
qd "receiver";
QByteArray datagram;
do {
datagram.resize(udpSocket->pendingDatagramSize());
udpSocket->readDatagram(datagram.data(), datagram.size());
} while (udpSocket->hasPendingDatagrams());
qd "datagram" << datagram;
}
void Receiver::SLOT_StCh(QAbstractSocket::SocketState state)
{
qd "slot" << state;
QByteArray datagram = "gS";
if ( state == QAbstractSocket::BoundState ) {
connect(udpSocket, SIGNAL(readyRead()), this, SLOT(SLOT_processPendingDatagrams()) , Qt::QueuedConnection);
}
}

Answer 1

You should use write() instead of writeDatagram()
qint64 QUdpSocket::writeDatagram(const char * data, qint64 size, const QHostAddress & address, quint16 port)
Warning: Calling this function on a connected UDP socket may result in
an error and no packet being sent. If you are using a connected
socket, use write() to send datagrams.

Answer 2

So, I rebuild my code accordingly with your proposition. I add this line in construktor class Okno_GL.
socket = new QUdpSocket(this);
socket->connectToHost(QHostAddress("194.181.161.134") , 1200);
Here is slot to send
void Okno_GL::SLOT_Write()
{
QByteArray datagram = "gS";
int send;
// send = socket->writeDatagram(datagram.data(), QHostAddress("194.181.161.134"), 1200);
send = socket->write(datagram);
qd " send" << send;
}
Receiver code is not change, so I still white for signal readRedy() ,and I do not get him after send data.
PS. I whant to add that I have other option to connetc, is very very simply file command *bat whitch connect this host without any problem . This is proof that my network or admin nothing blocks (port , ip);
Pss thanks for your interest
Problem solved ! It is very stupid mistake. I should be send 3 bajt instead 2. The 3 bajt it is 0x0D.
Following code is work
socket = new QUdpSocket(this);
socket->bind(QHostAddress::Any, 1200);
and send
QByteArray datagram = "gS";
datagram.append(0x0D);
int send;
send = socket->writeDatagram(datagram.data(), QHostAddress("194.181.161.134"), 1200);
and receive after signal readyRead()
qd "receiver";
QByteArray datagram;
do {
datagram.resize(socket->pendingDatagramSize());
socket->readDatagram(datagram.data(), datagram.size());
} while (socket->hasPendingDatagrams());
qd "datagram" << datagram;
very help mi wireshark. Thanks for all