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Use Json data in Qt in Windows

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  • Negar_mgN Negar_mg

    @JonB
    Thanks , can I use QJsonDocument Class to read json from serial port?
    Is it possible to read and write this data in qt or c ++ libraries?

    JonBJ Offline
    JonBJ Offline
    JonB
    wrote on last edited by
    #8

    @Negar_mg
    As you can read at https://doc.qt.io/qt-5/qjsondocument.html#details

    QJsonDocument is a class that wraps a complete JSON document and can read and write this document both from a UTF-8 encoded text based representation as well as Qt's own binary format.

    Since you will use QJsonDocument QJsonDocument::fromJson(const QByteArray &json, QJsonParseError *error = nullptr) you will need a QByteArray. It does not do the reading, you will need to fetch the bytes from the serial port.

    Is it possible to read and write this data in qt or c ++ libraries?

    Read and write what data? Serial port? Yes. JSON? Yes.

    Negar_mgN 1 Reply Last reply
    2
    • JonBJ JonB

      @Negar_mg
      As you can read at https://doc.qt.io/qt-5/qjsondocument.html#details

      QJsonDocument is a class that wraps a complete JSON document and can read and write this document both from a UTF-8 encoded text based representation as well as Qt's own binary format.

      Since you will use QJsonDocument QJsonDocument::fromJson(const QByteArray &json, QJsonParseError *error = nullptr) you will need a QByteArray. It does not do the reading, you will need to fetch the bytes from the serial port.

      Is it possible to read and write this data in qt or c ++ libraries?

      Read and write what data? Serial port? Yes. JSON? Yes.

      Negar_mgN Offline
      Negar_mgN Offline
      Negar_mg
      wrote on last edited by Negar_mg
      #9

      @JonB
      Thanks for the explanation. I'm trying it now
      I just had one more question, should I use QSerialPort Class to fetch Json data from the serial port?

      JonBJ 1 Reply Last reply
      0
      • Negar_mgN Negar_mg

        @JonB
        Thanks for the explanation. I'm trying it now
        I just had one more question, should I use QSerialPort Class to fetch Json data from the serial port?

        JonBJ Offline
        JonBJ Offline
        JonB
        wrote on last edited by
        #10

        @Negar_mg
        Yes that's fine. Try to separate serial data and JSON data in your head. Serial data is just bytes, it could be anything. JSON is treat bytes as text and parse it as JSON. Two unconnected things, you can put them together if it suits you.

        Negar_mgN 1 Reply Last reply
        1
        • JonBJ JonB

          @Negar_mg
          Yes that's fine. Try to separate serial data and JSON data in your head. Serial data is just bytes, it could be anything. JSON is treat bytes as text and parse it as JSON. Two unconnected things, you can put them together if it suits you.

          Negar_mgN Offline
          Negar_mgN Offline
          Negar_mg
          wrote on last edited by
          #11

          @JonB
          thanks alot

          1 Reply Last reply
          0
          • Negar_mgN Offline
            Negar_mgN Offline
            Negar_mg
            wrote on last edited by
            #12

            I used the following code and was able to get Json data from the serial port.
            But the data is displayed as I sent it to you in the image, how can I separate it and store each in a different variable?

               serial.setPortName("COM3");
               serial.open(QIODevice::ReadWrite);
               serial.setBaudRate(QSerialPort::Baud9600);
               serial.setDataBits(QSerialPort::Data8);
               serial.setParity(QSerialPort::NoParity);
               serial.setStopBits(QSerialPort::OneStop);
               serial.setFlowControl(QSerialPort::NoFlowControl);
                while(!serial.isOpen()) serial.open(QIODevice::ReadWrite);
            
               if (serial.isOpen() && serial.isWritable())
               {
               qDebug() << "Serial is open";
            
               QByteArray output;
               QByteArray input;
            
                 while(true)
                 {
                 output = "a";
                 serial.write(output);
                serial.flush();
            
                 serial.waitForBytesWritten(1000);
                 serial.waitForReadyRead(1000);
            
                 input = serial.readAll();
                 qDebug()<<input;
            
            
                 }
            
            
               }
            

            2.png

            The data should be as follows, but as you can see in the first image, the data is not readable
            1.png

            1 Reply Last reply
            0
            • Christian EhrlicherC Offline
              Christian EhrlicherC Offline
              Christian Ehrlicher
              Lifetime Qt Champion
              wrote on last edited by
              #13

              I don't see a difference between those two pictures. The json content is exactly the same. If you want to parse the json you should take a look at the documentation of QJsonDocument and it's corresponding classes.

              Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
              Visit the Qt Academy at https://academy.qt.io/catalog

              Negar_mgN 1 Reply Last reply
              0
              • Christian EhrlicherC Christian Ehrlicher

                I don't see a difference between those two pictures. The json content is exactly the same. If you want to parse the json you should take a look at the documentation of QJsonDocument and it's corresponding classes.

                Negar_mgN Offline
                Negar_mgN Offline
                Negar_mg
                wrote on last edited by
                #14

                @Christian-Ehrlicher
                Thanks, how can I separate the data? I do not know how to use QJsonDocument?
                Can you guide me with an example? For example, what should I do to store the amount of Bat_Temp data in the x variable?

                mrjjM 1 Reply Last reply
                0
                • Negar_mgN Negar_mg

                  @Christian-Ehrlicher
                  Thanks, how can I separate the data? I do not know how to use QJsonDocument?
                  Can you guide me with an example? For example, what should I do to store the amount of Bat_Temp data in the x variable?

                  mrjjM Offline
                  mrjjM Offline
                  mrjj
                  Lifetime Qt Champion
                  wrote on last edited by mrjj
                  #15

                  @Negar_mg said in Use Json data in Qt in Windows:

                  QJsonDocument

                     QString input = "{Bat_temp:19}"; // you used a picture so could not get real input
                    // the toUTF is due to it wants a bytearrya not qstring. 
                     QJsonDocument jsonResponse = QJsonDocument::fromJson(input.toUtf8());
                    // ask for a json object
                      QJsonObject jsonObject = jsonResponse.object();
                    //access a property of that json object
                      int value = jsonObject["Bat_temp"].toInt();
                  
                  

                  for dht11Data you must use QJsonArray

                  Negar_mgN 1 Reply Last reply
                  1
                  • mrjjM mrjj

                    @Negar_mg said in Use Json data in Qt in Windows:

                    QJsonDocument

                       QString input = "{Bat_temp:19}"; // you used a picture so could not get real input
                      // the toUTF is due to it wants a bytearrya not qstring. 
                       QJsonDocument jsonResponse = QJsonDocument::fromJson(input.toUtf8());
                      // ask for a json object
                        QJsonObject jsonObject = jsonResponse.object();
                      //access a property of that json object
                        int value = jsonObject["Bat_temp"].toInt();
                    
                    

                    for dht11Data you must use QJsonArray

                    Negar_mgN Offline
                    Negar_mgN Offline
                    Negar_mg
                    wrote on last edited by
                    #16

                    @mrjj
                    thank you

                    1 Reply Last reply
                    0
                    • _ Offline
                      _ Offline
                      _-mohamed-_
                      wrote on last edited by
                      #17

                      @Negar_mg this is the best example, it helped me a lot:
                      Example of how to use JSON file with QT

                      Negar_mgN 1 Reply Last reply
                      0
                      • _ _-mohamed-_

                        @Negar_mg this is the best example, it helped me a lot:
                        Example of how to use JSON file with QT

                        Negar_mgN Offline
                        Negar_mgN Offline
                        Negar_mg
                        wrote on last edited by
                        #18

                        @_-mohamed-_
                        thanks a lot
                        You know, my problem is that I receive data from the Arduino from the serial port
                        As I wrote in the above code, I can print data with an infinite loop.
                        As follows :

                                    while (true)
                                    {
                                    serial.waitForReadyRead (100000);
                                    input = input.append (serial.readAll ());
                                    qDebug () << input;
                                    }
                        

                        And the output is as follows:

                        //..............................................................................................................................
                        Serial is open
                        "{"
                        "{" dht "
                        "{" dht11Da "
                        "{" dht11Data \ ":"
                        "{" dht11Data \ ": [29,"
                        "{" dht11Data \ ": [29,27]}"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " "
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht1 "
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Da "
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ":"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n]"
                        "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n] \ r \ n } "
                        //..........................................................................................................................................
                        No data is received at first, so I do not know how to manage this infinite loop and store the data in an array

                        _ jsulmJ 2 Replies Last reply
                        0
                        • Negar_mgN Negar_mg

                          @_-mohamed-_
                          thanks a lot
                          You know, my problem is that I receive data from the Arduino from the serial port
                          As I wrote in the above code, I can print data with an infinite loop.
                          As follows :

                                      while (true)
                                      {
                                      serial.waitForReadyRead (100000);
                                      input = input.append (serial.readAll ());
                                      qDebug () << input;
                                      }
                          

                          And the output is as follows:

                          //..............................................................................................................................
                          Serial is open
                          "{"
                          "{" dht "
                          "{" dht11Da "
                          "{" dht11Data \ ":"
                          "{" dht11Data \ ": [29,"
                          "{" dht11Data \ ": [29,27]}"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " "
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht1 "
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Da "
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ":"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n]"
                          "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n] \ r \ n } "
                          //..........................................................................................................................................
                          No data is received at first, so I do not know how to manage this infinite loop and store the data in an array

                          _ Offline
                          _ Offline
                          _-mohamed-_
                          wrote on last edited by
                          #19

                          @Negar_mg do you mean that you want to save the final result in a json file?

                          Negar_mgN 1 Reply Last reply
                          0
                          • _ _-mohamed-_

                            @Negar_mg do you mean that you want to save the final result in a json file?

                            Negar_mgN Offline
                            Negar_mgN Offline
                            Negar_mg
                            wrote on last edited by
                            #20

                            @_-mohamed-_
                            i want to save this {" dht11Data \ ": [29,27]}
                            And I want to display each of the numbers like 27 in one lineEdit.

                            _ 1 Reply Last reply
                            0
                            • Negar_mgN Negar_mg

                              @_-mohamed-_
                              i want to save this {" dht11Data \ ": [29,27]}
                              And I want to display each of the numbers like 27 in one lineEdit.

                              _ Offline
                              _ Offline
                              _-mohamed-_
                              wrote on last edited by
                              #21

                              @Negar_mg You can't use a backslash in the key, you can use FrontSlash instead

                              This is the code you need:

                              #include <QApplication>
                              #include <QJsonDocument>
                              #include <QJsonObject>
                              #include <QJsonArray>
                              #include <QByteArray>
                              #include <QJsonValue>
                              #include <QDebug>
                              #include <QFile>
                              
                              int main(int argc, char *argv[])
                              {
                                  QApplication a(argc, argv);
                              
                                  QFile file("C:/Users/moham/OneDrive/Desktop/json file.json"); //write the file path here
                              
                                  if(!file.open(QFile::ReadOnly))    //opening file
                                      qDebug() << "can't open the file";
                              
                                  else
                                  {
                                      QByteArray fileContents = file.readAll(); // reading the file
                                      file.close();   //closing file
                              
                                      QJsonDocument jsonDoc = QJsonDocument::fromJson(fileContents);
                              
                                      QJsonObject jsonObj = jsonDoc.object();
                              
                                      QJsonArray jsonArray = jsonObj[" dht11Data / "].toArray();
                              
                                      foreach(QJsonValue v, jsonArray)  //printing array's values
                                          qDebug() << v.toInt();        //
                              
                                      return 0;
                                  }
                              
                                  return a.exec();
                              }
                              

                              this code reads (JSON file.json) and prints it in the console, you can use the values wherever you want.

                              I hope I helped you.

                              1 Reply Last reply
                              1
                              • Negar_mgN Negar_mg

                                @_-mohamed-_
                                thanks a lot
                                You know, my problem is that I receive data from the Arduino from the serial port
                                As I wrote in the above code, I can print data with an infinite loop.
                                As follows :

                                            while (true)
                                            {
                                            serial.waitForReadyRead (100000);
                                            input = input.append (serial.readAll ());
                                            qDebug () << input;
                                            }
                                

                                And the output is as follows:

                                //..............................................................................................................................
                                Serial is open
                                "{"
                                "{" dht "
                                "{" dht11Da "
                                "{" dht11Data \ ":"
                                "{" dht11Data \ ": [29,"
                                "{" dht11Data \ ": [29,27]}"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " "
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht1 "
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Da "
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ":"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n]"
                                "{" dht11Data \ ": [29,27]} \ r \ n {\ r \ n " dht11Data \ ": [\ r \ n 29, \ r \ n 27 \ r \ n] \ r \ n } "
                                //..........................................................................................................................................
                                No data is received at first, so I do not know how to manage this infinite loop and store the data in an array

                                jsulmJ Offline
                                jsulmJ Offline
                                jsulm
                                Lifetime Qt Champion
                                wrote on last edited by
                                #22

                                @Negar_mg said in Use Json data in Qt in Windows:

                                infinite loop

                                Stop using infinite loops first!
                                Please take a look at documentation and examples to see how to properly use QSerialPort: https://doc.qt.io/qt-5/qtserialport-creaderasync-example.html
                                To read from serial port connect a slot to https://doc.qt.io/qt-5/qiodevice.html#readyRead signal and use readAll() in this slot. Keep in mind that you have to accumulate the data read from serial port until you got whole JSON document!

                                https://forum.qt.io/topic/113070/qt-code-of-conduct

                                1 Reply Last reply
                                4
                                • Negar_mgN Offline
                                  Negar_mgN Offline
                                  Negar_mg
                                  wrote on last edited by
                                  #23

                                  Thank you all

                                  1 Reply Last reply
                                  0
                                  • Negar_mgN Offline
                                    Negar_mgN Offline
                                    Negar_mg
                                    wrote on last edited by Negar_mg
                                    #24

                                    I finally succeeded,The code I wrote is as follows:

                                     MainWindow::MainWindow(QWidget *parent)
                                    : QMainWindow(parent)
                                    , ui(new Ui::MainWindow)
                                      {
                                    ui->setupUi(this);
                                    
                                       m_serialPort=new QSerialPort;
                                       m_serialPort->setPortName("COM3");
                                    
                                       m_serialPort->open(QIODevice::ReadWrite);
                                       m_serialPort->setBaudRate(QSerialPort::Baud9600);
                                       m_serialPort->setDataBits(QSerialPort::Data8);
                                       m_serialPort->setParity(QSerialPort::NoParity);
                                       m_serialPort->setStopBits(QSerialPort::OneStop);
                                       m_serialPort->setFlowControl(QSerialPort::NoFlowControl);
                                        while(!m_serialPort->isOpen()) m_serialPort->open(QIODevice::ReadWrite);
                                    
                                        connect(m_serialPort, &QSerialPort::readyRead, this, &MainWindow::handleReadyRead);
                                        connect(&m_timer, &QTimer::timeout, this, &MainWindow::handleTimeout);
                                    
                                        m_timer.start(5000);
                                     }
                                    
                                    
                                           void MainWindow::handleReadyRead()
                                          {
                                       m_readData.append(m_serialPort->readAll());
                                    
                                    if (!m_timer.isActive())
                                        m_timer.start(5000);
                                      }
                                    
                                        void MainWindow::handleTimeout()
                                     {
                                    if (m_readData.isEmpty()) {
                                        qDebug()<< "m_readData is empty" <<m_readData;
                                    
                                    } else {
                                    
                                    
                                        qDebug()<< "m_readData is full" <<m_readData;
                                    
                                    
                                    
                                    
                                        QJsonDocument jsonDoc = QJsonDocument::fromJson(m_readData);
                                        QJsonObject jsonObj = jsonDoc.object();
                                    
                                        QJsonValue jsonVal;
                                        jsonVal = jsonObj.value(QString("Bat_Temp"));
                                        QTextStream textStream(stdout);
                                        textStream << QString::number(jsonVal.toInt()) << endl;
                                    }
                                    
                                    1 Reply Last reply
                                    2

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