how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver

[Alex42]

hello every one , i have an interface developed under c++ qt cretore (lineEdite ), i want to create a server that he send the data to the client every 1000ms with TCP/IP,
unfortunatly after the creation of my server and testing him withe a telnet client , I receive the data only once, but not every 1000 ms
maybe some one can helpe me to resolve the problem , thank you in advance.
attached a piece of my server code
server.cpp

server = new QTcpServer (this);

connect (server,SIGNAL (newConnection ()),this,SLOT(newConnections()));


      timer =new QTimer(this);

    timer ->start(1000);
connect (timer, SIGNAL (timeout()), this ,SLOT (newConnections(()));

if (!server ->listen(QHostAddress::Any,9000))
     {


     qDebug () << "Server could not start !";



 }
 else
     {
    //connect (timer,SIGNAL (timeout()),this,SLOT (newConnection ()));
      qDebug () << "Server started" ;

     }
void Calibration::newConnections ()
{


        QTcpSocket *socket = server->nextPendingConnection();

            socket ->waitForBytesWritten(2000);

           QTextStream T(socket);
           T <<"&& \r\n"<<"2608"<<(ui->lineEdit_17->text())<<"\r\n"<<"2609"<<(ui->lineEdit_17->text())<<"\r\n" <<"2610"<<( ui->lineEdit_17->text())<< "\r\n!!" ;
           //T <<"\r\n&& \r\n"<<(ui->lineEdit_17->text()) <<"!!\r\n!!" ;
            socket ->flush();

[KroMignon]

@Alex42 It is not a surprise that the code does not what you expect. Because it is not what you have coded.

The timer you have create will check every second if there is a new pending connection, it does not send new data on existing connection.

[Alex42]

@KroMignon , thank you for the response ,Maybe I have to change the structure of my class, because I had tested several times but nothing that works.

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

thank you for the response ,Maybe I have to change the structure of my class, because I had tested several times but nothing that works.

It is not a structure problem, it does what you have coded!

server = new QTcpServer(this);
connect(server, &QTcpServer::newConnection,this, &Calibration::newConnections, Qt::QueuedConnection);

timer = new QTimer(this);
connect(timer, QTimer::timeout, this, &Calibration::keepAlive, Qt::QueuedConnection);
timer->start(1000);

if (!server ->listen(QHostAddress::Any,9000))
{
    qDebug () << "Server could not start !";
}
else
{
    qDebug () << "Server started" ;
}

void Calibration::newConnections ()
{
   while(server->hasPendingConnections())
   {
        QTcpSocket *socket = server->nextPendingConnection();
    
        // add socket to client list (QList<QTcpSocket *> mClients (class member)
        mClients << socket;

        // remove socket from list on disconnection
        connect(socket, &QTcpSocket::disconnected, this, [this, socket]() {
            mClients.removeAll(socket);
        }, Qt::QueuedConnection);

        QTextStream T(socket);
        T <<"&& \r\n"<<"2608"<<(ui->lineEdit_17->text())<<"\r\n"<<"2609"<<(ui->lineEdit_17->text())<<"\r\n" <<"2610"<<( ui->lineEdit_17->text())<< "\r\n!!" ;
        socket->flush();
    }
}

void Calibration::keepAlive()
{
    for(const auto socket : mClients)
    {
        QTextStream T(socket);
        T <<"KeepAlive\r\n!!" ;
        socket->flush();
    }
}

Note: I use QueuedConnection to avoid threading issues and not have to add locker/mutex around the QList insert/read/remove items.

EDIT: add while loop to handle pending connections, is better because their can be more than one client requesting connection to server!

[Alex42]

unfortunately i have the same probleme

  server = new QTcpServer(this);
  connect(server, &QTcpServer::newConnection,this, &Calibration::newConnections, Qt::QueuedConnection);

  timer = new QTimer(this);
  connect(timer, SIGNAL (timeout()), this, SLOT(keepAliv()));
  timer->start(1000);

  if (!server ->listen(QHostAddress::Any,9000))
  {
      qDebug () << "Server could not start !";
  }
  else
  {
      qDebug () << "Server started" ;
  }

QList<QTcpSocket *>mClients ;

  }

  void Calibration::newConnections ()
  {

      QTcpSocket *socket = server->nextPendingConnection();

          // add socket to client list (QList<QTcpSocket *> mClients (class member)
  QList<QTcpSocket *>mClients ;
          mClients << socket;

          // remove socket from list on disconnection
          connect(socket, &QTcpSocket::disconnected, this, [this, socket]() {
           ;
          }, Qt::QueuedConnection);

          QTextStream T(socket);
          T <<"&& \r\n"<<"2608"<<(ui->lineEdit_17->text())<<"\r\n"<<"2609"<<(ui->lineEdit_17->text())<<"\r\n" <<"2610"<<( ui->lineEdit_17->text())<< "\r\n!!" ;
          socket->flush();

![alt text](image url)

  }

  void Calibration::keepAlive()
  {
       QList<QTcpSocket *>mClients ;
      for(const auto socket : mClients)
      {
          QTextStream T(socket);
          T <<"KeepAlive\r\n!!" ;
          socket->flush();
      }
  }

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

unfortunately i have the same probleme

No, the problem is different: your connect statement is wrong! You try to connect to slot keepAliv() which not exists, it is keepAlive().
To avoid this kind of error, please use new connect syntax:

// WRONG
connect(timer, SIGNAL (timeout()), this, SLOT(keepAliv()));

// CORRECT
connect(timer, SIGNAL (timeout()), this, SLOT(keepAlive()));

// EVEN MORE BETTER
connect(timer, &QTimer::timeout, this, &Calibration::keepAlive);

And, as I write in my previous post. I used Qt::QueuedConnection to avoid thread issues and not have to add locker/mutex around list access.

[Alex42]

it's the same problem, but I think the problem come from the dynamic array QList<QTcpSocket *> mClients
erreur "use of undeclared identifier mClients

void Calibration::newConnections ()
      {

          QTcpSocket *socket = server->nextPendingConnection();

              // add socket to client list (QList<QTcpSocket *> mClients (class member)
   
              mClients << socket;

              // remove socket from list on disconnection
              connect(socket, &QTcpSocket::disconnected, this, [this, socket]() {
                         mClients.removeAll(socket);
                     }, Qt::QueuedConnection);

              QTextStream T(socket);
              T <<"&& \r\n"<<"2608"<<(ui->lineEdit_17->text())<<"\r\n"<<"2609"<<(ui->lineEdit_17->text())<<"\r\n" <<"2610"<<( ui->lineEdit_17->text())<< "\r\n!!" ;
              socket->flush();


      }

      void Calibration::keepAlive()
      {
      
          for(const auto socket : mClients)
          {
              QTextStream T(socket);
              T <<"KeepAlive\r\n!!" ;
              socket->flush();
          }
      }

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

erreur "use of undeclared identifier mClients

As written in my second post, you have to declare mClients as class member of Calibration.
I suppose that Calibration is based on QObject:

class Calibration : public QObject
{
    Q_OBJECT

public:
    explicit Calibration(QObject * parent = 0):
....
private:
    QList<QTcpSocket*> mClients;
};

[Alex42]

OK resolved , but another probleme in the slot keepAlive() " no matching constuctor forinitilisation of "QTextStream"

void Calibration::keepAlive()
      {

          for(const auto socket : mClients)
          {
              QTextStream T(socket);
              T <<"KeepAlive\r\n!!" ;
              socket->flush();
          }
      }

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

OK resolved , but another probleme in the slot keepAlive() "

Yes, my fault, I correct my previous post: mClients have to be declared as QList<QTcpSocket*> not QList<QObjet*>

[Alex42]

the problem is resolved, You are The Best, Thank You Very Much for Your Help.

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

Thank You Very Much for Your Help.

your welcome

[KroMignon]

@Alex42 said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

the problem is resolved,

After rereading my code, I found a last little error.
There is a memory leak in my code, after socket is removed from mClientList it also have to deleted:

// remove socket from list on disconnection and free memory
connect(socket, &QTcpSocket::disconnected, this, [this, socket]() {
         mClients.removeAll(socket);
         socket->delateLater();
     }, Qt::QueuedConnection);

[Alex42]

@KroMignon said in how to send the data from the server to the client continuously, every 1000 ms under TCP/IP , using QTcpsocket and QTcpserver:

socket->delateLater();

deleteLater(), I added it and everything works wonderfully, thank you again.