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    Unsolved Reading a file with Qt

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    • E
      EL-jos last edited by

      Hello everyone

      as the title indicates, I'm looking to read an entire file with Qt.

      when I read a small size file it is not a problem but when I try to read for example a large size file that there is a problem, my problem is that the package(QByteArray) is not displayed in the console(so it is always empty), here is my code:

      #include <QApplication>
      #include <QFileDialog>
      #include <QFile>
      #include <QDebug>
       
      int main(int argc,char** argv)
      {
          QApplication app(argc,argv);
       
          // Path to the target file to copy
          QString chemin = QFileDialog::getOpenFileName(nullptr,"Path to the file");
       
          // We have our file that we pass as a parameter the path to our target file
          qDebug() << chemin;
          QFile fichier(chemin);
       
          fichier.open(QIODevice::ReadOnly);
          if(fichier.isOpen()){
       
              qDebug() << "File opened and here is the name: " << fichier.fileName();
       
              QFileInfo info(fichier);
              QString extension = info.suffix();
       
              QByteArray paquet;
       
              while(!fichier.atEnd()){
       
                  paquet = fichier.readAll();// full reading of our byte file
              }
       
              if(!paquet.isEmpty()){
       
                 qDebug() << "The data has been well serialized in the byte packet.";
                 qDebug() << paquet;
              }
          }
          return app.exec();
      }
      

      Note: I will read an.txt file of 3.0MB knowing that it is a file that contains genre words from a dictionary.

      in fact if I Serialize and deserialize my dictionary it is because I have to send it into a network,

      so the serialization will be during sending to the network and the de-serialization will be at the destination.

      Thanks in advance for your help.

      1 Reply Last reply Reply Quote 0
      • mrjj
        mrjj Lifetime Qt Champion last edited by mrjj

        Hi
        Tried you code directly
        with
        https://norvig.com/big.txt
        which is 6MB file
        and it just read it in.

        "E:/big.txt"
        File opened and here is the name: "E:/big.txt"
        The data has been well serialized in the byte packet. 6488666

        so are u sure your text file is just 3 MB ?

        1 Reply Last reply Reply Quote 4
        • E
          EL-jos last edited by EL-jos

          @mrjj said in Reading a file with Qt:

          Hi
          Tried you code directly
          with
          https://norvig.com/big.txt
          which is 6MB file
          and it just read it in.
          "E:/big.txt"
          File opened and here is the name: "E:/big.txt"
          The data has been well serialized in the byte packet. 6488666
          so are u sure your text file is just 3 MB ?

          Of course, yes, just 3MB.

          then your result has an error because the package must display all the contents of the file in the console but at home your result is :
          The data has been well serialized in the byte packet. 6488666

          1 Reply Last reply Reply Quote 0
          • SamurayH
            SamurayH last edited by

            Hi @EL-jos,
            Be sure that your paquet contains the file's content, the problem could be with qDebug or the QtCreator's console.If you want to check that out you can use qlabel or qtextBrowser (it will consume some cpu for larger files), or QByteArray::mid.

            QLabel *label = new QLabel(paquet);
            label->showMaximized();
            //--------------------------
            qDebug() << paquet.mid(0,100);
            

            I don't know if it's a length limitation by qDebug, but I don't think so since it isn't mentioned in the documentation.
            You're not the first one, check out that thread to, I took the second line of code from it.

            "قال رسول الله صلى الله عليه وسلم : " أحب الناس إلى الله أنفعهم للناس

            1 Reply Last reply Reply Quote 0
            • M
              mchinand last edited by

              What is the size of paquet after you have read from your file? Does it match the size of the file in bytes? qDebug() has a limited buffer that is probably the issue in this case. Is there other processing of this data that you do after reading it in? Does that still work? Also, if you are reading in a text file, you might want to use QTextStream instead of QByteArray.

              1 Reply Last reply Reply Quote 0
              • Christian Ehrlicher
                Christian Ehrlicher Lifetime Qt Champion last edited by

                @EL-jos said in Reading a file with Qt:

                    while(!fichier.atEnd()){
                
                        paquet = fichier.readAll();// full reading of our byte file
                    }
                

                When here readAll() does not return the complete content with the first call, you will not read all... you want paquet += ...

                Qt has to stay free or it will die.

                1 Reply Last reply Reply Quote 5
                • E
                  EL-jos last edited by

                  Thanks for your help because I just noticed that my file was serialized in the QByteArray except the console could not display it in its entirety because of its buffer.

                  But there is a new problem: when I try to send my QByteArray that contains my serialize file, when the QByteArray arrives at the server it loses all its data so its bytes.

                  Please how to fix this problem?
                  Knowing that I use the TCP protocol.

                  JonB 1 Reply Last reply Reply Quote 0
                  • JonB
                    JonB @EL-jos last edited by

                    @EL-jos
                    From the information you've supplied on the new problem, I would guess some code is wrong somewhere.

                    1 Reply Last reply Reply Quote 0
                    • E
                      EL-jos last edited by

                      Here's my code on the client side:

                      void Controleur::on_pushButton_clicked()
                      {
                          QString chemin = QFileDialog::getOpenFileName(this,"Chemin du fichier");
                          cheminFichier->setText(chemin);
                      
                          QFile fichier(chemin);
                          QFileInfo info(fichier);
                          QString extension = info.suffix();
                      
                          if(fichier.exists()){
                      
                             qDebug() <<"LE fichier existe bel est bienet et voici son extension: " << extension;
                      
                             int reponse = QMessageBox::question(this,"Confirmation d'envie du fichier", "êtes-vous sûr d'<strong>envoyer</strong> le fichier: " + fichier.fileName(), QMessageBox::Yes | QMessageBox::No);
                             if(reponse == QMessageBox::Yes){
                      
                                 qDebug("Donc vous souhaitez envoyer le fichier dans le réseau.");
                      
                                 fichier.open(QIODevice::ReadOnly);
                                 if(fichier.isOpen()){
                      
                                     qDebug() << "Fichier ouvert et voici le nom: " << fichier.fileName();
                      
                                     QByteArray paquetFichier;
                      
                                     while(!fichier.atEnd()){
                      
                                         paquetFichier = fichier.readAll();// lecture entier de notre fichier en octet
                                     }
                      
                                     fichier.close();
                      
                                     if(!paquetFichier.isEmpty()){
                      
                                        qDebug() << "Les données ont été bien sérialiser dans le paquet en octets.";
                                        qDebug() << paquetFichier;
                                     }
                      
                      
                                     QByteArray paquetEnvoieFichier;
                                     QDataStream outFichier(&paquetEnvoieFichier,QIODevice::WriteOnly);
                      
                                     outFichier << (quint16) 0;
                                     outFichier << (quint16) 6;
                                     outFichier << extension;
                                     outFichier << paquetFichier;
                                     outFichier.device()->seek(0);
                                     outFichier << (quint16) (paquetEnvoieFichier.size() - sizeof(quint16));
                                     m_client->getSocket()->write(paquetEnvoieFichier);
                                 }// Fin fichier isOpen
                                } // Fin MessageBox::YES
                             } // Fin si le fichier existe
                      }
                      
                      

                      and this is the one for reading

                      if(id == (quint16) 6){
                      
                              qDebug() << "réception d'un fichier venant du serveur.";
                      
                              QString extension;
                              QByteArray  paquetReception;
                      
                              in >> extension;
                              in >> paquetReception;
                      
                              qDebug() << "voici l'extension du fichier: " << extension <<" le paquet est: " <<paquetReception;
                      
                              QFile fichier("AutreFichier."+ extension);
                              fichier.open(QIODevice::WriteOnly);
                      
                              if(fichier.isOpen()){
                      
                                  qDebug("Le fichier de la copie se -t- ouvert en écriture seul.");
                                  qDebug() << "avec l'extension: " + extension;
                      
                                  QDataStream outAutreFichier(&fichier);
                                  outAutreFichier << paquetReception;
                              }
                      
                      1 Reply Last reply Reply Quote 0
                      • Christian Ehrlicher
                        Christian Ehrlicher Lifetime Qt Champion last edited by

                        My comment is still not fixed... and now - what do you think will happen when your file size is greater than 65535 bytes?

                        outFichier << (quint16) (paquetEnvoieFichier.size() - sizeof(quint16));
                        And then you don't write the data directly to a file but stream it as QDataStream - this will add some more information in the front which is definitly not what you want... use
                        QFile::write(QByteArray())

                        And when sending data via network, readyRead() will for sure not contain the whole content - at least not when you're sending 6MB. Please take a look at the QTcpServer/Client examples (and avoid using QDataStream here - it's not needed at all...)

                        Qt has to stay free or it will die.

                        1 Reply Last reply Reply Quote 2
                        • E
                          EL-jos last edited by

                          Yes I have this problem because I noticed that if my file size is larger than 65535 bytes, the server does not receive all the information. But how do we solve this problem?

                          Then if I use Qdatastream this to first write the identifier of my message because the one that says if it is a text message (5), if it is a new connection (3), if it is a disconnect (4) and for the file the identifier value is (7) to tell the server that it is a file. Here the QDATASTREAM allows me to write a screen like this:

                          *Message size

                          *Identifier

                          *Message

                          So if I don't use a Qdatastream how can I write in my QByteArray?

                          Translated with www.DeepL.com/Translator

                          aha_1980 1 Reply Last reply Reply Quote 0
                          • aha_1980
                            aha_1980 Lifetime Qt Champion @EL-jos last edited by

                            Hi @EL-jos,

                            What do you want to do exactly?

                            For file transfer, decicated protocols exists, e.g. FTP or HTTP. To me it looks like your are re-inventing the wheel?

                            Regards

                            Qt has to stay free or it will die.

                            1 Reply Last reply Reply Quote 0
                            • E
                              EL-jos last edited by EL-jos

                              Concretely I want my client to send a file to my server and the server after receiving the file, that it sends this file to all the client that are connected to it.
                              Because it is a chat software then I also want the client to be able to send a file to another client via a server.

                              1 Reply Last reply Reply Quote 0
                              • Christian Ehrlicher
                                Christian Ehrlicher Lifetime Qt Champion last edited by

                                Please take a look at the examples (again...) how to send large data ... http://doc.qt.io/qt-5/qtnetwork-loopback-example.html

                                Qt has to stay free or it will die.

                                1 Reply Last reply Reply Quote 2
                                • E
                                  EL-jos last edited by

                                  Okay Thanks, I'll read this example and then I'll come back to you to give you the follow-up.

                                  Thank you

                                  1 Reply Last reply Reply Quote 0
                                  • E
                                    EL-jos last edited by

                                    Hi,
                                    after several studies of the example given by the Qt documentation, I don't know where and how to send my file to the server?

                                    then in the example given by the Qt documentation, just sends the same 64KB packet several times until it tints 50MB . and the server and the client are in the same project but in my case the client and the server are different projects

                                    1 Reply Last reply Reply Quote 0
                                    • SGaist
                                      SGaist Lifetime Qt Champion last edited by

                                      Hi,

                                      Are you writing both the client and server parts ?

                                      Interested in AI ? www.idiap.ch
                                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                      1 Reply Last reply Reply Quote 0
                                      • E
                                        EL-jos last edited by

                                        Yes, do you want me to mail them?

                                        1 Reply Last reply Reply Quote 0
                                        • SGaist
                                          SGaist Lifetime Qt Champion last edited by

                                          It was regarding your last remark about the server and client being in the same project. Since you are writing both, then it doesn't matter that they are in different projects.

                                          Interested in AI ? www.idiap.ch
                                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                          1 Reply Last reply Reply Quote 1
                                          • E
                                            EL-jos last edited by

                                            Hey, everybody,

                                            Still in the example given by the Qt documentation for the exchange of large documents between the client and the server in a chatt software, I could separate the client and the server in different projects which is not the case in the example given by the Qt documentation.

                                            So here's my question:

                                            Just that there I do not know how to adapt this example to my chatt software to be able to send large files between client and server?

                                            Translated with www.DeepL.com/Translator

                                            1 Reply Last reply Reply Quote 0
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