Memory management for arguments to some Qt functions/constructors?

Question

I want to add items to a QTreeWidget when a button is pressed. I'm using the following code in my program:

void MainWindow::on_training_addButton_clicked()
{
    countertest++;
    QStringList slist;
    slist << QString::number(countertest);
    ui->trainingDataTreeWidget->addTopLevelItem(new QTreeWidgetItem(slist)); //case 1

    //QTreeWidgetItem* item = new QTreeWidgetItem(slist); //case 2
    //ui->trainingDataTreeWidget->addTopLevelItem(item);
    //delete item;
}

In both cases I allocated dynamic memory for a QTreeWidgetItem. In the second case, I deleted it after passing it to addTopLevelItem(), but I'm worried Qt might need it later. What's the proper way to go about this?

Answer 1

The QTreeWidget destructor will take care of the deletion, and hence the class the life-cycle of the items. Just drop your external delete. IT would cause QTreeWidget trying to delete a dangling pointer, which would be the well-known double deletion crash.

Here is the proof from the documentation as well as the source:

Documentation

QTreeWidget::~QTreeWidget()

Destroys the tree widget and all its items.

Source

/*!
  \internal

  Destroys this tree model.
*/

QTreeModel::~QTreeModel()
{
    clear();
    delete headerItem;
    rootItem->view = 0; 
    delete rootItem;
}

/*!
  \internal

  Removes all items in the model.
*/

void QTreeModel::clear()
{
    SkipSorting skipSorting(this);
    beginResetModel();
    for (int i = 0; i < rootItem->childCount(); ++i) {
        QTreeWidgetItem *item = rootItem->children.at(i);
        item->par = 0; 
        item->view = 0; 
        delete item;
    }    
    rootItem->children.clear();
    sortPendingTimer.stop();
    endResetModel();
}