How to save a table in a file

[jsulm]

@Daesos Start your app with debugger (F5) and when it crashes check the stack trace to see where it crashes (use debug build of your app).

[J.Hilk]

@Daesos
Going through your code, I noticed, you're mixing postfix, prefix in your nested loop to access the Tablewidget Item. I would search there for an out of bounds error.

[JonB]

@Daesos
If you're still having problems with the file (once you've solved the "crash"), try replacing your QFile with a QString, and use https://doc.qt.io/Qt-5/qtextstream.html#QTextStream-3. You should be successfully building up the string of the file content. If that doesn't work, nor will write to file.

[Daesos]

I used debugger and when i click on pushButton_2 (save on interface) it returns a Segmentation Fault at "QTableWidgetItem::text".
@J.Hilk, I didn't even notice. I edited the increment.

Segmentation Fault occurs when I try to access to a NULL pointer, right? So, it might be out of bound.

[JonB]

@Daesos
I don't see save_button in the code you've posted?

I notice you have:

                ui->tableWidget->setItem(i, 0, itm);
                ui->tableWidget->setItem(i, 2, new QTableWidgetItem("Modified"));
                ui->tableWidget->setItem(i, 3, new QTableWidgetItem(newlist.at(j).lastModified().toString()));

Where do you setItem() on i, 1 ?

for(int i = 0; i < ui->tableWidget->rowCount(); ++i)
    for (int j = 1; j < ui->tableWidget->columnCount(); j++){
        QString txt(ui->tableWidget->item(i, j)->text());
        out<<txt;
    }

Check your accesses on every i, j here. Somewhere you do not have an item at item(i, j)!

[Daesos]

I've edited the increment:

   for(int i = 0; i < ui->tableWidget->rowCount(); ++i)
       for (int j = 1; j < ui->tableWidget->columnCount(); ++j)
           out<<ui->tableWidget->item(i, j)->text();

@JonB said in How to save a table in a file:

@Daesos

I notice you have:

                ui->tableWidget->setItem(i, 0, itm);
                ui->tableWidget->setItem(i, 2, new QTableWidgetItem("Modified"));
                ui->tableWidget->setItem(i, 3, new QTableWidgetItem(newlist.at(j).lastModified().toString()));

Where do you setItem() on i, 1 ?

I've inizialized item at (i, 1) before. Once inizialized the name of the file must not be modified. So I didn't use setItem on i, 1 again.

@Daesos
ui->tableWidget->setItem(ui->tableWidget->rowCount() - 1, 1, new QTableWidgetItem(newlist.at(index_new).fileName()));

[J.Hilk]

@Daesos said in How to save a table in a file:

for(int i = 0; i < ui->tableWidget->rowCount(); ++i)
for (int j = 1; j < ui->tableWidget->columnCount(); ++j)
out<<ui->tableWidget->item(i, j)->text();

Maybe it's time to #include good old <QDebug>

for(int i = 0; i < ui->tableWidget->rowCount(); ++i)
       for (int j = 1; j < ui->tableWidget->columnCount(); ++j){
           qDebug() << i << "of" << ui->tableWidget->rowCount() << endl
                             << j << "of" << ui->tableWidget->columnCount();
           out<<ui->tableWidget->item(i, j)->text();
           qDebug() << QString("Found text at %1 | %2").arg(i).arg(j);
       }

[VRonin]

Replace out<<ui->tableWidget->item(i, j)->text(); with out<<ui->tableWidget->model()->index(i, j).data().tostring(); to prevent segfaults

The problems I highlighted are still present though

@VRonin said in How to save a table in a file:

In your code above you are not:

• Writing any new line to separate rows.
• Writing any column separator
• Escaping column separators inside the data

[Daesos]

@VRonin In a previous version I've added both ";" and "\n", but I forgot to write them again.
However I forgot one case: what happen if I did not create/delete/modify any file, folder, or other?
The cells (i, 2) might be empty and here is where the program fails.
I resolved by editing some code:

void MainWindow::on_pushButton_2_clicked()
{
QFile csv(f_name);

if(!csv.open(QFile::WriteOnly))
    return;

QTextStream out(&csv);
int tmp_column = 0;

for(int i = 0; i < ui->tableWidget->rowCount(); ++i){
    for (int j = 1; j < ui->tableWidget->columnCount(); ++j){
        if(ui->tableWidget->item(i, j) != 0)
            out<<ui->tableWidget->item(i, j)->text();
            out<<";";
            tmp_column = j;
    }
    if(ui->tableWidget->item(i, tmp_column) != 0)
        out<<"\n";
}

out.flush();
csv.close();
}

It may not be quite good-looking but it works:

I've also prevented segmentation faults like this for example:

ui->tableWidget->setItem(index_delete, 0, itm);
    if(ui->tableWidget->item(index_delete, 2) != 0 && ui->tableWidget->item(index_delete, 2)->text() != "Deleted")
        ui->tableWidget->setItem(index_delete, 3, new QTableWidgetItem(QDateTime::currentDateTime().toString()));

[VRonin]

Try naming a folder Ugly; Name and save your model

[Daesos]

@VRonin You got me, this is another case to write.

[VRonin]

P.S.
new QTableWidgetItem(QDateTime::currentDateTime().toString()) see https://bugreports.qt.io/browse/QTBUG-65555

this should be separated in 3 lines:

QTableWidgetItem* tableItem = new QTableWidgetItem;
tableItem->setData(Qt::EditRole,QDateTime::currentDateTime());
ui->tableWidget->setItem(index_delete, 3,tableItem);

[Daesos]

Say I want to order the items of the table by name or date once I push Save, but without sorting the table itself (just the output in the file.csv). What can I do? Should I create a temporary table, order it and then store in the file?
Tell me if the question is not clear.

[VRonin]

Not a temporary table, you can use a QSortFilterProxyModel and then serialise the proxy rather than the original model.
Since your current architecture relies on the QStandardItem interface rether than the QAbstractItemModel one you'll need to do some rewriting.

To give you an idea, being QString m_csvSeparator the column separator:

#include <QStringBuilder>
QString escapedCSV(QString unexc) const
{
    if (!unexc.contains(m_csvSeparator))
        return unexc;
    unexc.replace(QLatin1Char('\"'), QStringLiteral("\"\""));
    return '\"' % unexc % '\"';

}
bool writeCsv(QTextStream& writer, const QAbstractItemModel* constModel) const
{
    if (!constModel)
        return false;
    for (int i = 0, maxRow = constModel->rowCount(); i < maxRow ; ++i) {
        for (int j = 0, maxCol = constModel->columnCount(); j < maxCol ; ++j) {
            const QString roleData = constModel->index(i, j).data().toString();
            if (j>0)
                writer << m_csvSeparator;
            if (!roleData.isEmpty()) 
                writer << escapedCSV(roleData);
        }
        writer << '\n';
    }
    return writer.status() == QTextStream::Ok;
}