QT - QTcpSocket read and write data continuously, Client always receives empty string

Ayse

I'm using QT 4.8.6 and I'm beginner level at QT. I look at the Fortune Client-Server Example. In this example , data is sent with button click action. But I want to send data continuously in Server Side and read this continuous data in Client Side. How can I implement this code in QT ?

I implemented this code block for continuously data flow , but I can't send data between client and server. When I was sending data from server, client got this data "", always receives empty string .

In Server Side :

class ProducerThread : public QThread
{
public :
int socketDescriptor;
ProducerThread(int socketDescriptor,  QObject *parent)
    : QThread(parent), socketDescriptor(socketDescriptor)
{

}
void run()
{
    QTcpSocket tcpSocket;
    if (!tcpSocket.setSocketDescriptor(socketDescriptor)) {
        //emit error(tcpSocket.error());
        return;
    }
    while(true)
    {
        QString deneme = " test ";
        QByteArray block;
        QDataStream out(&block, QIODevice::WriteOnly);
        out.setVersion(QDataStream::Qt_4_0);            
        out << (quint16)0;
        out <<deneme;
        out.device()->seek(0);
        out << (quint16)(block.size() - sizeof(quint16));         
        tcpSocket.write(block);
        tcpSocket.flush();//writes as much as possible            
    }
}};
class ProducerServer :public QTcpServer
{
private:
public:
ProducerServer(QObject *parent=0)
    : QTcpServer(parent)
{

}
protected:
void incomingConnection(int socketDesc)
{
    ProducerThread *thread = new ProducerThread(socketDesc, this);
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
    thread->start();        
}
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

ProducerServer server;
if (!server.listen(QHostAddress::LocalHost,12345)) {
    qDebug()<<"Threaded  Server"<<
          "Unable to start the server:";

}
return a.exec();
}

In Client Side :

ConsumerThread.h

#ifndef CONSUMERTHREAD_H
#define CONSUMERTHREAD_H

#include <QObject>
#include <QtNetwork>

class ConsumerThread : public QThread
{
    Q_OBJECT
public:
    explicit ConsumerThread(QObject *parent = 0);
    void run();
    QTcpSocket *tcpSocket;
    int blockSize;

signals:

public slots:
void mySocketRead();

};

#endif // CONSUMERTHREAD_H

ConsumerThread.cpp

#include "consumerthread.h"

ConsumerThread::ConsumerThread(QObject *parent) :
    QThread(parent)
{
    blockSize = 0;
    tcpSocket = new QTcpSocket;
    tcpSocket->connectToHost(QHostAddress::LocalHost,12345);
}
void ConsumerThread::run()
{
    connect(tcpSocket,SIGNAL(readyRead()), this, SLOT( mySocketRead()));

}
void ConsumerThread::mySocketRead(){
    qDebug() <<"here C1 bytes = " << tcpSocket->bytesAvailable();
    blockSize = 0;
    QDataStream in(tcpSocket);
    in.setVersion(QDataStream::Qt_4_0);

    qDebug() << "Bytes available : " << tcpSocket->bytesAvailable();

    QString nextFortune;
    in >>nextFortune;
    qDebug() << nextFortune;

}

aha_1980

Hi @Ayse, welcome to devnet!

But I want to send data continuously in Server Side and read this continuous data in Client Side. How can I implement this code in QT ?

Then better have a look at the loopback example

Any reason you have to do this in a thread? After all, it makes things more difficult for starters.

Regards

Ayse

@aha_1980 Thanks for your answer. I have to do this thread because I want to send continuous data without blocking main program.

aha_1980

@Ayse said in QT - QTcpSocket read and write data continuously, Client always receives empty string:

I have to do this thread because I want to send continuous data without blocking main program.

No, you don't need threads for that.

Ayse

@aha_1980 @aha_1980 Is it possible listen and write operations at the same time ? In Java, I have to use threads for this operations and now I try it in QT C++.

aha_1980

Hi @Ayse

Qt uses Signals&Slots for that. Effectively, writing and reading sockets is non-blocking. Just look at the example I gave you.

Ayse

@aha_1980 @aha_1980 @aha_1980 Thank you all for your replies.

Regards..

aha_1980

@Ayse You're welcome :)