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Thread: Using QTcpSocket to receive binary data

  1. #1
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    Default Using QTcpSocket to receive binary data

    Hi,

    I wolud like to connect via ethernet with microcontroller. At the beginning i try with an example broadcast receiver and only think i change was
    Qt Code:
    1. QHostAddress address;
    2. address.setAddress(QString("192.168.20.1"));
    3. udpSocket->bind(address, QUdpSocket::ShareAddress);
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    Next i try use telnet (hyperterminal) to connect and send some data. I sets the same address like in qt, connect using: TCP/IP (Winsock) and port number 23. But the hyperterminal shows message window with Unable to connect.
    And my first question is how to send some data (binary or string) from application like hyperterminal (maybe other) to gui in qt using ethernet (QNetwork). Maybe is some software allows me to put some data to chosen address.

    Secondly i try to write my code but now using tcp/ip socket, not udp.
    Qt Code:
    1. void MainWindow::receivData()
    2. {
    3. if (receivSocket->waitForConnected(3000))
    4. {
    5. qDebug() << "Connected";
    6. }
    7. QByteArray buffer = receivSocket->read();
    8. bool ok;
    9. int data = buffer.toInt(&ok,10);
    10. ui->label->setText(QString::number(data));
    11. }
    12.  
    13. MainWindow::MainWindow(QWidget *parent) :
    14. QMainWindow(parent),
    15. ui(new Ui::MainWindow)
    16. {
    17. ui->setupUi(this);
    18. receivSocket = new QTcpSocket(this);
    19. connect(receivSocket,SIGNAL(readyRead()),this,SLOT(receivData()));
    20. QHostAddress address;
    21. address.setAddress(QString("192.168.20.1"));
    22. receivSocket->connectToHost(address,QIODevice::ReadOnly);
    23. }
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    and in .h
    Qt Code:
    1. #include <QtNetwork/QTcpSocket>
    2. ...
    3. private:
    4. QTcpSocket *receivSocket;
    5. private slots:
    6. void receivData();
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    I try to compile it but are some errors. error: no matching function for call to 'QTcpSocket::read()' Follow http://doc.qt.nokia.com/latest/network-programming.html QTcpSocket contains read(). My second question is what i should add/change in code if i want to receive some data.
    Thanks in advance for any help.

  2. #2
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    Default Re: Using QTcpSocket to receive binary data

    Telnet uses TCP not UDP so trying to marry the two was never going to work.

    QTcpSocket does not contain a read() method that takes no arguments, which what your compiler is telling you about your code.

  3. #3
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    Default Re: Using QTcpSocket to receive binary data

    Quote Originally Posted by ChrisW67 View Post
    QTcpSocket does not contain a read() method that takes no arguments, which what your compiler is telling you about your code.
    Ok. I change it to correct form. But now when i'm debugging i gets errors:
    Qt Code:
    1. \mainwindow.cpp:7: error: undefined reference to '_imp___ZN15QAbstractSocket16waitForConnectedEi'
    2. \mainwindow.cpp:22: error: undefined reference to `_imp___ZN10QTcpSocketC1EP7QObject'
    3. \mainwindow.cpp:24: error: undefined reference to `_imp___ZN15QAbstractSocket13connectToHostERK7QStringt6QFlagsIN9QIODevice12OpenModeFlagEE'
    4. \mainwindow.cpp:24: error: undefined reference to `_imp___ZN15QAbstractSocket13connectToHostERK7QStringt6QFlagsIN9QIODevice12OpenModeFlagEE'
    5. \mainwindow.cpp:24: error: undefined reference to `_imp___ZN15QAbstractSocket13connectToHostERK7QStringt6QFlagsIN9QIODevice12OpenModeFlagEE'
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    Is this related with header? And what about rest of code. Is he correct? Maybe i missing somethink?

  4. #4
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    Default Re: Using QTcpSocket to receive binary data

    Post your complete code (mainwindow.cpp & mainwindow.h) to be sure and have some advice, it seems to me you are missing
    Qt Code:
    1. #include <QTcpSocket>
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    or maybe
    Qt Code:
    1. QT += network
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    in your .pro, but without any reproductible code to try can't be too sure.


    For your code, I don't understand why you are testing the connection's state in the slot connected to the readyRead() signal . If you want to be sure you are trully connected used waitForConnected() member or the connected() signal

  5. #5
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    Default Re: Using QTcpSocket to receive binary data

    Quote Originally Posted by nix View Post
    Qt Code:
    1. QT += network
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    Yes. It was it.
    I change my code.
    .cpp
    Qt Code:
    1. #include "mainwindow.h"
    2. #include "ui_mainwindow.h"
    3. #include <QTcpSocket>
    4.  
    5.  
    6. MainWindow::MainWindow(QWidget *parent) :
    7. QMainWindow(parent),
    8. ui(new Ui::MainWindow)
    9. {
    10. ui->setupUi(this);
    11. text = new QLabel("",this);
    12. text->setText("");
    13. text->setGeometry(20,20,400,150);
    14. Test();
    15. }
    16.  
    17. void MainWindow::Test()
    18. {
    19. socket = new QTcpSocket(this);
    20.  
    21. connect(socket,SIGNAL(connected()),this,SLOT(connected()));
    22. connect(socket,SIGNAL(readyRead()),this,SLOT(readyRead()));
    23. //connect(socket,SIGNAL(disconnected()),this,SLOT(disconnected()));
    24.  
    25. text->setText("Conecting...");
    26.  
    27. socket->connectToHost("169.254.19.60",23);
    28. if (!socket->waitForConnected(5000))
    29. {
    30. text->setText("Error: "+socket->errorString());
    31. }
    32. }
    33.  
    34. void MainWindow::connected()
    35. {
    36. text->setText("Connected");
    37. }
    38.  
    39. void MainWindow::readyRead()
    40. {
    41. QByteArray buf = socket->readAll();
    42. text->setText("Reading...\n"+buf);
    43. }
    44.  
    45. //void MainWindow::disconnected()
    46. //{
    47. // text->setText("Disconnected");
    48. //}
    49.  
    50. MainWindow::~MainWindow()
    51. {
    52. delete ui;
    53. }
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    .h
    Qt Code:
    1. #ifndef MAINWINDOW_H
    2. #define MAINWINDOW_H
    3.  
    4. #include <QMainWindow>
    5. #include <QTcpSocket>
    6. #include <QLabel>
    7.  
    8.  
    9. namespace Ui {
    10. class MainWindow;
    11. }
    12.  
    13. class MainWindow : public QMainWindow
    14. {
    15. Q_OBJECT
    16.  
    17. public:
    18. explicit MainWindow(QWidget *parent = 0);
    19. ~MainWindow();
    20.  
    21. void Test();
    22.  
    23. private:
    24. Ui::MainWindow *ui;
    25.  
    26. QTcpSocket *socket;
    27. QLabel *text;
    28.  
    29. public slots:
    30. void connected();
    31. // void disconnected();
    32. void readyRead();
    33. };
    34.  
    35. #endif // MAINWINDOW_H
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    Now i'm getting error with timed out because i don't connect anything to HostAddress in connectToHost but i'm wondering if i connect to my PC microcontroller and send data from it to PC via ethernet will i get data i was send? I want to ask is my code correct to receive binary data? May i send to myself some data and read it using my program (if yes what to add, i try
    Qt Code:
    1. QByteArray writeBuf = "...Data...";
    2. socket->write(writeBuf);
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    but it don't working)? Thanks in advance.

  6. #6
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    Default Re: Using QTcpSocket to receive binary data

    If you want to test your code in local (using only your computer) you have to do your own TCP server based on (QTcpServer) take a look to Fortune server example.

    In your case the first thing you have to do is connecting. Without a connection you can't do anything in TCP socket. A socket is a bidirectionnal channel for communication data you wrote is send on the other side and data wrote by the other side is received by your app, that the basis.
    So it's perfectly normal that you do not received what you sent.

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