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How to get first element of QList

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  • JKSHJ JKSH

    @suslucoder said in How to get first element of QList:

    How can i get the first element of my list

    https://doc.qt.io/qt-5/qlist.html#first

    which name is index

    This name will cause lots of confusion. The word "index" means "a position in a list". Why would you call your list "index"? Please give it a non-ambiguous name.

    I've tried to index.at() but it doesnt work.

    What do you mean by "it doesn't work"? Show your code. Show the output of your code. Show us what you expected the output to be.

    Index have 14, 0 ,1 ,13 respectively.

    I don't understand what you mean.

                           QList<int> index;
                           index << inner_data[1].toString().toInt();
    

    After this code runs, your list will contain only 1 integer.

                                  qDebug() << index;
    

    This code prints your whole list.

    D Offline
    D Offline
    deleted286
    wrote on last edited by deleted286
    #3

    @JKSH

     QList<int> list;
       list << inner_data[1].toString().toInt();
         qDebug() << list;
    

    when i run this output is

    (14)
    (0)
    (1)
    (13)
    

    when i run this:

    qDebug() << list.at(0);
    

    output is

    14
    0
    1
    13
    

    I want to achieve them seperately
    I expect that when i run list.at(0) it gives me 14

    JKSHJ 1 Reply Last reply
    0
    • D deleted286

      @JKSH

       QList<int> list;
         list << inner_data[1].toString().toInt();
           qDebug() << list;
      

      when i run this output is

      (14)
      (0)
      (1)
      (13)
      

      when i run this:

      qDebug() << list.at(0);
      

      output is

      14
      0
      1
      13
      

      I want to achieve them seperately
      I expect that when i run list.at(0) it gives me 14

      JKSHJ Offline
      JKSHJ Offline
      JKSH
      Moderators
      wrote on last edited by
      #4

      @suslucoder said in How to get first element of QList:

       QList<int> list;
         list << inner_data[1].toString().toInt();
           qDebug() << list;
      

      when i run this output is

      (14)
      (0)
      (1)
      (13)
      

      You must be running that code in a loop. Do you know that you called qDebug() 4 times?

      Every loop iteration, you put 1 item in the list and then destroy the list.

      Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

      D 1 Reply Last reply
      1
      • JKSHJ JKSH

        @suslucoder said in How to get first element of QList:

         QList<int> list;
           list << inner_data[1].toString().toInt();
             qDebug() << list;
        

        when i run this output is

        (14)
        (0)
        (1)
        (13)
        

        You must be running that code in a loop. Do you know that you called qDebug() 4 times?

        Every loop iteration, you put 1 item in the list and then destroy the list.

        D Offline
        D Offline
        deleted286
        wrote on last edited by
        #5

        @JKSH if you can look at my last question, the complete code is there. My mind so confused

        JKSHJ 1 Reply Last reply
        0
        • D deleted286

          @JKSH if you can look at my last question, the complete code is there. My mind so confused

          JKSHJ Offline
          JKSHJ Offline
          JKSH
          Moderators
          wrote on last edited by JKSH
          #6

          @suslucoder said in How to get first element of QList:

          @JKSH if you can look at my last question, the complete code is there. My mind so confused

          You need to learn how to use loops.

          Add more debug messages to your code; it might help you see what's happening:

          qDebug() << "I am creating an empty list now.";
          
          QList<int> list;
          
          qDebug() << "My list contains" << list.count() << "items.";
          qDebug() << "My whole list is" << list;
          
          qDebug() << "I am putting an integer into my list now.";
          
          list << inner_data[1].toString().toInt();
          
          qDebug() << "My list contains" << list.count() << "items.";
          qDebug() << "My whole list is" << list;
          

          Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

          D 1 Reply Last reply
          1
          • JKSHJ JKSH

            @suslucoder said in How to get first element of QList:

            @JKSH if you can look at my last question, the complete code is there. My mind so confused

            You need to learn how to use loops.

            Add more debug messages to your code; it might help you see what's happening:

            qDebug() << "I am creating an empty list now.";
            
            QList<int> list;
            
            qDebug() << "My list contains" << list.count() << "items.";
            qDebug() << "My whole list is" << list;
            
            qDebug() << "I am putting an integer into my list now.";
            
            list << inner_data[1].toString().toInt();
            
            qDebug() << "My list contains" << list.count() << "items.";
            qDebug() << "My whole list is" << list;
            
            D Offline
            D Offline
            deleted286
            wrote on last edited by
            #7

            @JKSH Thank you but i didnt understand still how can i get items seperately

            JKSHJ 1 Reply Last reply
            0
            • D deleted286

              @JKSH Thank you but i didnt understand still how can i get items seperately

              JKSHJ Offline
              JKSHJ Offline
              JKSH
              Moderators
              wrote on last edited by
              #8

              @suslucoder Did you run the code that I posted? What did you discover?

              Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

              D 1 Reply Last reply
              0
              • JKSHJ JKSH

                @suslucoder Did you run the code that I posted? What did you discover?

                D Offline
                D Offline
                deleted286
                wrote on last edited by
                #9

                @JKSH Yes i run it. I realize that, it add the elements into list by one by.
                I move to the definition of list to my header.

                run this

                                     list << inner_data[1].toString().toInt();
                                     qDebug() << "My list contains" << list.count() << "items.";
                                     qDebug() << "My whole list is" << list;
                

                and achieve this, by i didnt solve why

                My list contains 1 items.
                My whole list is (14)
                My list contains 2 items.
                My whole list is (14, 0)
                My list contains 3 items.
                My whole list is (14, 0, 1)
                My list contains 4 items.
                My whole list is (14, 0, 1, 13)
                
                JKSHJ 1 Reply Last reply
                1
                • D deleted286

                  @JKSH Yes i run it. I realize that, it add the elements into list by one by.
                  I move to the definition of list to my header.

                  run this

                                       list << inner_data[1].toString().toInt();
                                       qDebug() << "My list contains" << list.count() << "items.";
                                       qDebug() << "My whole list is" << list;
                  

                  and achieve this, by i didnt solve why

                  My list contains 1 items.
                  My whole list is (14)
                  My list contains 2 items.
                  My whole list is (14, 0)
                  My list contains 3 items.
                  My whole list is (14, 0, 1)
                  My list contains 4 items.
                  My whole list is (14, 0, 1, 13)
                  
                  JKSHJ Offline
                  JKSHJ Offline
                  JKSH
                  Moderators
                  wrote on last edited by
                  #10

                  @suslucoder said in How to get first element of QList:

                  and achieve this

                  Good job. Now try list.at(0) again.

                  Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                  D 1 Reply Last reply
                  0
                  • JKSHJ JKSH

                    @suslucoder said in How to get first element of QList:

                    and achieve this

                    Good job. Now try list.at(0) again.

                    D Offline
                    D Offline
                    deleted286
                    wrote on last edited by deleted286
                    #11

                    @JKSH it gives me the first item but 4 times.

                    Why? I didnt understand this. Becauuse if my inner_data[1] size is 4?
                    How can i solve it?

                    I expect that giving just this

                    My list contains 4 items.
                    My whole list is (14, 0, 1, 13)
                    
                    J.HilkJ JKSHJ 2 Replies Last reply
                    0
                    • D deleted286

                      @JKSH it gives me the first item but 4 times.

                      Why? I didnt understand this. Becauuse if my inner_data[1] size is 4?
                      How can i solve it?

                      I expect that giving just this

                      My list contains 4 items.
                      My whole list is (14, 0, 1, 13)
                      
                      J.HilkJ Offline
                      J.HilkJ Offline
                      J.Hilk
                      Moderators
                      wrote on last edited by
                      #12

                      @suslucoder
                      ok, please post the whole function, from opening { to closing }


                      Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                      Q: What's that?
                      A: It's blue light.
                      Q: What does it do?
                      A: It turns blue.

                      D 1 Reply Last reply
                      0
                      • D deleted286

                        @JKSH it gives me the first item but 4 times.

                        Why? I didnt understand this. Becauuse if my inner_data[1] size is 4?
                        How can i solve it?

                        I expect that giving just this

                        My list contains 4 items.
                        My whole list is (14, 0, 1, 13)
                        
                        JKSHJ Offline
                        JKSHJ Offline
                        JKSH
                        Moderators
                        wrote on last edited by JKSH
                        #13

                        @suslucoder said in How to get first element of QList:

                        @JKSH it gives me the first item but 4 times.

                        Why?

                        Because you called list.at(0) 4 times, in a loop.

                        Loops are used to run code repeatedly. If you don't want a line of code to run repeatedly, then you must put that line outside the loop.

                        How much do you understand for-loops?

                        Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                        1 Reply Last reply
                        1
                        • J.HilkJ J.Hilk

                          @suslucoder
                          ok, please post the whole function, from opening { to closing }

                          D Offline
                          D Offline
                          deleted286
                          wrote on last edited by
                          #14

                          @J-Hilk

                              void MainWindow::Okuma()
                           {
                          
                          QFile file("readJson/deneme.json");
                          
                          
                              file.open(QIODevice::ReadOnly | QIODevice::Text);
                          
                              QByteArray data = file.readAll();
                              QJsonDocument doc = QJsonDocument::fromJson(data);
                          
                              QJsonObject root = doc.object();
                              QJsonArray tlmtArray = root.value("Telemetri Verileri").toArray();
                          
                              for(int i = 0; i < tlmtArray.size(); ++i)
                                 {
                                     QJsonObject obj = tlmtArray[i].toObject();
                                     QJsonArray gps_array = obj.value("GPS").toArray();
                          
                              for(int j = 0; j < gps_array.size(); ++j)
                                  {
                                      QJsonObject gps_obj = gps_array[j].toObject();
                          
                                      for(QJsonObject::const_iterator cit = gps_obj.constBegin(); cit != gps_obj.constEnd(); ++cit)
                                      {
                                         // qDebug() << cit.key().toStdU16String() <<  ": (";
                          
                                          QJsonArray inner_data = cit.value().toArray();
                          
                                              if(inner_data[0] == "float")
                                              {
                                                 // qDebug() << inner_data[0].toString().toStdU16String() << (0 < inner_data.size()-1 ? "," : "");
                          
                          
                                              }
                          
                          
                                           if (inner_data[0] == "integer")
                                              {
                                             //   qDebug() << inner_data[0].toString().toStdU16String() << (0 < inner_data.size()-1 ? "," : "");
                                               list << inner_data[1].toString().toInt();
                          
                               //                         qDebug() << "My list contains" << list.count() << "items.";
                               //                         qDebug() << "My whole list is" << list;
                          
                                               qDebug() << list.at(0);
                                              }
                          
                                      }
                                  }
                          
                              }
                          

                          }

                          1 Reply Last reply
                          0
                          • J.HilkJ Offline
                            J.HilkJ Offline
                            J.Hilk
                            Moderators
                            wrote on last edited by
                            #15

                            @suslucoder ok, list magically appears, so I assume its a class member, the formatting is horrible,but my guess this is most likely to do copy & past issues in the forum.

                            Place your qDebug here, and it should work fine

                            void Okuma ()
                            {
                                
                                QFile file("readJson/deneme.json");
                                
                                
                                file.open(QIODevice::ReadOnly | QIODevice::Text);
                                
                                QByteArray data = file.readAll();
                                QJsonDocument doc = QJsonDocument::fromJson(data);
                                
                                QJsonObject root = doc.object();
                                QJsonArray tlmtArray = root.value("Telemetri Verileri").toArray();
                                
                                for(int i = 0; i < tlmtArray.size(); ++i) {
                                    QJsonObject obj = tlmtArray[i].toObject();
                                    QJsonArray gps_array = obj.value("GPS").toArray();
                                    
                                    for(int j = 0; j < gps_array.size(); ++j) {
                                        QJsonObject gps_obj = gps_array[j].toObject();
                                        
                                        for(QJsonObject::const_iterator cit = gps_obj.constBegin(); cit != gps_obj.constEnd(); ++cit) {
                                            
                                            QJsonArray inner_data = cit.value().toArray();
                                            
                                            if(inner_data[0] == "float") {
                                                // qDebug() << inner_data[0].toString().toStdU16String() << (0 < inner_data.size()-1 ? "," : "");
                            
                                            }
                                            
                                            if (inner_data[0] == "integer") {
                                                //   qDebug() << inner_data[0].toString().toStdU16String() << (0 < inner_data.size()-1 ? "," : "");
                                                list << inner_data[1].toString().toInt();
                                                
                                                //                         qDebug() << "My list contains" << list.count() << "items.";
                                                //                         qDebug() << "My whole list is" << list;
                                                
                                            }
                                        }
                                    }
                                }
                                if(!list.isEmpty())
                                   qDebug() << list.at(0);
                                else
                                  qDebug() << "List has no elements"
                            }
                            

                            Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                            Q: What's that?
                            A: It's blue light.
                            Q: What does it do?
                            A: It turns blue.

                            1 Reply Last reply
                            1
                            • Ketan__Patel__0011K Offline
                              Ketan__Patel__0011K Offline
                              Ketan__Patel__0011
                              wrote on last edited by
                              #16

                              @suslucoder said in How to get first element of QList:

                              QList<int> index;

                              try this way

                                  QList<int> index;
                                  index.push_back(10);
                                  index.push_back(20);
                                  index.push_back(30);
                                  index.push_back(40);
                                  index.push_back(50);
                              
                                  qDebug() << index.at(0); /// Answer Is 10
                              
                              JKSHJ 1 Reply Last reply
                              0
                              • Ketan__Patel__0011K Ketan__Patel__0011

                                @suslucoder said in How to get first element of QList:

                                QList<int> index;

                                try this way

                                    QList<int> index;
                                    index.push_back(10);
                                    index.push_back(20);
                                    index.push_back(30);
                                    index.push_back(40);
                                    index.push_back(50);
                                
                                    qDebug() << index.at(0); /// Answer Is 10
                                
                                JKSHJ Offline
                                JKSHJ Offline
                                JKSH
                                Moderators
                                wrote on last edited by
                                #17

                                @Ketan__Patel__0011 said in How to get first element of QList:

                                try this way

                                    QList<int> index;
                                    index.push_back(10);
                                    index.push_back(20);
                                    index.push_back(30);
                                    index.push_back(40);
                                    index.push_back(50);
                                
                                    qDebug() << index.at(0); /// Answer Is 10
                                

                                OP already figured out the function for obtaining the first element: https://forum.qt.io/post/650999 Their current problem is how to avoid calling it inside a loop.

                                Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                                1 Reply Last reply
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