UPDATE 2017-03-07

Using str.toUtf8() creates a temporary QByteArray; its lifetime is therefore tied to the lifetime of the variable it is assigned to. Using it as someFunc(str.toUtf8().data()) seems therefore a little bit undefined, as the returned array is only used for the duration of the call to .data(). At the very least, if there were multiple calls, like someFunc(foo.toUtf8().data(), bar.toUtf8().data()), the array pointed to by the first argument would be pointing to freed memory and therefore be gibberish. I would therefore not use the foo.toUtf8().data() at all, but instead rewrite the example as

QByteArray fooArr = foo.toUtf8();
QByteArray barArr = bar.toUtf8();
someFunc(fooArr.data(), barArr.data())

Better yet, rewrite the interfaces to use QStrings to as low a level as possible to avoid the string encodings altogether.

Q3ListBox -> QListWidget

Instead of Q3ListBox::text(i), we should use QListWidget::item(i)->text().

Instead of Q3ListBox::removeItem(i), we should probably use delete QListWidget::item(i).

QListWidget has insertItems() instead of insertStringList().

Instead of Q3ListBox::insertItem() with a single argument, QListWidget::addItem() should be used.

Deleting items matching a string in a QListWidget:

foreach(QListWidgetItem* listItem, widget->findItems(str, Qt::MatchFixedString))
  {
    delete listItem;
  }

Q3ListView -> QTreeWidget

QTreeWidget allows multiple selection. In cases where the Q3ListView was used to give back a single item, and this is still valid, use currentItem in the QTreeWidget. Properly handling multiple selection may be useful later. In many places, the code disabled sorting for a Q3ListView; this is not necessary with QTreeWidget as it should not automatically sort.

Number of columns must be set with setColumnCount(), this might be necessary to add later. Instead of tree->addColumn, the column headers should be set with tree->setHeaderLabel or tree->setHeaderLabels (the former just construct a list of single header).

Instead of Q3ListView::selectedItem, we should use QTreeWidget::currentItem.

Instead of Q3ListView::setSelected, we should use QTreeWidget::setCurrentItem.

Instead of Q3ListView::firstChild, we should use QTreeWidget::topLevelItem(0).

Instead of Q3ListView::childCount, we should use QTreeWidget::topLevelItemCount.

Instead of Q3ListView::setSortColumn(col), we should use QTreeWidget::sortItems(col, Qt::AscendingOrder). I'm not sure whether the semantics are exactly to same, and we might need a handler to sort the the widget when new items are added. In case of Q3ListView::setSortColumn(-1), we can just delete the call.

QTreeWidget has itemSelectionChanged() instead of selectionChanged(item *). There are very likely similar issues in other signals, luckily the program complains about misplaced slots and signals on startup.

Iterating over all items in QTreeWidget (QTreeWidgetItemIterator doc):

QTreeWidgetItemIterator it(widget);
while (*it)
  {
    QTreeWidgetItem *item = *it;
    // do something with item
    it++;
  }

Iterating over the first level of items:

for (int ii = 0; ii < widget->topLevelItemCount(); ii++)
  {
    QTreeWidgetItem *currItem = widget->topLevelItem(ii);
    // do something.
  }

QList<QString> list;
list <<  col1 << col2 << col3 << col4 << col5 << col6
    << col7 << col8;

QTreeWidgetItem *item = new QTreeWidgetItem(view, prev);
int idx = 0;
foreach(QString str, list) {
  item->setText(idx++, str);
}

if (lv->lastItem())
  new QTreeWidgetItem(lv, lv_view->lastItem(), str);
else
  new QTreeWidgetItem(lv, str);

QTreeWidgetItem *item = new QTreeWidgetItem(tw);
item->setText(0, str);

for (int ii = 0; ii < item->childCount(); ii++)
  {
    QTreeWidgetItem *currItem = item->child(ii);
    // do something.
  }

qDeleteAll(item->takeChildren());

Q3ButtonGroup and Q3GroupBox to QGroupBox

The only bigger issue here is that QGroupBox does not have selectedId(), instead, the radio buttons need to be either identified and queried separately, or enumerated through. In practice this is not a big issue, and in many places reduces use of magic, when the radio button was queried by its name instead of its location among other such radio buttons.

Q3ComboBox to QComboBox

QComboBox insertItem() requires index of the inserted item as an argument. Using container->count as argument should be ok, although naturally the correct index works as well :)

QComboBox::currentItem should be replaced with QComboBox::currentIndex.

QComboBox::text(i) should be replaced with QComboBox::itemText(i).

QTabWidget

QTabWidget::page should be replaced with QTabWidget::widget.

QTabWidget::currentPageIndex should be replaced with QTabWidget::currentIndex.

QTabWidget::setCurrentPage should be replaced with QTabWidget::setCurrentIndex.

(QTabWidget *)container::removePage(tab) should be replaced with container::removeTab(container->indexOf(tab)).

Layouts

no member named 'insert' in 'QGroupBox'

Instead of insert(), we should use addWidget() to a *Layout object, and set that to the QGroupBox.

QVBoxLayout *vbox = new QVBoxLayout;
vbox->addWidget(radio);
groupBox->setLayout(vbox);

Q3HBoxLayout *layout1 = new Q3HBoxLayout(0, 0, 6, "layout1")

The extra arguments can pretty safely be ignored. Spacing and margins can be set with setters separately.

Menus

Q3PopMenu to QMenu (thankfully no Q3Actions in the codebase).

QMenu does not have insertItem(), it has insertAction().

Instead of QMenu::text(i), we should use QMenu::actions()[0]->text()

Other changes and renamings

Q3Frame to QFrame.

The documentation indicates that perhaps what will be missed is frame around the butttons, and at this point this is not critical.

The Q3Frame took object name as a parameter, I guess this can be safely deleted when moving it to QFrame. It can be set with setObjectName() later, if necessary.

Q3TextEdit to QTextEdit.

Q3Table to QTableWidget

Error about missing member:

no member named
      'GuiClient' in 'QApplication'
Type type = QApplication::GuiClient

Fix is pretty non-controversial, the type has been nuked as the QApplication was split to QCoreApplication and QApplication, so just delete use from the app.

    no member named 'setPixmap' in 'QPushButton'
cip_left->setPixmap(QPixmap(":/left_arrow.png"));

From QIcon documentation, I think the following should be equivalent

button->setIcon(QIcon("open.xpm"));

container->label(i) should be replaced with container->tabText(i).

QWidget->setCaption should be replaced with QWidget->setWindowTitle.

QHeaderView->setMovable should be replaced with QHeaderView->setSectionsMovable.

QHeaderView->setResizeMode should be replaced with QHeaderView->setSectionResizeMode.

QSplitter::setResizeMode should be replaced with QSplitter::setStretchFactor. Described in the QSplitter compatibility document, also the QSplitter enums have disappeared, so the semantics of the call are different.

splitter->setResizeMode(firstChild, QSplitter::KeepSize);
splitter->setResizeMode(secondChild, QSplitter::Stretch);

should be rewritten as

splitter->setStretchFactor(splitter->indexOf(firstChild), 0);
splitter->setStretchFactor(splitter->indexOf(secondChild), 1);

Instead of QDir::convertSeparators we should use QDir::toNativeSeparators.

With

QMap<QTreeWidgetItem*, MyDataObject>::Iterator it;

we should use it.value() instead of it.data(), as described in the Qt4 doc of QMap iterators.

new QPushButton(this, "help"); should be rewritten as new QPushButton("help", this);, the text is now the first argument.

Use of setCentralWidget() in the app was weird, and caused the program to have a really funky layout. I wonder why it was not a problem with Qt4.