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"index out of range"

  • Hello everyone.
    First of all thanks a lot for helping me.

    I am trying to get information from a .txt file.
    I have to get the first four words of each line.

    This is my code:

            ui->textEdit->setPlainText(file.readAll()); //Mostramos el texto en un a ventana
             pinta las líneas
                std::cout<<("Estoy en print_lines)")<< std::endl;
                QString texto = ui->textEdit->toPlainText();
                QStringList lines = texto.split("\n", QString::KeepEmptyParts); //Split the text in lines and save each line in Array called "lines"
                QStringList words;                                                                               //Por tanto ya tenemos todas las líneas en un array y podemos acceder a ellas como : linea1=myStringList(1);
                int num_lines = lines.size(); //number of lines that text has. (it always takes one line more that really it is)
                QString x_start[num_lines];
                QString y_start[num_lines];
                QString x_end[num_lines];
                QString y_end[num_lines];
                QString lines_split[num_lines];
                for (int i=0;i<num_lines-1;i++)
                    lines_split[i] = lines.at(i);
                    words = lines_split[i].split(" ", QString::SkipEmptyParts); //Split each line in words
                    x_start[i] = words.at(0); //Take the first word
                    y_start[i] = words.at(1); //Take the second word
                    x_end[i] = words.at(2); //Take the third word
                    y_end[i] = words.at(3); //Take the fourth word
                    std::cout<<i << " " << x_end[i].toStdString()<< std::endl;


    It compiles fine but it drops an error that it is the next:

    ASSERT failure in QList<T>::at: "index out of range", file ../../../Qt5.6.0/5.6/gcc_64/include/QtCore/qlist.h, line 531
    The program has unexpectedly finished.

    And it enters in for just once...

    Could everybody help me?

    Thanks a lot.

  • Lifetime Qt Champion

    You should debug your code to see what happens.

    One note: this line is wrong

    for (int i=0;i<num_lines-1;i++)
    // it should be
    for (int i=0;i<num_lines;i++)
    // else you skip last line

  • Moderators

    Hi, welcome to devnet.

    You split the original file contents using the QString::KeepEmptyParts option. This means that if there are any empty lines they will be stored as well. There's probably also a new line character at the end, that's why you think that it's one item more than there is. It's probably an empty item at the end.

    The above is the problem, because then you split each line and silently assume there are always at least 4 elements. If the line is empty the split will produce an empty list and referencing its 0,1,2,3 element is the out of range error.

    To correct the code use QString::SkipEmptyParts in your initial split of the file contents. This will make sure you've got no empty strings in the list.
    Then, after you split each line, make sure it actually has at least 4 elements and append the values to a list instead of using an index:

    QStringList x_start;
    QStringList y_start;
    QStringList x_end;
    QStringList y_end;
    for (int i = 0; i < num_lines; ++i) //go all the way, don't skip the last item
       words = lines.at(i).split(" ", QString::SkipEmptyParts);
       if (words.size() >= 4)
          x_start << words.at(0); //Take the first word
          y_start << words.at(1); //Take the second word
          x_end   << words.at(2); //Take the third word
          y_end   << words.at(3); //Take the fourth word
          std::cout << i << " " << x_end.last().toStdString() << std::endl;

  • @Chris-Kawa Thanks a lot for answering!
    now it works fine!!

  • @jsulm Yes my friend I want to skip last line because .size takes size of lines+1 but I do not know why...

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