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Windows not responding on reading file from txt



  • Hi everyone. I have 2 different txt file. One is for writing and the other one is reading. Writing part is working but when I clicked the read button windows not responding. Can somebody help me in that issue? Here is my code:

    #include "mainwindow.h"
    #include "ui_mainwindow.h"
    #include <QFile>
    #include <QTextStream>
    #include <QMessageBox>
    
    
    
    MainWindow::MainWindow(QWidget *parent)
        : QMainWindow(parent)
        , ui(new Ui::MainWindow)
    {
        ui->setupUi(this);
    
       
    
    
    }
    
    MainWindow::~MainWindow()
    {
        delete ui;
    }
    
    
    void MainWindow::on_pushButton_2_clicked()  //write
    {
        QFile file("C:/Users/ilknu/Documents/QFileDemo/abc.txt");
        if(!file.open(QFile::WriteOnly | QFile::Text )) {
    
            QMessageBox::warning(this, "title", "file not open");
    
    
        }
    
        QTextStream out (&file);
        QString text = ui->plainTextEdit->toPlainText();
        out << text;
        file.flush();
        file.close();
    
    
    }
    
    void MainWindow::on_pushButton_clicked()  //read
    {
    
        QFile file("C:/Users/ilknu/Documents/QFileDemo/abc.txt");
    
     
    
        if(!file.open(QFile::ReadOnly | QFile::Text)) {
            QMessageBox::warning(this, "title", "file cannot open");
        }
    
    
        QTextStream stream(&file);
        QString line = stream.readLine();
        while (!line.isNull()) {
            continue;
    
        }
        line = stream.readLine();
        ui -> plainTextEdit->setPlainText(line);
        file.close();
    
    
    }


  • @suslucoder said in Windows not responding on reading file from txt:

    QString line = stream.readLine();
         while (!line.isNull()) {
             continue;
     }
    

    It seems to me you have an endless loop in there...



  • @JohanSolo actually i want to do this --> continue reading until the line is null. How can i fix it?


  • Lifetime Qt Champion

    Hi
    The reason it stops responding is this if sentence

    QString line = stream.readLine();
    while (!line.isNull()) {  <<<  since we just read a line above, it wont ever be be true and loop will loop forever
        continue;
    }
    

    you want logic to look like

    QFile inputFile(fileName);
    if (inputFile.open(QIODevice::ReadOnly))
    {
       QTextStream in(&inputFile);
       while (!in.atEnd())
       {
          QString line = in.readLine();
          ... put line to plainTextEdit
       }
       inputFile.close();
    }
    


  • @mrjj thank u. It works but it only reads the last line. I want to read every line and show the screen one by one


  • Lifetime Qt Champion

    @suslucoder

    hi
    it does read all of the files but if you do
    ui -> plainTextEdit->setPlainText(line);
    you then replace all text with the line you just read, over and over. so it only show the last line in the end.

    so you want to do

    ui -> plainTextEdit->appendPlainText(line);

    https://doc.qt.io/qt-5/qplaintextedit.html#appendPlainText

    to add the lines as you read them.

    ps. you dont have to read it line by line if all you want is to read it all and put in plainText.
    https://doc.qt.io/qt-5/qtextstream.html#readAll

    QFile inputFile(fileName);
    if (inputFile.open(QIODevice::ReadOnly))
    {
      QTextStream in(&inputFile);
      QString all = in.readAll();
      ui -> plainTextEdit->setPlainText(all);
    }
    


  • @mrjj I got it. Thank you so much it works. If I add a timer to code, cann it writes one line to the screen every 20 seconds


  • Lifetime Qt Champion

    @suslucoder
    Hi
    Well not directly with that code as we loop until all is added.

    But you could do (pseudo code. didn't compile it)

    
     QStringList allLines; // this goes in .h as a class member
     int curIndex = 0; // this goes in .h as a class member
    
    QFile inputFile(fileName);
    if (inputFile.open(QIODevice::ReadOnly))
    {
       QTextStream in(&inputFile);
       while (!in.atEnd())
       {
          QString line = in.readLine();
          allLines.append(line); // add to list 
       }
       inputFile.close();
    }
    
        QTimer *timer = new timer(this);
        connect(timer, &QTimer::timeout, [this]() {
            QString line = allLines[curIndex]; // get a line from list
            ui -> plainTextEdit->setPlainText(line); // add the line
            if (curIndex < allLines.size() - 1 ) // if not at end of allLines 
                curIndex++; // raise index
        });
        timer->start(20000);
    
    
    
    
    
    


  • @mrjj thank you so much


  • Lifetime Qt Champion

    @suslucoder
    Np, i hope its not to much cheating if its an assignment :)



  • @mrjj hahah im newly graduated from university, I want to improve myself in Qt. That's why I think of different scenarios to challenge myself.


  • Lifetime Qt Champion

    @suslucoder
    Oh all good then. :)
    Thats a good idea as one mostly get better at coding, by coding.



  • @mrjj I didnt understand the idea behind --> connect(timer, &QTimer::timeout, this

    Cant we do this using signal and slot?

    There is an error like expected body of lambda expression



  • @mrjj Hey, i got ASSERT failure in QList<T>::operator[]: "index out of range" ERROR. I cannot understand why. Can you help me?


  • Lifetime Qt Champion

    @suslucoder
    hi
    its means you try to access some index in a list and that index is too big.
    I would guess on curIndex if it gets bigger than the allLines.size()
    or if allLines is empty.
    Did you load the file to the list before starting the timer ?

    its a lambda, yes, but you can also use a normal slot to do the same.



  • @mrjj ``` I couldnt find my mistake :(

    #include "mainwindow.h"
    #include "ui_mainwindow.h"
    #include <QFile>
    #include <QTextStream>
    #include <QMessageBox>
    #include <QTimer>
    #include <QList>
    #include <qlist.h>
    #include <QDebug>
    
    
    MainWindow::MainWindow(QWidget *parent)
        : QMainWindow(parent)
        , ui(new Ui::MainWindow)
    {
        ui->setupUi(this);
    
        QTimer *timer = new QTimer(this);
    
        connect(timer, SIGNAL(timeout()), SLOT(on_pushButton_clicked()));
    
        QString line = allLines[curIndex];
        ui->plainTextEdit->setPlainText(line);
        if(curIndex < allLines.size() - 1 ) {
            curIndex++;
        }
        
        
        timer->start(20000);
        
    }
    MainWindow::~MainWindow()
    {
        delete ui;
    }
    
    
    void MainWindow::on_pushButton_2_clicked()  //write
    {
        QFile file("C:/Users/ilknu/Documents/QFileDemo/abc.txt");
        if(!file.open(QFile::WriteOnly | QFile::Text )) {
    
            QMessageBox::warning(this, "title", "file not open");
    
    
        }
    
        QTextStream out (&file);
        QString text = ui->plainTextEdit->toPlainText();
        out << text;
        file.flush();
        file.close();
    
    
    }
    
    void MainWindow::on_pushButton_clicked()  //read
    {
    
        QFile file("C:/Users/ilknu/Documents/QFileDemo/abc.txt");
    
        // QMessageBox::warning(this, "title", "file not open");
        // QTextStream in (&file);
        //    while (!in.atEnd()) {
        //        QString text = in.readLine();
        //    }
    
        //QString text = in.readLine();
    
      if(file.open(QIODevice::ReadOnly)) {
          QTextStream in (&file);
          while (!in.atEnd()) {
    
             // QString line = in.readLine();
             //  ui -> plainTextEdit->setPlainText(all);
    
     QString line = in.readLine();
     allLines.append(line);
     
              }
     }
    
    
          file.close();  }
    
      //  file.close();
    

  • Lifetime Qt Champion

    Hi
    Well

    MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
    {
    ui->setupUi(this);

    QTimer *timer = new QTimer(this);
    
    connect(timer, SIGNAL(timeout()), SLOT(on_pushButton_clicked()));
    

    /// all this should be in the slot -> on_pushButton_clicked if that how you load it

    QString line = allLines[curIndex]; /// this will CRASH as you didnt fill list yet
    ui->plainTextEdit->setPlainText(line);
    if(curIndex < allLines.size() - 1 ) {
    curIndex++;
    }

    timer->start(20000);  /// do not start timer before you have loaded into list..
    

    So it was mostly the order of the code



  • @mrjj im so confused about the order of my code. I tried all combinations that come to my mind, but when i clicked the read button my application was ended forcefully :(


  • Lifetime Qt Champion

    @suslucoder
    Ok
    You want it like

    MainWindow::MainWindow(QWidget *parent)
        : QMainWindow(parent)
        , ui(new Ui::MainWindow)
    {
        ui->setupUi(this);
    
        QTimer *timer = new QTimer(this);
        connect(timer, SIGNAL(timeout()), SLOT(Timer_Slot()));   // NOTE  new slot for timer    
    }
    
    // new slot for timer..  also put in .h under public slots:
    void MainWindow::Timer_Slot() {
        QString line = allLines[curIndex];
        ui->plainTextEdit->setPlainText(line);
        if (curIndex < allLines.size() - 1 ) {
            curIndex++;
        }    
    }
    
    void MainWindow::on_pushButton_clicked()  //read
    {
    
        QFile file("C:/Users/ilknu/Documents/QFileDemo/abc.txt");
        if (file.open(QIODevice::ReadOnly)) {
            QTextStream in (&file);
            while (!in.atEnd()) {
                QString line = in.readLine();
                allLines.append(line);
    
            }
        }
        file.close();
        curIndex=0; // make sure we start from start
        timer->start(20000); // we have read the lines, start timer
    }
    
    


  • @mrjj It works. Thank you for your help.



  • @suslucoder said in Windows not responding on reading file from txt:

    It works

    so please don't forget to mark your post as solved!