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/*!
    \page porting4.html
    \title Porting to Qt 4
    \contentspage {Porting Guides}{Contents}
    \previouspage Porting Guides
    \nextpage Porting to Qt 4 - Virtual Functions
    \ingroup porting
    \brief An overview of issues and techniques to consider when porting from Qt 3 to Qt 4.

\omit
    ### QFileInfo::PermissionSpec -> QFile::Permission(s?)
    ### refer to porting4-renamedfunctions.qdoc
    ### QApplication library mutex is gone
    ### no integral conversion for containers? strings?
    ### QVector etc. are initialized to 0 by default?
    ### How to port from Qt 2.3 to Qt 4.
    ### missing sort() functions?
    ### QToolTipGroup
    ### QServerSocket -> Q3ServerSocket

    ### remove these when the classes are re-ported

    ### QApplication::eventLoop()

    \row \o void QCheckListItem::paintCell(QPainter *, const QColorGroup &, int, int, int)\row \o void Q3CheckListItem::paintCell(QPainter *, const QPalette &, int, int, int)
    \row \o void QCheckListItem::paintFocus(QPainter *, const QColorGroup &, const QRect &) \o void Q3CheckListItem::paintFocus(QPainter *, const QPalette &, const QRect &)
    \row \o QDataTable: a whole bunch of virtual functions have a different signature

    <     Function: void QIconViewItem::paintFocus(QPainter *, const QColorGroup &)
    >     Function: void QIconViewItem::paintFocus(QPainter *, const QPalette &)

    <     Function: void QIconViewItem::paintItem(QPainter *, const QColorGroup &)
    >     Function: void QIconViewItem::paintItem(QPainter *, const QPalette &)

    <     Function: bool QUrlOperator::checkValid()

    <     Function: void QWSInputMethod::setFont(const QFont &)

    ### OpenMode or OpenMode

    ### QWSDecoration
\endomit

    This document describes the process of porting applications from
    Qt 3 to Qt 4.
    If you haven't yet made the decision about porting, or are unsure
    about whether it is worth it, take a look at the \l{What's New in
    Qt 4}{key features} offered by Qt 4. See also
    \l{Moving from Qt 3 to Qt 4} for tips on how to write Qt 3 code
    that is easy to port to Qt 4.

    \bold{Other porting guides:}

    \list
    \o \l{Moving from Qt 3 to Qt 4} \mdash covers some high level topics relevant
       to developers porting from Qt 3 to Qt 4.
    \o \l{Porting to Qt 4 - Drag and Drop} \mdash covers differences in the
       way drag and drop is handled between Qt 3 and Qt 4.
    \o \l{Porting .ui Files to Qt 4} \mdash describes the new format used to
       describe forms created with \QD.
    \o \l{Porting to Graphics View} \mdash provides a class-by-class overview
       of the differences between Qt 3's canvas API and Qt 4's Graphics
       View framework.
    \o \l{qt3to4 - The Qt 3 to 4 Porting Tool} \mdash provides an overview
       of a tool aimed at helping developers start the process of porting an
       application to Qt 4.
    \endlist

    The Qt 4 series is not binary compatible with the 3 series. This
    means programs compiled for Qt 3 must be recompiled to work with
    Qt 4. Qt 4 is also not completely \e source compatible with 3,
    however nearly all points of incompatibility cause compiler
    errors or run-time messages (rather than mysterious results). Qt
    4 includes many additional features and discards obsolete
    functionality. Porting from Qt 3 to Qt 4 requires some effort,
    but once completed the considerable additional power and
    flexibility of Qt 4 is available for use in your applications.

    To port code from Qt 3 to Qt 4:

    \list 1

    \o Briefly read the porting notes below to get an idea of what to expect.

    \o Be sure that your code compiles and runs well on all your target
       platforms with Qt 3.

    \o Add the line \c{QT += qt3support} to your \c .pro file if you use
       \c qmake; otherwise, edit your makefile or project file to
       link against the Qt3Support library and add \c -DQT3_SUPPORT to your
       compiler flags. (You might also need to specify other
       libraries. See \l{What's New in Qt 4} for details.)

    \o Run the \l qt3to4 porting tool. The tool will go through your
       source code and adapt it to Qt 4.

    \o Follow the instructions in the \l{Porting .ui Files to Qt 4}
       page to port Qt Designer files.

    \o Recompile with Qt 4. For each error, search below for related
       identifiers (e.g., function names, class names). This document
       mentions all relevant identifiers to help you get the information
       you need at the cost of being a little verbose.

    \endlist

    The \l qt3to4 porting tool replaces occurrences of Qt 3 classes
    that don't exist anymore in Qt 4 with the corresponding Qt 3
    support class; for example, \c QListBox is turned into \c
    Q3ListBox.

    At some point, you might want to stop linking against the Qt 3
    support library (\l{Qt3Support}) and take advantage of Qt 4's
    new features. The instructions below explain how to do that for
    each compatibility class.

    In addition to the Qt3Support classes (such as \c Q3Action, \c
    Q3ListBox, and \c Q3ValueList), Qt 4 provides compatibility
    functions when it's possible for an old API to cohabit with the
    new one. For example, QString provides a
    QString::simplifyWhiteSpace() compatibility function that's
    implemented inline and that simply calls QString::simplified().
    \bold{The compatibility functions are not documented here; instead,
    they are documented for each class.}

    If you have the line \c{QT += qt3support} in your \c .pro file, \c
    qmake will automatically define the \c QT3_SUPPORT symbol, turning
    on compatibility function support. You can also define the symbol
    manually (e.g., if you don't want to link against the \c
    Qt3Support library), or you can define \c QT3_SUPPORT_WARNINGS
    instead, telling the compiler to emit a warning when a
    compatibility function is called. (This works only with GCC 3.2+
    and MSVC 7.)

    If you get stuck, ask on the
    \l{http://lists.trolltech.com/qt-interest/}{qt-interest}
    mailing list. If you are a licensed customer, you can also contact
    Qt's technical support team.

\omit
    ### what to do with slots that aren't slots anymore
    ### what to do with virtual functions that aren't virtual anymore
    ### what to do with virtual functions that changed signature
\endomit

\omit
    ### <qtl.h> -- stuff that vanished?
    ### implicit sharing
    ### uint -> int indexes
\endomit

    Table of contents:

    \tableofcontents{4}

\omit
    \section1 Header Files

    ### New style of headers

    \table
    \header \o Old header \o New header
    \row \o \c{<qtl.h>} \o \c{<qalgorithms.h>} or \c{<QtAlgorithms>}
    \endtable

    ### Some headers don't include each other anymore...
\endomit

    \section1 Casting and Object Types

    In Qt 3, it was possible to use the \c qt_cast() function to determine
    whether instances of QObject subclasses could be safely cast to derived
    types of those subclasses. For example, if a QFrame instance is passed
    to a function whose signature specifies a QWidget pointer as its argument,
    \c qt_cast() could be used to obtain a QFrame pointer so that the
    instance's functions can be accessed.

    In Qt 4, much of this functionality is provided by the qobject_cast()
    function, and additional functions also provide similar functionality for
    certain non-QObject types:

    \table
    \header \o Qt 3 function \o Qt 4 function
    \row    \o T *qt_cast<T *>(QObject *) \o \l{qobject_cast()}{T *qobject_cast<T *>(QObject *)}
    \row    \o                            \o \l{qgraphicsitem_cast()}{T qgraphicsitem_cast<T>(QGraphicsItem *)}
    \row    \o                            \o \l{qstyleoption_cast()}{T qstyleoption_cast<T>(QStyleOption *)}
    \row    \o                            \o \l{qvariant_cast()}{T qvariant_cast<T>(const QVariant &)}
    \row    \o                            \o \l{qdbus_cast()}{T qdbus_cast(const QDBusArgument &)}
    \endtable

\omit
    \section1 Global Functions

    \table
    \header \o Qt 3 function \o Qt 4 function
    \row \o cstrcmp() \o strcmp()
    \row \o cstrcpy() \o strcpy()
    \row \o cstrlen() \o strlen()
    \row \o cstrncmp() \o strncmp()
    \row \o qmemmove() \o memmove()
    \endtable

    qGLVersion() ###

    copyBlt() ###
    bitBlt()

    #ifdef compat classes:
        * QLayoutIterator
        * QColorGroup
        * QMenuItem

    QWidget visibleRect property compat
    QWidget::BackgroundOrigin compat
\endomit

    \section1 Type Names

    The table below lists the classes that have been renamed in Qt 4.
    If you compile your applications with \c QT3_SUPPORT defined, the
    old names will be available.

    Whenever you see an occurrence of the name on the left, you can
    safely replace it with the Qt 4 equivalent in your program. The
    \l qt3to4 tool performs the conversion automatically.

    \table
    \header \o Qt 3 class name \o Qt 4 class name
    \input porting4-renamedclasses.qdocinc
    \endtable

    The table below lists the enums and typedefs that have been
    renamed in Qt 4. If you compile your applications with \c
    QT3_SUPPORT defined, the old names will be available.

    Whenever you see an occurrence of the name on the left, you can
    safely replace it with the Qt 4 equivalent in your program. The
    \l qt3to4 tool performs the conversion
    automatically.

    \table
    \header \o Qt 3 type name \o Qt 4 type name
    \input porting4-renamedtypes.qdocinc
    \endtable

    \omit
    ###
    \row \o QButton::ToggleState \o Use QCheckBox::ToggleState instead.
    \endomit

    \section1 Enum Values

    The table below lists the enum values that have been renamed in
    Qt 4. If you compile your applications with \c QT3_SUPPORT defined,
    the old names will be available.

    Whenever you see an occurrence of the name on the left, you can
    safely replace it with the Qt 4 equivalent in your program. The
    \l qt3to4 tool performs the conversion automatically.

    \table
    \header \o Qt 3 enum value name \o Qt 4 enum value name
    \input porting4-renamedenumvalues.qdocinc
    \endtable

    In addition, the following \l{Qt::WindowFlags}{window flags} have
    been either replaced with \l{Qt::WidgetAttribute}{widget
    attributes} or have been deprecated:

    \table
    \header \o Qt 3 type \o Qt 4 equivalent
    \row \o Qt::WDestructiveClose \o Use QWidget::setAttribute(Qt::WA_DeleteOnClose) instead.
    \row \o Qt::WStaticContents \o{1,2} Use QWidget::setAttribute(Qt::WA_StaticContents) instead.
    \row \o Qt::WNorthWestGravity
    \row \o Qt::WNoAutoErase \o{1,3} Use QWidget::setAttribute(Qt::WA_NoBackground) instead.
    \row \o Qt::WResizeNoErase
    \row \o Qt::WRepaintNoErase
    \row \o Qt::WPaintClever \o Unnecessary in Qt 4.
         \omit ### Check with Matthias \endomit
    \row \o Qt::WMacNoSheet \o Unnecessary in Qt 4.
         \omit ### Check with Sam \endomit
    \endtable

    In Qt 4.1, the widget flags used to determine window modality were
    replaced by a single enum that can be used to specify the modal
    behavior of top-level widgets:

    \table
    \header \o Qt 3 type \o Qt 4 equivalent
    \row \o Qt::WShowModal \o Use QWidget::setWindowModality(Qt::ApplicationModal) instead.
    \row \o Qt::WGroupLeader \o Use QWidget::setWindowModality(Qt::WindowModal)
         for each child dialog of the group leader, but do not change the modality
         of the group leader itself.
    \endtable

    \target properties
    \section1 Properties

    Some properties have been renamed in Qt 4, to make Qt's API more
    consistent and more intuitive. For example, QWidget's \c caption
    property has been renamed \c windowTitle to make it clear that it
    refers to the title shown in the window's title bar.

    In addition, the property system has been extended to allow
    properties to be redefined in subclasses with the \l Q_PROPERTY()
    macro, removing the need for a \c Q_OVERRIDE() macro.

    The table below lists the Qt properties that have been renamed in
    Qt 4. Occurrences of these in \e{Qt Designer} \c .ui files are
    automatically converted to the new name by \c uic.

    \table
    \header \o Qt 3 name \o Qt 4 name
    \row \o QButton::accel \o QButton::shortcut
    \row \o QButton::on \o QButton::checked
    \row \o QButton::toggleButton \o QAbstractButton::checkable
    \row \o QDial::lineStep \o QDial::singleStep
    \row \o QDial::maxValue \o QDial::maximum
    \row \o QDial::minValue \o QDial::minimum
    \row \o QDialog::modal \o QDialog::isModal
    \row \o QLineEdit::edited \o QLineEdit::modified
    \row \o QLineEdit::hasMarkedText \o QLineEdit::hasSelectedText
    \row \o QLineEdit::markedText \o QLineEdit::selectedText
    \row \o QObject::name \o QObject::objectName
    \row \o QProgressDialog::progress \o QProgressDialog::value
    \row \o QProgressDialog::totalSteps \o QProgressDialog::maximum
    \row \o QProgressDialog::wasCancelled \o QProgressDialog::wasCanceled
    \row \o QPushButton::iconSet \o QPushButton::icon
    \row \o QScrollBar::draggingSlider \o QScrollBar::sliderDown
    \row \o QScrollBar::lineStep \o QScrollBar::singleStep
    \row \o QScrollBar::maxValue \o QScrollBar::maximum
    \row \o QScrollBar::minValue \o QScrollBar::minimum
    \row \o QSlider::lineStep \o QSlider::singleStep
    \row \o QSlider::maxValue \o QSlider::maximum
    \row \o QSlider::minValue \o QSlider::minimum
    \row \o QSpinBox::lineStep \o QSpinBox::singleStep
    \row \o QSpinBox::maxValue \o QSpinBox::maximum
    \row \o QSpinBox::minValue \o QSpinBox::minimum
    \row \o QTabBar::currentTab \o QTabBar::currentIndex
    \row \o QTabWidget::currentPage \o QTabWidget::currentWidget
    \row \o QToolButton::iconSet \o QToolButton::icon
    \row \o QToolButton::textLabel \o QToolButton::text
    \row \o QWidget::caption \o QWidget::windowTitle
    \row \o QWidget::icon \o QWidget::windowIcon
    \row \o QWidget::iconText \o QWidget::windowIconText
    \endtable

    A handful of properties in Qt 3 are no longer properties in Qt 4,
    but the access functions still exist as part of the Qt 4 API.
    These are not used by \e{Qt Designer}; the only case where you
    need to worry about them is in highly dynamic applications that
    use Qt's meta-object system to access properties. Here's the list
    of these properties with the read and write functions that you
    can use instead:

    \table
    \header \o Qt 3 property \o Qt 4 read function \o Qt 4 write function
    \row \o QSqlDatabase::connectOptions \o QSqlDatabase::connectOptions() \o QSqlDatabase::setConnectOptions()
    \row \o QSqlDatabase::databaseName \o QSqlDatabase::databaseName() \o QSqlDatabase::setDatabaseName()
    \row \o QSqlDatabase::hostName \o QSqlDatabase::hostName() \o QSqlDatabase::setHostName()
    \row \o QSqlDatabase::password \o QSqlDatabase::password() \o QSqlDatabase::setPassword()
    \row \o QSqlDatabase::port \o QSqlDatabase::port() \o QSqlDatabase::setPort()
    \row \o QSqlDatabase::userName \o QSqlDatabase::userName() \o QSqlDatabase::setUserName()
    \endtable

    Some properties have been removed from Qt 4, but the associated
    access functions are provided if \c QT3_SUPPORT is defined to help
    porting to Qt 4. When converting Qt 3 \c .ui files to Qt 4, \c uic
    generates calls to the Qt 3 compatibility functions. Note that
    this only applies to the properties of the Qt3Support library,
    i.e. \c QT3_SUPPORT properties of the other libraries must be
    ported manually when converting Qt 3 .ui files to Qt 4.

    The table below lists these properties with the read and write
    functions that you can use instead. The documentation for the
    individual functions explains how to replace them with
    non-compatibility Qt 4 functions.

    \table
    \header \o Qt 3 property \o Qt 4 read function (\c QT3_SUPPORT)\o Qt 4 write function (\c QT3_SUPPORT)
    \row \o QMenuBar::separator \o QMenuBar::separator() \o QMenuBar::setSeparator()
    \row \o QPushButton::menuButton \o QPushButton::isMenuButton() \o N/A
    \row \o QTabWidget::margin \o QTabWidget::margin() \o QTabWidget::setMargin()
    \row \o QTextEdit::textFormat \o QTextEdit::textFormat() \o QTextEdit::setTextFormat()
    \row \o QWidget::backgroundBrush \o QWidget::backgroundBrush() \o N/A
    \row \o QWidget::backgroundMode \o QWidget::backgroundMode() \o QWidget::setBackgroundMode()
    \row \o QWidget::backgroundOrigin \o QWidget::backgroundOrigin() \o QWidget::setBackgroundOrigin()
    \row \o QWidget::colorGroup \o QWidget::colorGroup() \o QWidget::setColorGroup()
    \row \o QWidget::customWhatsThis \o QWidget::customWhatsThis() \o QWidget::setCustomWhatsThis()
    \row \o QWidget::inputMethodEnabled \o QWidget::inputMethodEnabled() \o QWidget::setInputMethodEnabled()
    \row \o QWidget::ownCursor \o QWidget::ownCursor() \o N/A
    \row \o QWidget::ownFont \o QWidget::ownFont() \o N/A
    \row \o QWidget::ownPalette \o QWidget::ownPalette() \o N/A
    \row \o QWidget::paletteBackgroundColor \o QWidget::paletteBackgroundColor() \o QWidget::setPaletteBackgroundColor()
    \row \o QWidget::paletteBackgroundPixmap \o QWidget::paletteBackgroundPixmap() \o QWidget::setPaletteBackgroundPixmap()
    \row \o QWidget::paletteForegroundColor \o QWidget::paletteForegroundColor() \o QWidget::setPaletteForegroundColor()
    \row \o QWidget::underMouse \o QWidget::underMouse() \o N/A
    \endtable

    The following Qt 3 properties and their access functions are no
    longer available in Qt 4. In most cases, Qt 4 provides similar
    functionality.

    \table
    \header \o Qt 3 property \o Qt 4 equivalent
    \row \o QButton::autoRepeat \o N/A
    \row \o QButton::autoResize \o Call QWidget:setFixedSize(QWidget::sizeHint()) whenever you change the contents.
    \row \o QButton::exclusiveToggle \o See \l QAbstractButton::autoExclusive.
    \row \o QButton::pixmap \o Use QAbstractButton::icon instead.
    \row \o QButton::toggleState \o Use QCheckBox::setState() and QCheckBox::state() instead.
    \row \o QButton::toggleType \o Use QCheckBox::setTristate() instead.
    \row \o QComboBox::autoResize \o Call QWidget:setFixedSize(QWidget::sizeHint()) whenever you change the contents.
    \row \o QFrame::contentsRect \o Use Q3Frame::contentsRect() instead.
    \row \o QFrame::margin \o Use QWidget::setContentsMargins() instead.
    \row \o QTabBar::keyboardFocusTab \o N/A
    \row \o QToolButton::offIconSet \o Use the \l{QIcon::Off}{off component} of QAbstractButton::icon instead.
    \row \o QToolButton::onIconSet \o Use the \l{QIcon::On}{on component} of QAbstractButton::icon instead.
    \row \o QWidget::microFocusHint \o N/A
    \endtable

\omit
    \section1 Inheritance Chain

    ### QMenuBar, etc.

    \section1 Null vs. Empty

    ###
\endomit

    \section1 Explicit Sharing

    Qt 4 is the first version of Qt that contains no \link
    http://doc.trolltech.com/3.3/shclass.html explicitly shared
    \endlink classes. All classes that were explicitly shared in Qt 3
    are \e implicitly shared in Qt 4:

    \list
    \o QImage
    \o QBitArray
    \o QByteArray
    \o Q3PointArray
    \endlist

    This means that if you took a copy of an instance of the class
    (using operator=() or the class's copy constructor), any
    modification to the copy would affect the original and vice
    versa. Needless to say, this behavior is rarely desirable.

    Fortunately, nearly all Qt 3 applications don't rely on explicit
    sharing. When porting, you typically only need to remove calls to
    detach() and/or copy(), which aren't necessary anymore.

    If you deliberately rely on explicit sharing in your application,
    you can use pointers or references to achieve the same result in
    Qt 4.

    \oldcode
        void asciify(QByteArray array)
        {
            for (int i = 0; i < (int)array.size(); ++i) {
                if ((uchar)array[i] >= 128)
                    array[i] = '?';
            }
        }
    \newcode
        void asciify(QByteArray &array)
        {
            for (int i = 0; i < array.size(); ++i) {
                if ((uchar)array[i] >= 128)
                    array[i] = '?';
            }
        }
    \endcode

    (Notice the \c & in the parameter declaration.)

\omit
    \section1 Qt Designer .ui Files

    ###
\endomit

    \section1 Painting and Redrawing Widgets

    When implementing custom widgets in Qt 3, it was possible to use
    QPainter to draw on a widget outside paint events. This made it
    possible to integrate Qt applications with third party libraries
    and tools that impose their own rendering models. For example,
    a widget might be repainted in a slot using data obtained from
    an external source.

    In Qt 4, it is only possible to paint on a widget from within its
    \l{QWidget::}{paintEvent()} handler function. This restriction simplifies
    Qt's interaction with native window systems, improves the performance
    of applications by reducing the number of redraw operations, and
    also enables features to be implemented to improve the appearance of
    widgets, such as a backing store.

    Generally, we recommend redesigning applications to perform all
    painting operations in \l{QWidget::}{paintEvent()} functions, deferring
    actual painting until the next time this function is called.
    Applications can post paint events to trigger repaints, and it may be
    possible to examine your widget's internal state to determine which
    part of the widget needs to be repainted.

    If asynchronous repaints are used extensively by your application,
    and it is not practical to redesign the rendering model to perform
    all painting operations from within a widget's \l{QWidget::}{paintEvent()}
    function, it may be necessary to consider using an intermediate painting
    step. In this approach, one or more images can be updated asynchronously
    and painted on the widget in the paint event. To avoid excessive
    buffering, it may be worthwhile disabling the backing store by setting
    the widget's Qt::WA_PaintOnScreen widget attribute.

    On certain platforms, the Qt::WA_PaintOutsidePaintEvent widget attribute
    can be set to allow a widget to be painted from outside paint events.

    \note Setting widget attributes to disable key features of Qt's widget
    rendering model may also cause other features to be disabled.

    \section1 QAccel

    The \c QAccel class has been renamed Q3Accel and moved to the
    Qt3Support module. In new applications, you have three options:

    \list 1
    \o You can use QAction and set a key sequence using QAction::setShortcut().
    \o You can use QShortcut, a class that provides similar
       functionality to Q3Accel.
    \o You can use QWidget::grabShortcut() and process "shortcut"
       events by reimplementing QWidget::event().
    \endlist

    The Q3Accel class also supports multiple accelerators using the
    same object, by calling Q3Accel::insertItem() multiple times. In
    Qt 4, the solution is to create multiple QShortcut objects.

    \section1 QAccessibleInterface

    The QAccessibleInterface class has undergone some API changes in
    Qt 4, to make it more consistent with the rest of the Qt API.

    If you have classes that inherit QAccessibleInterface or one of
    its subclasses (QAccessibleObject, QAccessibleWidget, etc.), you
    must port them the new QAccessibleInterface API.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions}
    for a list of QAccessibleInterface virtual member functions in
    Qt 3 that are no longer virtual in Qt 4.

    \section1 QAccessibleTitleBar

    The \c QAccessibleTitleBar has been renamed Q3AccessibleTitleBar
    and moved to the Qt3Support library.

    \target qaction.section
    \section1 QAction

    The QAction class has been redesigned in Qt 4 to integrate better
    with the rest of the menu system. It unifies the old \c QMenuItem
    class and the old \c QAction class into one class, avoiding
    unnecessary data duplication and the need to learn two different
    APIs.

    The old \c QAction and \c QActionGroup classes have been renamed
    Q3Action and Q3ActionGroup and moved to Qt3Support. In addition,
    the new QAction class has compatibility functions to ease
    transition to Qt 4. Note that when using Q3ToolBar and
    Q3PopupMenu, their actions must be \l {Q3Action}s.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions}
    for a list of QAction virtual member functions in Qt 3 that are
    no longer virtual in Qt 4.

    \section1 QActionGroup

    The QAction class has been completely redesigned in Qt 4 to
    integrate better with the rest of the menu system. See the
    \l{#qaction.section}{section on QAction} for details.

    \section1 QApplication

    The QApplication class has been split into two classes:
    QCoreApplication and QApplication. The new QApplication class
    inherits QCoreApplication and adds GUI-related functionality. In
    practice, this has no consequences for existing Qt applications.

    In addition, the following API changes were made:

    \list 1
    \o  QApplication::allWidgets() and QApplication::topLevelWidgets()
        used to return a pointer to a QWidgetList. Now they return a
        QWidgetList.

        Also, QWidgetList has changed from being a typedef for
        QPtrList<QWidget> to being a typedef for QList<QWidget *>.
        See the \l{#qwidgetlist.section}{section on QWidgetList} below
        for details.

        \oldcode
            QWidgetList *list = QApplication::topLevelWidgets();
            QWidgetListIt it(*list);
            QWidget *widget;
            while ((widget = it.current())) {
                if (widget->inherits("MainWindow"))
                    ((MainWindow *)widget)->updateRecentFileItems();
                ++it;
            }
            delete list;
        \newcode
            QWidgetList list = QApplication::topLevelWidgets();
            for (int i = 0; i < list.size(); ++i) {
                if (MainWindow *mainWin = qobject_cast<MainWindow *>(list.at(i)))
                    mainWin->updateRecentFileItems();
            }
        \endcode
    \o QApplication::setMainWidget() is no longer used. When all an application's
       windows are closed, the application will exit normally.
    \endlist

    \section1 QAquaStyle

    The \c QAquaStyle class first appeared in Qt 3.0, when the Qt for
    Mac OS X port was first released. It emulated Apple's "Aqua" theme.
    In Qt 3.1, QAquaStyle was obsoleted by QMacStyle, which uses Appearance
    Manager to perform its drawing.

    The \c QAquaStyle class is no longer provided in Qt 4. Use
    QMacStyle instead.

    \target qasciidict.section
    \section1 QAsciiCache<T>

    \c QAsciiCache<T> has been renamed Q3AsciiCache<T> and moved to
    the Qt3Support library. It has been replaced by
    QCache<QByteArray, T>.

    For details, read the \l{#qcache.section}{section on QCache<T>},
    mentally substituting QByteArray for QString.

    \section1 QAsciiDict<T>

    QAsciiDict<T> and QAsciiDictIterator<T> have been renamed
    Q3AsciiDict<T> and Q3AsciiDictIterator<T> and moved to the
    Qt3Support library. They have been replaced by the
    more modern QHash<Key, T> and QMultiHash<Key, T> classes and
    their associated iterator classes.

    When porting old code that uses Q3AsciiDict<T> to Qt 4, there are
    four classes that you can use:

    \list
    \o QMultiHash<QByteArray, T *>
    \o QMultiHash<QByteArray, T>
    \o QHash<QByteArray, T *>
    \o QHash<QByteArray, T>
    \endlist

    For details, read the \l{#qdict.section}{section on QDict<T>},
    mentally substituting QByteArray for QString.

    \section1 QAsyncIO

    The \c QAsyncIO class was used internally in Qt 2.x in
    conjunction with QImageConsumer. It was obsoleted in Qt 3.0.

    \input porting4-obsoletedmechanism.qdocinc

    \section1 QBackInsertIterator

    The undocumented \c QBackInsertIterator class has been removed
    from the Qt library. If you need it in your application, feel
    free to copy the source code from the Qt 3 \c <qtl.h> header
    file.

    \section1 QBitArray

    In Qt 3, QBitArray inherited from QByteArray. In Qt 4, QBitArray
    is a totally independent class. This makes very little difference
    to the user, except that the new QBitArray doesn't provide any of
    QByteArray's byte-based API anymore. These calls will result in a
    compile-time error, except calls to QBitArray::truncate(), whose
    parameter was a number of \e bytes in Qt 3 and a number of bits
    in Qt 4.

    QBitArray was an explicitly shared class in Qt 3. See \l{Explicit
    Sharing} for more information.

    The \c QBitVal class has been renamed QBitRef.

    \section1 QButton

    The \c QButton class has been replaced by QAbstractButton in Qt
    4. Classes like QPushButton and QRadioButton inherit from
    QAbstractButton. As a help when porting older Qt applications,
    the Qt3Support library contains a Q3Button class
    implemented in terms of the new QAbstractButton.

    If you used the \c QButton class as a base class for your own
    button type and want to port your code to the newer
    QAbstractButton, you need to be aware that QAbstractButton has no
    equivalent for the Q3Button::drawButton(QPainter *) virtual
    function. The solution is to reimplement QWidget::paintEvent() in
    your QAbstractButton subclass as follows:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 0

    \table
    \header \o Q3Button function \o QAbstractButton equivalent
    \row \o Q3Button::autoResize() \o Call QWidget:setFixedSize(QWidget::sizeHint()) whenever you change the contents.
    \row \o Q3Button::isExclusiveToggle() \o Use QAbstractButton::group() or QAbstractButton::autoExclusive() instead.
    \row \o Q3Button::pixmap() const \o QAbstractButton::icon()
    \row \o Q3Button::setAutoResize() \o N/A
    \row \o Q3Button::setPixmap(const QPixmap &) \o QAbstractButton::setIcon(const QIcon &)
    \row \o Q3Button::setState(ToggleState) \o See remark below
    \row \o Q3Button::setToggleType(ToggleType) \o See remark below
    \row \o Q3Button::state() \o See remark below
    \row \o Q3Button::stateChanged(int) \o See remark below
    \row \o Q3Button::toggleType() \o See remark below
    \endtable

    Remarks:

    \list 1
    \o In Qt 3, \c QButton had a "toggle type", which could be
       QButton::SingleShot, QButton::Toggle, or QButton::Tristate.
       The new QAbstractButton class doesn't support "tristate"
       directly; this feature is implemented in QCheckBox instead.
       The two other "toggle types" (\c QButton::SingleShot and \c
       QButton::Toggle) are replaced by a QAbstractButton::checkable
       property.
    \o In Qt 3, QButton had a "toggle state", which could be \c
       QButton::Off, \c QButton::NoChange, or \c QButton::On. In Qt
       4, this mechanism has been moved to QCheckBox.
    \endlist

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of \c QButton virtual member functions in Qt 3 that aren't
    virtual in Qt 4.

    See \l{#properties}{Properties} for a list of \c QButton properties
    in Qt 3 that have changed in Qt 4.

    \section1 QButtonGroup

    The \c QButtonGroup class has been completely redesigned in Qt 4.
    For compatibility, the old \c QButtonGroup class has been renamed
    Q3ButtonGroup and has been moved to Qt3Support.
    Likewise, the \c QHButtonGroup and \c QVButtonGroup convenience
    subclasses have been renamed \c Q3HButtonGroup and \c Q3VButtonGroup and
    moved to the Qt3Support library.

    The old \c QButtonGroup, as well as Q3ButtonGroup, can be used in two ways:

    \list 1
    \o  The button group is the parent widget of a number of buttons,
        i.e. the button group is the parent argument in the button
        constructor. The buttons are assigned identifiers 0, 1, 2, etc.,
        in the order they are created. A Q3ButtonGroup can display a frame
        and a title because it inherits Q3GroupBox.
    \o  The button group is an invisible widget and the contained
        buttons have some other parent widget. In this usage, each
        button must be manually inserted, using
        Q3ButtonGroup::insert(), into the button group and given an
        ID number.
    \endlist

    Unlike Q3ButtonGroup, the new QButtonGroup doesn't inherit
    QWidget. It is very similar to a "hidden Q3ButtonGroup".

    If you use a Q3ButtonGroup, Q3HButtonGroup, or Q3VButtonGroup as
    a widget and want to port to Qt 4, you can replace it with
    QGroupBox. In Qt 4, radio buttons with the same parent are
    automatically part of an exclusive group, so you normally don't
    need to do anything else. See also the
    \l{#qgroupbox.section}{section on QGroupBox} below.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QButtonGroup virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \target qbytearray.section
    \section1 QByteArray

    In Qt 3, QByteArray was simply a typedef for QMemArray<char>. In
    Qt 4, QByteArray is a class in its own right, with a higher-level
    API in the style of QString.

    Here are the main issues to be aware of when porting to Qt 4:

    \list 1
    \o  The QMemArray(int size) constructor has been replaced with
        QByteArray(int size, char ch). The second argument specifies
        which character should be used for initializing the array;
        pass '\\0' if you have no specific needs.

        \oldcode
        QByteArray ba(64);
        \newcode
        QByteArray ba(64, '\0');
        \endcode

    \o  QMemArray::at() returned a non-const reference, whereas the
        new QByteArray::at() returns a const value. Code like

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 1

        will no longer compile. Instead, use QByteArray::operator[]:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 2

    \o  The QMemArray::contains(char) function has been renamed
        QByteArray::count(char). In addition, there now exists a
        QByteArray::contains(char) function that returns a boolean
        value. Replace old calls to contains() with either count() or
        contains(), depending on whether you care about the specific
        number of occurrences of a character in the byte array or
        only care about whether the array contains that character or
        not.

    \o  The new QByteArray has no assign() function. Calls to
        QMemArray::assign(const QMemArray &) can be replaced by calls
        to QByteArray::operator=(). Calls to QMemArray::assign(const
        T *, uint) have no equivalent in Qt 4; if you use it, the
        solution is either to use QByteArray::fromRawData() and to
        call free() yourself to avoid a memory leak, or to use the
        QByteArray(const char *, int) constructor, which will take a
        deep copy of the data.

    \o  QMemArray::bsearch() and QMemArray::sort() have no equivalent
        in the new QByteArray class. Use \l qBinaryFind() and \l qSort()
        if you need that functionality.
    \endlist

    QByteArray was an explicitly shared class in Qt 3. See
    \l{Explicit Sharing} for more information.

    \target qcache.section
    \section1 QCache<T>

    QCache<T> has been renamed Q3Cache<T> and moved to Qt3Support.
    The new QCache class has a different API, and takes different
    template parameters: QCache<Key, T>.

    When porting to Qt 4, QCache<QString, T> is the obvious
    substitute for Q3Cache<T>. The following table summarizes the API
    differences.

    \table
    \header \o Q3Cache<T> function \o QCache<QString, T> equivalent
    \row \o Q3Cache::Q3Cache(int maxCost, int size, bool caseSensitive) \o See remark below
    \row \o Q3Cache::autoDelete() \o N/A
    \row \o Q3Cache::count() \o QCache::count() or QCache::size() (equivalent)
    \row \o Q3Cache::setAutoDelete() \o See remark below
    \row \o Q3Cache::size() \o N/A
    \row \o Q3Cache::statistics() \o N/A
    \row \o Q3Cache::operator=() \o See remark below
    \endtable

    Remarks:

    \list 1
    \o  Q3Cache requires the user to allocate a specific number of
        buckets by passing a prime number (17 by default) to the
        constructor. In contrast, the new QCache's hash table
        automatically grows and shrinks as needed, and the
        constructor doesn't take a prime number.

    \o  Q3Cache supportes case-insensitive lookups by passing false as
        second argument to the constructor. This feature has no
        equivalent in QMultiHash. Instead, call QString::toLower()
        before you insert or lookup a key in the hash.

    \o  The Q3Cache::insert() function returns a \c bool value that
        indicates whether or not the item actually was inserted in
        the cache. If the item wasn't inserted, it was the caller's
        responsibility to delete the item. The new QCache::insert()
        function returns \c void and either adds it to the cache or
        deletes it right away. Old code like

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 3

    becomes

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 4

    \o  The new QCache class \e always takes ownership of the items
        it stores (i.e. auto-delete is always on). If you use Q3Cache
        with auto-delete turned off (the rarely useful default), you
        cannot use QCache as a direct substitute. One unelegant trick
        that works well in practice is to use QCache<QString, T *>
        instead of QCache<QString, T>. In that case, QCache owns the
        pointers, not the objects that the pointers refer to. For
        example,

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 5

        becomes

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 6

        An alternative is to stick to using Q3Cache.
    \endlist

    QCacheIterator<T> has been renamed Q3CacheIterator<T> and moved
    to the Qt3Support library. The new QCache class
    doesn't offer any iterator types.

    \section1 QCanvas

    The canvas module classes have been
    renamed and moved to the Qt3Support library.

    \table
    \header \o Qt 3 class name \o Compatibility class in Qt 4
    \row \o \c QCanvas \o Q3Canvas
    \row \o \c QCanvasEllipse \o Q3CanvasEllipse
    \row \o \c QCanvasItem \o Q3CanvasItem
    \row \o \c QCanvasItemList \o Q3CanvasItemList
    \row \o \c QCanvasLine \o Q3CanvasLine
    \row \o \c QCanvasPixmap \o Q3CanvasPixmap
    \row \o \c QCanvasPixmapArray \o Q3CanvasPixmapArray
    \row \o \c QCanvasPolygon \o Q3CanvasPolygon
    \row \o \c QCanvasPolygonalItem \o Q3CanvasPolygonalItem
    \row \o \c QCanvasRectangle \o Q3CanvasRectangle
    \row \o \c QCanvasSpline \o Q3CanvasSpline
    \row \o \c QCanvasSprite \o Q3CanvasSprite
    \row \o \c QCanvasText \o Q3CanvasText
    \row \o \c QCanvasView \o Q3CanvasView
    \endtable

    \l{The Graphics View Framework} replaces QCanvas. For more on porting to
    Graphics View, see \l{Porting to Graphics View}.

    \section1 QColor

    In Qt 4, QColor is a value type like QPoint or QRect. Graphics
    system-specific code has been implemented in QColormap.

    The \c QColor::maxColors() function has been replaced
    by QColormap::size().

    The \c QColor::numBitPlanes() function has been replaced
    by QColormap::depth().

    The \c QColor::setNamedColor() function no longer supports
    the named color in the same way as Qt 3. Qt 4's
    \l{QColor::}{setNamedColor()} uses the new W3C convention
    as stated 
    \l{http://www.w3.org/TR/SVG/types.html#ColorKeywords}{here}.

    \table
    \header \o{4,1} Predefined Qt Colors
    \row \o Qt::color0 \o Qt::color1 \o Qt::black \o Qt::white
    \row \o Qt::darkGray \o Qt::gray \o Qt::lightGray \o Qt::red
    \row \o Qt::green \o Qt::blue \o Qt::cyan \o Qt::magenta
    \row \o Qt::yellow \o Qt::darkRed \o Qt::darkGreen \o Qt::darkBlue
    \row \o Qt::darkCyan \o Qt::darkMagenta \o Qt::darkYellow \o Qt::transparent
    \endtable

    The predefined colors listed in the table above were static
    QColor objects in Qt 3. In Qt 4, they are enum values of type
    Qt::GlobalColor. Thanks to the implicit QColor(Qt::GlobalColor)
    constructor, the enum values are automatically converted to
    \l{QColor}s in most contexts. Occasionally, you might need a
    cast.

    \oldcode
        QColor lightCyan = Qt::cyan.light(180);
    \newcode
        QColor lightCyan = QColor(Qt::cyan).light(180);
    \endcode

    \section1 QColorGroup

    In Qt 3, a QPalette consisted of three QColorGroup objects. In Qt
    4, the (rarely used) QColorGroup abstraction has been eliminated.
    For source compatibility, a QColorGroup class is available when
    \c QT3_SUPPORT is defined.

    The new QPalette still works in terms of color groups, specified
    through enum values (QPalette::Active, QPalette::Disabled, and
    QPalette::Inactive). It also has the concept of a \e current
    color group, which you can set using
    QPalette::setCurrentColorGroup().

    The QPalette object returned by QWidget::palette() returns a
    QPalette initialized with the correct current color group for the
    widget. This means that if you had code like

    \badcode
        painter.setBrush(colorGroup().brush(QColorGroup::Text));
    \endcode

    you can simply replace colorGroup() with palette():

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 7

    \section1 QColorDrag

    The \c QColorDrag class has been renamed Q3ColorDrag and moved to
    the Qt3Support library. In Qt 4, use QMimeData
    instead and call QMimeData::setColor() to set the color.

    \section1 QComboBox

    In Qt 3, the list box used to display the contents of a \c QComboBox
    widget could be accessed by using the \c listBox() function. In Qt 4,
    the standard list box is provided by a QListView widget, and can be
    accessed with the \l{QComboBox::view()}{view()} function.

    \omit ### \endomit

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QComboBox virtual member functions in Qt 3 that are no longer
    virtual in Qt 4.

    \section1 QCString

    In Qt 3, QCString inherited from QByteArray. The main drawback
    of this approach is that the user had the responsibility of
    ensuring that the string is '\\0'-terminated. Another important
    issue was that conversions between \c QCString and QByteArray often
    gave confusing results. (See the
    \l{http://doc.trolltech.com/qq/qq05-achtung.html#qcstringisastringofchars}{Achtung!
    Binary and Character Data} article in \e{Qt Quarterly} for an
    overview of the pitfalls.)

    Qt 4 solves that problem by merging the QByteArray and \c QCString
    classes into one class called QByteArray. Most functions that
    were in \c QCString previously have been moved to QByteArray. The
    '\\0' issue is handled by having QByteArray allocate one extra
    byte that it always sets to '\\0'. For example:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 8

    The Qt3Support library contains a class called
    Q3CString that inherits from the new QByteArray class and that
    extends it to provide an API that is as close to the old \c QCString
    class as possible. Note that the following functions aren't
    provided by Q3CString:

    \list
    \o QCString::find(const QRegExp &, int)
    \o QCString::findRev(const QRegExp &, int)
    \o QCString::contains(const QRegExp &)
    \o QCString::replace(const QRegExp &, const char *)
    \endlist

    The following functions have lost their last parameter, which
    specified whether the search was case sensitive or not:

    \list
    \o QByteArray::find(char, int)
    \o QByteArray::find(const char *, int)
    \o QByteArray::findRev(char, int)
    \o QByteArray::findRev(const char *, int)
    \o QByteArray::contains(char)
    \o QByteArray::contains(const char *)
    \endlist

    In both cases, the solution is to convert the \c QCString to a
    QString and use the corresponding QString functions instead.

    Also be aware that \c QCString::size() (inherited from
    QByteArray) used to return the size of the character data \e
    including the '\\0'-terminator, whereas the new
    QByteArray::size() is just a synonym for QByteArray::length().
    This brings QByteArray in line with QString.

    When porting to Qt 4, occurrences of \c QCString should be
    replaced with QByteArray or QString. The following table
    summarizes the API differences between the Q3CString
    class and the Qt 4 QByteArray and QString classes:

    \table
    \header \o Q3CString function \o Qt 4 equivalent
    \row \o Q3CString::Q3CString(const char *, uint) \o See remark below
    \row \o Q3CString::Q3CString(int) \o QByteArray::QByteArray(int, char)
    \row \o Q3CString::leftJustify() \o QString::leftJustified()
    \row \o Q3CString::length() \o QByteArray::length() or QByteArray::size() (equivalent)
    \row \o Q3CString::lower() \o QByteArray::toLower()
    \row \o Q3CString::rightJustify() \o QString::rightJustified()
    \row \o Q3CString::setExpand() \o See remark below
    \row \o Q3CString::simplifyWhiteSpace() \o QByteArray::simplified()
    \row \o Q3CString::sprintf() \o QString::sprintf()
    \row \o Q3CString::stripWhiteSpace() \o QByteArray::trimmed()
    \row \o Q3CString::toDouble() \o QString::toDouble()
    \row \o Q3CString::toFloat() \o QString::toFloat()
    \row \o Q3CString::toInt() \o QString::toInt()
    \row \o Q3CString::toLong() \o QString::toLong()
    \row \o Q3CString::toShort() \o QString::toShort()
    \row \o Q3CString::toUInt() \o QString::toUInt()
    \row \o Q3CString::toULong() \o QString::toULong()
    \row \o Q3CString::toUShort() \o QString::toUShort()
    \row \o Q3CString::upper() \o QByteArray::toUpper()
    \endtable

    Remarks:

    \list 1
    \o  Q3CString(const char *str, uint max) constructs a string of
        length strlen(str) or \e max - 1, whichever is shorter.
        QByteArray(const char *data, int size) constructs a byte
        array containing exactly \e size bytes.

        \oldcode
            QCString str1("Hello", 4);           // "Hel"
            QCString str2("Hello world!", n);
        \newcode
            QByteArray str1("Hello", 3);
            QByteArray str2("Hello world!");
            str2.truncate(n - 1);
        \endcode

    \o  Q3CString::setExpand(uint index, char ch) has no equivalent in
        Qt 4.

        \oldcode
            QCString str("Hello world");
            str.setExpand(16, '\n');            // "Hello world     \n"
        \newcode
            QByteArray str("Hello world");
            while (str.size() < 16)
                str += ' ';
            str += '\n';
        \endcode
    \endlist

    Since the old \c QCString class inherited from QByteArray,
    everything that is said in the \l{#qbytearray.section}{QByteArray
    section} applies for \c QCString as well.

    \section1 QCustomEvent

    In Qt 3, developers could create a custom event by constructing
    a new QCustomEvent, and send relevant data to other components in
    the application by passing a void pointer, either on construction or
    using the setData() function. Objects could receive custom events
    by reimplementing the \l{QObject::customEvent()}{customEvent()}
    function, and access the stored data using the event's data()
    function.

    In Qt 4, custom events are created by subclassing
    QEvent. Event-specific data can be stored in a way that is
    appropriate for your application. Custom events are still
    delivered to each object's
    \l{QObject::customEvent()}{customEvent()} handler function, but as
    QEvent objects rather than as deprecated QCustomEvent objects.

    \section1 QDataBrowser

    The \c QDataBrowser class has been renamed Q3DataBrowser and
    moved to the Qt3Support library. In Qt 4.2, you should use the
    QDataWidgetMapper class to create data-aware forms.

    See \l{QtSql Module} for an overview of the new SQL
    classes.

    \section1 QDataPump

    The \c QDataPump class was used internally in Qt 2.x in
    conjunction with QImageConsumer. It was obsoleted in Qt 3.0.

    \input porting4-obsoletedmechanism.qdocinc

    \section1 QDataSink

    The \c QDataSink class was used internally in Qt 2.x in conjunction
    with QImageConsumer. It was obsoleted in Qt 3.0.

    \input porting4-obsoletedmechanism.qdocinc

    \section1 QDataSource

    The \c QDataSource class was used internally in Qt 2.x in
    conjunction with QImageConsumer. It was obsoleted in Qt 3.0.
    \input porting4-obsoletedmechanism.qdocinc

    \section1 QDataTable

    The \c QDataTable class has been renamed Q3DataTable and moved to
    the Qt3Support library. In Qt 4.2, you should use the
    QDataWidgetMapper class to create data-aware forms.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QDataView

    The \c QDataView class has been renamed Q3DataView and moved to
    the Qt3Support library. In Qt 4.2, you should use the
    QDataWidgetMapper class to create data-aware forms.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QDateEdit

    The QDateEdit class in Qt 4 is a convenience class based on
    QDateTimeEdit. The old class has been renamed Q3DateEdit and moved
    to the Qt3Support library.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of \c QDateEdit virtual member functions in Qt 3 that are
    no longer virtual in Qt 4.

    \section1 QDateTimeEditBase

    The \c QDateTimeEditBase class has been renamed
    Q3DateTimeEditBase and moved to Qt3Support. Use QDateTimeEdit or
    QAbstractSpinBox instead.

    \section1 QDateTimeEdit

    The old \c QDateTimeEdit class has been renamed
    Q3DateTimeEditBase and moved to Qt3Support. The new QDateTimeEdit
    in Qt 4 has been rewritten from scratch to provide a more
    flexible and powerful API.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QDateTimeEdit virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \section1 QDeepCopy<T>

    The \c QDeepCopy<T> class in Qt 3 provided a means of ensuring that
    implicitly shared and explicitly shared classes referenced unique
    data. This was necessary because the reference counting in Qt's
    container classes was done in a thread-unsafe manner.

    With Qt 4, \c QDeepCopy<T> has been renamed Q3DeepCopy<T> and
    moved to the Qt3Support library. Removing it from
    existing code is straightforward.

    \oldcode
        QString str1 = "I am a string";
        QDeepCopy<QString> str2 = str1;
        QString str3 = QDeepCopy<QString>(str2);
    \newcode
        QString str1 = "I am a string";
        QString str2 = str1;
        QString str3 = str2;
    \endcode

    \section1 QDial

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QDial virtual member functions in Qt 3 that are no longer
    virtual in Qt 4.

    See \l{#properties}{Properties} for a list of QDial properties in
    Qt 3 that have changed in Qt 4.

    \target qdict.section
    \section1 QDict<T>

    \c QDict<T> has been renamed Q3Dict<T> and moved to Qt3Support.
    It has been replaced by the more modern QHash<Key, T> and
    QMultiHash<Key, T> classes.

    When porting old code that uses QDict<T> to Qt 4, there are four
    classes that you can use:

    \table
    \header \o Qt 4 class \o When to use it
    \row \o QMultiHash<QString, T *>

         \o Since Q3Dict<T> is pointer-based and allows duplicate
            keys, this is usually the most straightforward conversion.

    \row \o QMultiHash<QString, T>

         \o If type \c T is an \l{assignable data type}, you can use
            \c T as the value type rather than \c{T *}. This often
            leads to nicer code.

    \row \o QHash<QString, T *>

         \o{1,2} If you don't use duplicate keys, you can use QHash
            instead of QMultiHash. QMultiHash inherits from QHash.

    \row \o QHash<QString, T>
    \endtable

    The APIs of Q3Dict<T> and QMultiHash<QString, T *> are quite
    similar. The main issue is that Q3Dict supports auto-delete
    whereas QMultiHash doesn't.

    \omit
    (See \l{What's Wrong with
    Auto-Delete} for an explanation of why the Qt 4 containers don't
    offer that feature.)
    \endomit

    The following table summarizes the API differences between the
    two classes:

    \table
    \header \o Q3Dict function \o QMultiHash equivalent
    \row \o Q3Dict::Q3Dict(int size, bool caseSensitive) \o See remarks below
    \row \o Q3Dict::autoDelete() \o N/A
    \row \o Q3Dict::count() \o QMultiHash::count() or QMultiHash::size() (equivalent)
    \row \o Q3Dict::find(const QString &) \o QMultiHash::value(const QString &)
    \row \o Q3Dict::remove(const QString &) \o QMultiHash::take(const QString &)
    \row \o Q3Dict::resize(uint) \o QMultiHash::reserve(int)
    \row \o Q3Dict::setAutoDelete() \o See discussion below
    \row \o Q3Dict::size() \o QMultiHash::capacity()
    \row \o Q3Dict::statistics() \o N/A
    \row \o Q3Dict::operator[](const QString &) \o See remark below
    \endtable

    Remarks:

    \list 1
    \o  Q3Dict requires the user to allocate a specific number of
        buckets by passing a prime number (17 by default) to the
        constructor and/or calling Q3Dict::resize() later on. In
        contrast, QMultiHash's hash table automatically grows and
        shrinks as needed, and the constructor doesn't take a prime
        number.

    \o  Q3Dict supportes case-insensitive lookups by passing false as
        second argument to the constructor. This feature has no
        equivalent in QMultiHash. Instead, call QString::toLower()
        before you insert or lookup a key in the hash.

    \o  Q3Dict::size() and QMultiHash::size() have different semantics.
        The former returns the number of buckets in the container, whereas
        the latter returns the number of \e items in the container.

    \o  If there are multiple items with the same key,
        Q3Dict::remove() removes only the most recently inserted item,
        whereas QMultiHash::remove() removes all items that share a
        particular key. To remove only the most recently inserted item,
        call QMultiHash::take().

    \o  Q3Dict has only one [] operator (Q3Dict::operator[]()),
        providing const access to an item's value. QMultiHash also
        has a non-const overload that can be used on the left side of
        the assignment operator. If you use the [] operator on a
        non-const QHash with an unexisting item, QHash will created
        an element and initialize it to be a null pointer. For that
        reason, Q3Dict::operator[] should be converted to
        QMultiHash::value(), not QMultiHash::operator[].

    \endlist

    If you use Q3Dict's auto-delete feature (by calling
    Q3Dict::setAutoDelete(true)), you need to do some more work. You
    have two options: Either you call \c delete yourself whenever you
    remove an item from the container, or you use
    QMultiHash<QString, T> instead of QMultiHash<QString, T *> (i.e.
    store values directly instead of pointers to values). Here, we'll
    see when to call \c delete.

    The following table summarizes the idioms that you need to watch
    out for if you want to call \c delete yourself.

    \table
    \header \o Q3Dict idiom \o QMultiHash idiom
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 9
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 10
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 11
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 12
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 13

        (also called from Q3Dict's destructor)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 14

        In 99% of cases, the following idiom also works:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 15

        However, it may lead to crashes if \c hash is referenced from
        the value type's destructor, because \c hash contains
        dangling pointers until clear() is called.
    \endtable

    Be aware that Q3Dict's destructor automatically calls clear(). If
    you have a Q3Dict data member in a custom class and use the
    auto-delete feature, you will need to call \c delete on all the
    items in the container from your class destructor to avoid a
    memory leak.

    Finally, \c QDictIterator<T> (renamed Q3DictIterator<T>) must
    also be ported. There are no fewer than four iterator classes
    that can be used as a replacement: QHash::const_iterator,
    QHash::iterator, QHashIterator, and QMutableHashIterator. The
    most straightforward class to use when porting is
    QHashIterator<QString, T *>. The following table summarizes the
    API differences:

    \table
    \header \o Q3DictIterator functions \o Qt 4 equivalent
    \row \o Q3DictIterator::count() \o QHash::count() or QHash::size()
    \row \o Q3DictIterator::current() \o QHashIterator::value()
    \row \o Q3DictIterator::currentKey() \o QHashIterator::key()
    \row \o Q3DictIterator::isEmpty() \o QHash::isEmpty()
    \row \o Q3DictIterator::toFirst() \o QHashIterator::toFront()
    \row \o Q3DictIterator::operator()() \o QHashIterator::value()
    \row \o Q3DictIterator::operator*() \o QHashIterator::value()
    \row \o Q3DictIterator::operator++() \o See remark below
    \endtable

    Be aware that QHashIterator has a different way of iterating than
    Q3DictIterator. A typical loop with Q3DictIterator looks like this:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 16

    Here's the equivalent QHashIterator loop:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 17

    See \l{Java-style iterators} for details.

    \section1 QDir

    The following functions used to have a boolean \c{acceptAbsPath}
    parameter that defaulted to true:

    \list
    \i QDir::filePath()
    \i QDir::absFilePath()
    \i QDir::cd()
    \i QDir::mkdir()
    \i QDir::rmdir()
    \i QDir::remove()
    \i QDir::rename()
    \i QDir::exists()
    \endlist

    In Qt 3, if \c acceptAbsPath is true, a file name starting with
    '/' is be returned without change; if \c acceptAbsPath is false,
    an absolute path is prepended to the file name. For example:

    \table
    \header \i Current directory   \i File name        \i \c acceptAbsPath \i File path
    \row    \i{1,2} /home/tsmith   \i{1,2} index.html  \i true             \i /home/tsmith/index.html
    \row                                               \i false            \i /home/tsmith/index.html
    \row    \i{1,2} /home/tsmith   \i{1,2} /index.html \i true             \i /index.html
    \row                                               \i false            \i /home/tsmith/index.html
    \endtable

    In Qt 4, this parameter is no longer available. If you use it
    in your code, you can check that QDir::isRelativePath() returns
    false instead.

    \oldcode
        QDir dir("/home/tsmith");
        QString path = dir.filePath(fileName, false);
    \newcode
        QDir dir("/home/tsmith");
        QString path;
        if (dir.isRelativePath(fileName))
            path = dir.filePath(fileName);
        else
            path = fileName;
    \endcode

    QDir::encodedEntryList() has been removed.

    fileInfoList(), entryInfoList(), and drives() now return a QList<QFileInfo>
    and not a QPtrList<QFileInfo> *. Code using these methods will not work with
    the Qt3Support library and must be adapted instead.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QDir virtual member functions in Qt 3 that are no longer
    virtual in Qt 4.

    QDir::match() now always matches case insensitively.

    QDir::homeDirPath() has been removed. Use QDir::home() instead, and
    extract the path separately.

    \section1 QDns

    Qt 3 used its own implementation of the DNS protocol and provided
    a low-level \c QDns class. Qt 4's QHostInfo class uses the system's \c
    gethostbyname() function from a thread instead.

    The old \c QDns class has been renamed Q3Dns and moved to the
    Qt3Support library. The new QHostInfo class has a
    radically different API: It consists mainly of two static
    functions, one of which is blocking (QHostInfo::fromName()), the
    other non-blocking (QHostInfo::lookupHost()). See the QHostInfo
    class documentation for details.

    \section1 QDockArea

    The \c QDockArea class has been renamed Q3DockArea and moved to
    the Qt3Support library. In Qt 4, QMainWindow handles
    the dock and toolbar areas itself. See the QMainWindow
    documentation for details.

    \section1 QDockWindow

    The old \c QDockWindow class has been renamed Q3DockWindow and
    moved to the Qt3Support library. In Qt 4, there is a
    new QDockWidget class with a different API. See the class
    documentation for details.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QDockWidget virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \note \l{Q3DockWindow}'s
    \l{Q3DockWindow::setHorizontallyStretchable()}{horizontallyStretchable}
    property can be achieved in QDockWidget with
    \l{QWidget#Size Hints and Size Policies}{size policies}.

    \section1 QDragObject

    The \c QDragObject class has been renamed Q3DragObject and
    moved to the Qt3Support library. In Qt 4, it has been
    replaced by the QMimeData class. See the class documentation for
    details.

    Note that the Q3DragObject::DragCopyOrMove drag and drop mode is
    interpreted differently to Qt 3's QDragObject::DragCopyOrMove mode.
    In Qt 3, a move operation was performed by default, and the user had
    to hold down the \key{Ctrl} key to perform a copy operation.
    In Qt 4, a copy operation is performed by default; the user has to
    hold down the \key{Shift} key to perform a move operation.

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QDropSite

    The \c QDropSite class has been renamed Q3DropSite and moved to
    the Qt3Support library.

    The QDropSite class has been obsolete ever since Qt 2.0. The only
    thing it does is call QWidget::setAcceptDrops(true).

    \oldcode
    class MyWidget : public QWidget, public QDropSite
    {
    public:
        MyWidget(const QWidget *parent)
            : QWidget(parent), QDropSite(this)
        {
        }
        ...
    }
    \newcode
    class MyWidget : public QWidget
    {
    public:
        MyWidget(const QWidget *parent)
            : QWidget(parent)
        {
            setAcceptDrops(true);
        }
        ...
    }
    \endcode

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QEditorFactory

    The \c QEditorFactory class has been renamed Q3EditorFactory and
    moved to the Qt3Support library.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QEventLoop

    In Qt 3, \c QEventLoop combined the Qt event loop and the event
    dispatching. In Qt 4, these tasks are now assigned to two
    distinct classes: QEventLoop and QAbstractEventDispatcher.

    If you subclassed QEventLoop to integrate with another library's
    event loop, you must subclass QAbstractEventDispatcher instead. See
    the class documentation for details.

    Developers using \c{QEventLoop::loopLevel()} in Qt 3 should use
    QCoreApplication::loopLevel() instead. Note that this function is
    marked as obsolete, but it is expected to be available for the
    lifetime of Qt 4.
    \omit ### mention virtual functions that aren't virtual anymore \endomit

    \omit
    \section1 QFile

    The QFile::readLine(QString&, Q_ULONG) method from qt3 has been removed
    in qt4, but this change in the QFile interface is not documented in the
    porting documentation as of qt-4.0.0-b1.
    \endomit

    \section1 QFileDialog

    The QFileDialog class in Qt 4 has been totally rewritten. It
    provides most of the functionality of the old \c QFileDialog
    class, but with a different API. Some functionality, such as the
    ability to preview files, is expected to be added in a later Qt 4
    release.

    The old \c QFileDialog, \c QFileIconProvider, and \c QFilePreview
    classes has been renamed Q3FileDialog, Q3FileIconProvider, and
    Q3FilePreview and have been moved to Qt3Support. You can use them
    if you need some functionality not provided yet by the new
    QFileDialog class.

    The following table lists which functions have been renamed or
    removed in Qt 4.

    \table
    \header \o Old function \o Qt 4 equivalent
    \row \o Q3FileDialog::addFilter(const QString &) \o See remark below
    \row \o Q3FileDialog::addLeftWidget(QWidget *) \o N/A
    \row \o Q3FileDialog::addRightWidget(QWidget *) \o N/A
    \row \o Q3FileDialog::addToolButton(QAbstractButton *, bool separator) \o N/A
    \row \o Q3FileDialog::addWidgets(QLabel *, QWidget *, QPushButton *) \o N/A
    \row \o Q3FileDialog::dir() \o QFileDialog::directory()
    \row \o Q3FileDialog::dirPath() \o QFileDialog::directory().path()
    \row \o Q3FileDialog::iconProvider() \o N/A
    \row \o Q3FileDialog::isContentsPreviewEnabled() \o N/A
    \row \o Q3FileDialog::isInfoPreviewEnabled() \o N/A
    \row \o Q3FileDialog::previewMode() \o N/A
    \row \o Q3FileDialog::rereadDir() \o N/A
    \row \o Q3FileDialog::resortDir() \o N/A
    \row \o Q3FileDialog::selectAll(bool) \o N/A
    \row \o Q3FileDialog::setContentsPreview(QWidget *, Q3FilePreview *) \o N/A
    \row \o Q3FileDialog::setContentsPreviewEnabled(bool) \o N/A
    \row \o Q3FileDialog::setDir(const QString &) \o QFileDialog::setDirectory(const QString &)
    \row \o Q3FileDialog::setFilters(const char **) \o Q3FileDialog::setFilters(const QStringList &)
    \row \o Q3FileDialog::setIconProvider(Q3FileIconProvider *) \o N/A
    \row \o Q3FileDialog::setInfoPreview(QWidget *, Q3FilePreview *) \o N/A
    \row \o Q3FileDialog::setInfoPreviewEnabled(bool) \o N/A
    \row \o Q3FileDialog::setPreviewMode(PreviewMode) \o N/A
    \row \o Q3FileDialog::setSelectedFilter(const QString &) \o QFileDialog::selectFilter(const QString &)
    \row \o Q3FileDialog::setSelectedFilter(int) \o See remark below
    \row \o Q3FileDialog::setSelection(const QString &) \o QFileDialog::selectFile(const QString &)
    \row \o Q3FileDialog::setShowHiddenFiles(bool) \o showHidden()
    \row \o Q3FileDialog::setUrl(const QUrlOperator &) \o N/A
    \row \o Q3FileDialog::showHiddenFiles() \o N/A
    \row \o Q3FileDialog::url() \o QUrl::fromLocalFile(QFileDialog::directory())
    \header \o Old signals \o Qt 4 equivalent
    \row \o Q3FileDialog::fileHighlighted(const QString &) \o N/A
    \row \o Q3FileDialog::fileSelected(const QString &) \o QFileDialog::filesSelected(const QStringList &)
    \row \o Q3FileDialog::dirEntered(const QString &) \o N/A
    \row \o Q3FileDialog::filterSelected(const QString &) \o N/A
    \endtable

    Remarks:

    \list 1
    \o  The Q3FileDialog::addFilter(const QString &) function has no
        direct equivalent in the new QFileDialog. Use
        QFileDialog::setFilters() instead.

        \oldcode
        fileDialog->addFilter(tr("JPEG files (*.jpg *.jpeg)"));
        \newcode
        QStringList filters = fileDialog->filters();
        filters << tr("JPEG files (*.jpg *.jpeg)");
        fileDialog->setFilters(filters);
        \endcode

    \o  The Q3FileDialog::setSelectedFilter(int) overload has no direct
        equivalent in the new QFileDialog. Use
        QFileDialog::selectFilter(const QString &) instead.

        \oldcode
        fileDialog->setSelectedFilter(3);
        \newcode
        fileDialog->selectFilter(fileDialog->filters().at(3));
        \endcode
    \endlist

    There are no equivalent virtual functions to the two
    Q3FileDialog::setSelectedFilter() virtual functions in the QFileDialog
    API. In addition, these functions have been renamed or removed, as
    described above.

    \section1 QFocusData

    The QFocusData class is not available in Qt 4. Some of its
    functionality is available via the QWidget::nextInFocusChain()
    and QWidget::focusNextPrevChild() functions.

    \section1 QFocusEvent

    The setReason() function is no longer present in Qt 4. It is
    necessary to define the reason when constructing a focus event.

    \section1 QFont

    \c QFont::Script has been moved to QFontDatabase::WritingSystem.

    \section1 QFrame

    The QFrame class has been made more lightweight in Qt 4, by
    reducing the number of properties and virtual functions. The
    reduction in the number of virtual functions is significant
    because QFrame is the base class of many Qt classes.

    Here's an overview of the changes:

    \list
    \o  QFrame no longer has a \c margin property (which wasn't
        honored by Qt's layout managers anyway).

    \o  QFrame no longer has a frameChanged() function, reimplement
        QFrame::resizeEvent() instead.

    \o  QFrame used to have drawFrame(QPainter *) and
        drawContents(QPainter *) virtual functions. These are now
        gone. In Qt 4, the frame is drawn by the QFrame::paintEvent()
        function. If you want to change the way QFrame paints itself,
        reimplement this function. To draw the contents of the frame,
        reimplement QFrame:paintEvent() and call the base class
        implementation of the function before you use the
        \l {QWidget::}{contentsRect()} function inherited from QWidget,
        to retrieve the rectangle to paint on.

    \endlist

    To help with porting, the Qt3Support library contains a Q3Frame
    class that inherits QFrame and provides a similar API to the old
    QFrame class. If you derived from QFrame in your application, you
    might want to use Q3Frame as a base class as a first step in the
    porting process, and later move on to the new QFrame class.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QFrame virtual member functions in Qt 3 that are no longer
    virtual in Qt 4.

    \section1 QFtp

    QFtp no longer inherits from QNetworkProtocol. See the
    \l{#qnetworkprotocol.section}{section on QNetworkProtocol} for
    details.

    The old \c QFtp class has been renamed Q3Ftp and moved to the
    Qt3Support library.

    \target qglayoutiterator.section
    \section1 QGLayoutIterator

    The QGLayoutIterator class no longer exists in Qt 4. This makes
    only a difference if you implemented custom layout managers
    (i.e., QLayout subclasses).

    The new approach is much simpler: It consists in reimplementing
    QLayout::itemAt() and QLayout::takeAt(). These functions operate
    on indexes, eliminating the need for a layout iterator class.

    \section1 QGrid

    The \c QGrid class is now only available as Q3Grid in Qt 4. You
    can achieve the same result as \c QGrid by creating a QWidget
    with a grid layout:

    \oldcode
    QGrid *grid = new QGrid(2, Qt::Horizontal);
    QPushButton *child1 = new QPushButton(grid);
    QPushButton *child2 = new QPushButton(grid);
    QPushButton *child3 = new QPushButton(grid);
    QPushButton *child4 = new QPushButton(grid);
    \newcode
    QWidget *grid = new QWidget;
    QPushButton *child1 = new QPushButton(grid);
    QPushButton *child2 = new QPushButton(grid);
    QPushButton *child3 = new QPushButton(grid);
    QPushButton *child4 = new QPushButton(grid);

    QVBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(child1, 0, 0);
    layout->addWidget(child2, 0, 1);
    layout->addWidget(child3, 1, 0);
    layout->addWidget(child4, 1, 1);
    grid->setLayout(layout);
    \endcode

    \section1 QGridLayout

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QGridLayout virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \section1 QGridView

    The \c QGridView class has been renamed Q3GridView and moved to
    the Qt3Support library. In Qt 4, we recommend that
    you use QTableView or QAbstractItemView for presenting tabular
    data.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \target qgroupbox.section
    \section1 QGroupBox

    The QGroupBox class has been redesigned in Qt 4. Many of the
    features of the old \c QGroupBox class can be obtained by using
    the Q3GroupBox class from the Qt3Support library.

    The new QGroupBox is more lightweight. It doesn't attempt to
    duplicate functionality already provided by QGridLayout, and it
    does not inherit from QFrame. As a result, the following members
    have been removed:

    \list
    \o Q3GroupBox::setColumns(), Q3GroupBox::columns()
    \o Q3GroupBox::setOrientation(), Q3GroupBox::orientation()
    \o Q3GroupBox::setInsideMargin(), Q3GroupBox::insideMargin()
    \o Q3GroupBox::addSpace()
    \endlist

    Naturally, the \c columns and \c orientation properties have also
    been removed.

    If you rely on some of the missing functionality in your
    application, you can use Q3GroupBox instead of QGroupBox as a
    help to porting.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of QGroupBox virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \section1 QHBox

    The \c QHBox class is now only available as Q3HBox in Qt 4. You
    can achieve the same result as \c QHBox by creating a QWidget
    with an horizontal layout:

    \oldcode
    QHBox *hbox = new QHBox;
    QPushButton *child1 = new QPushButton(hbox);
    QPushButton *child2 = new QPushButton(hbox);
    \newcode
    QWidget *hbox = new QWidget;
    QPushButton *child1 = new QPushButton;
    QPushButton *child2 = new QPushButton;

    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(child1);
    layout->addWidget(child2);
    hbox->setLayout(layout);
    \endcode

    Note that child widgets are not automatically placed into the widget's
    layout; you will need to manually add each widget to the QHBoxLayout.

    \section1 QHeader

    The \c QHeader class has been renamed Q3Header and moved to
    the Qt3Support library. In Qt 4, it is replaced
    by the QHeaderView class.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \section1 QHGroupBox

    The \c QHGroupBox class has been renamed Q3HGroupBox and moved to
    the Qt3Support library.
    Qt 4 does not provide a specific replacement class for \c QHGroupBox
    since QGroupBox is designed to be a generic container widget. As a
    result, you need to supply your own layout for any child widgets.

    See \l{#QGroupBox} for more information about porting code that uses
    group boxes.

    \section1 QHttp

    QHttp no longer inherits from QNetworkProtocol. See the See the
    \l{#qnetworkprotocol.section}{section on QNetworkProtocol} for
    details.

    The old \c QHttp, \c QHttpHeader, \c QHttpRequestHeader, and \c
    QHttpResponseHeader classes have been renamed Q3Http,
    Q3HttpHeader, Q3HttpRequestHeader, and Q3HttpResponseHeader  and
    have been moved to the Qt3Support library.

    \section1 QIconFactory

    The QIconFactory class is no longer part of Qt. It has been replaced by
    the QIconEngine class.

    \section1 QIconSet

    The QIconSet class is no longer part of Qt. It has been replaced by
    the QIcon class.

    \section1 QIconView

    The \c QIconView, \c QIconViewItem, \c QIconDrag, and \c
    QIconDragItem classes has been renamed Q3IconView,
    Q3IconViewItem, Q3IconDrag, and Q3IconDragItem and moved to the
    Qt3Support library. New Qt applications should use
    QListWidget or its base class QListView instead, and call
    QListView::setViewMode(QListView::IconMode) to obtain an "icon
    view" look.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \omit
    ###

    \section1 QImage

    QImage::fromMimeSource(const QString &) -> qImageFromMimeSource(const QString &)
    \endomit

    \section1 QImageDrag

    The \c QImageDrag class has been renamed Q3ImageDrag and moved to
    the Qt3Support library. In Qt 4, use QMimeData
    instead and call QMimeData::setImage() to set the image.

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QImageIO

    The \c QImageIO class has been split into two classes:
    QImageReader and QImageWriter. The table below shows the
    correspondance between the two APIs:

    \table
    \header \o Qt 3 function              \o Qt 4 equivalents
    \row    \o QImageIO::description()    \o QImageWriter::description()
    \row    \o QImageIO::fileName()       \o QImageReader::fileName() and QImageWriter::fileName()
    \row    \o QImageIO::format()         \o QImageReader::format() and QImageWriter::format()
    \row    \o QImageIO::gamma()          \o QImageWriter::gamma()
    \row    \o QImageIO::image()          \o Return value of QImageReader::read()
    \row    \o QImageIO::inputFormats()   \o QImageReader::supportedImageFormats()
    \row    \o QImageIO::ioDevice()       \o QImageReader::device() and QImageWriter::device()
    \row    \o QImageIO::outputFormats()  \o QImageWriter::supportedImageFormats()
    \row    \o QImageIO::parameters()     \o N/A
    \row    \o QImageIO::quality()        \o QImageWriter::quality()
    \row    \o QImageIO::read()           \o QImageReader::read()
    \row    \o QImageIO::setDescription() \o QImageWriter::setDescription()
    \row    \o QImageIO::setFileName()    \o QImageReader::setFileName() and QImageWriter::setFileName()
    \row    \o QImageIO::setFormat()      \o QImageReader::setFormat() and QImageWriter::setFormat()
    \row    \o QImageIO::setGamma()       \o QImageWriter::setGamma()
    \row    \o QImageIO::setIODevice()    \o QImageReader::setDevice() and QImageWriter::setDevice()
    \row    \o QImageIO::setImage()       \o Argument to QImageWriter::write()
    \row    \o QImageIO::setParameters()  \o N/A
    \row    \o QImageIO::setQuality()     \o QImageWriter::setQuality()
    \row    \o QImageIO::setStatus()      \o N/A
    \row    \o QImageIO::status()         \o QImageReader::error() and QImageWriter::error()
    \row    \o QImageIO::write()          \o QImageWriter::write()
    \endtable

    \section1 QIntCache<T>

    QIntCache<T> has been moved to Qt3Support. It has been replaced
    by QCache<int, T>.

    For details, read the \l{#qcache.section}{section on QCache<T>},
    mentally substituting \c int for QString.

    \section1 QIntDict<T>

    QIntDict<T> and QIntDictIterator<T> have been moved to
    Qt3Support. They have been replaced by the more modern QHash<Key,
    T> and QMultiHash<Key, T> classes and their associated iterator
    classes.

    When porting old code that uses QIntDict<T> to Qt 4, there are
    four classes that you can use:

    \list
    \o QMultiHash<int, T *>
    \o QMultiHash<int, T>
    \o QHash<int, T *>
    \o QHash<int, T>
    \endlist

    For details, read the \l{#qdict.section}{section on QDict<T>},
    mentally substituting \c int for QString.

    \target qiodevice.section
    \section1 QIODevice

    The QIODevice class's API has been simplified to make it easier
    to subclass and to make it work more smoothly with asynchronous
    devices such as QTcpSocket and QProcess.

    The following virtual functions have changed name or signature:

    \table
    \header \o Qt 3 function \o Comment
    \row \o QIODevice::at() const \o Renamed QIODevice::pos().
    \row \o QIODevice::at(Offset) \o Renamed QIODevice::seek().
    \row \o QIODevice::open(int) \o The parameter is now of type QIODevice::OpenMode.
    \row \o QIODevice::readBlock(char *, Q_ULONG) \o QIODevice::read(char *, qint64)
    \row \o QIODevice::writeBlock(const char *, Q_ULONG) \o QIODevice::write(const char *, qint64)
    \endtable

    \note QIODevice::open(QIODevice::OpenMode) is no longer pure virtual.

    The following functions are no longer virtual or don't exist anymore:

    \table
    \row \o QIODevice::getch() \o Renamed QIODevice::getChar() and implemented in terms of QIODevice::readData().
    \row \o QIODevice::putch(int) \o Renamed QIODevice::putChar() and implemented in terms of QIODevice::writeData().
    \row \o QIODevice::readAll() \o Implemented in terms of QIODevice::readData().
    \row \o QIODevice::readLine(char *, Q_ULONG) \o Implemented in terms of QIODevice::readData()
    \row \o QIODevice::ungetch(int) \o Renamed QIODevice::ungetChar() and simulated using an internal unget buffer.
    \endtable

    The \c IO_xxx flags have been revised, and the protected setFlags()
    function removed. Most of the flags have been
    eliminated because errors are best handled by implementing certain
    functions in QIODevice subclasses rather than through the base classes.
    The file access flags, such as \c IO_ReadOnly and \c IO_WriteOnly, have
    been moved to the QIODevice class to avoid polluting the global
    namespace. The table below shows the correspondence between the
    Qt 3 \c IO_xxx flags and the Qt 4 API:

    \table
    \header \o Qt 3 constant \o Qt 4 equivalent
    \row \o IO_Direct \o Use !QIODevice::isSequential() instead (notice the \e not).
    \row \o IO_Sequential \o Use QIODevice::isSequential() instead.
    \row \o IO_Combined \o N/A
    \row \o IO_TypeMask \o N/A
    \row \o IO_Raw \o QIODevice::Unbuffered
    \row \o IO_Async \o N/A
    \row \o IO_ReadOnly \o QIODevice::ReadOnly
    \row \o IO_WriteOnly \o QIODevice::WriteOnly
    \row \o IO_ReadWrite \o QIODevice::ReadWrite
    \row \o IO_Append \o QIODevice::Append
    \row \o IO_Truncate \o QIODevice::Truncate
    \row \o IO_Translate \o QIODevice::Text
    \row \o IO_ModeMask \o N/A
    \row \o IO_Open \o Use QIODevice::isOpen() instead.
    \row \o IO_StateMask \o N/A
    \row \o IO_Ok \o N/A
    \row \o IO_ReadError \o N/A
    \row \o IO_WriteError \o N/A
    \row \o IO_FatalError \o N/A
    \row \o IO_ResourceError \o N/A
    \row \o IO_OpenError \o N/A
    \row \o IO_ConnectError \o N/A
    \row \o IO_AbortError \o N/A
    \row \o IO_TimeOutError \o N/A
    \row \o IO_UnspecifiedError \o N/A
    \endtable

    \section1 QIODeviceSource

    The QIODeviceSource class was used internally in Qt 2.x in
    conjunction with QImageConsumer. It was obsoleted in Qt 3.0.
    \input porting4-obsoletedmechanism.qdocinc

    \section1 QLabel

    QLabel doesn't enable word-wrap automatically anymore when rich
    text is used. You can enable it by calling
    QLabel::setWordWrap() or by setting the
    \l{QLabel::wordWrap}{wordWrap} property. The reason for this
    change is that the old behavior was confusing to many users.

    Also, QLabel no longer offers an \c autoResize property. Instead,
    you can call QWidget::setFixedSize() on the label, with
    QLabel::sizeHint() as the argument, whenever you change the
    contents of the QLabel.

    See also \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions}
    for a list of QLabel virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \section1 QLayout

    In Qt 4, margins are always handled by layouts; there is no
    QLayout::setSupportsMargin() function anymore.

    The deleteAllItems() function is now only available if
    \c QT3_SUPPORT is defined. If you maintain a QList of layout
    items, you can use qDeleteAll() to remove all the items in one
    go.

    In Qt 3, it was possible to change the resizing behavior for layouts
    in top-level widgets by adjusting the layout's \c resizeMode property.
    In Qt 4, this property has been replaced by the QLayout::sizeConstraint
    property which provides more control over how the layout behaves when
    resized.

    See also the \l{#qlayoutiterator.section}{section on
    QLayoutIterator} and the \l{#qglayoutiterator.section}{section on
    QGLayoutIterator}.

    \target qlayoutiterator.section
    \section1 QLayoutIterator

    The QLayoutIterator class is obsoleted in Qt 4. It is available
    only if \c QT3_SUPPORT is defined. It can be replaced by the
    QLayout::itemAt() and QLayout::takeAt() functions, which operate
    on indexes.

    \oldcode
        QLayoutIterator it = layout()->iterator();
        QLayoutItem *child;
        while ((child = it.current()) != 0) {
            if (child->widget() == myWidget) {
                it.takeCurrent();
                return;
            ++it;
        }
    \newcode
        int i = 0;
        QLayoutItem *child;
        while ((child = layout()->itemAt(i)) != 0) {
            if (child->widget() == myWidget) {
                layout()->takeAt(i);
                return;
            }
            ++i;
        }
    \endcode

    \section1 QLineEdit

    See \l{#properties}{Properties} for a list of QLineEdit
    properties in Qt 3 that have changed in Qt 4.

    The default value of QLineEdit's \l{QLineEdit::dragEnabled()}{dragEnabled}
    property was \c true in Qt 3. In Qt 4, the default value is \c false.

    Note that QLineEdit in Qt 4 is no longer a subclass of QFrame.
    If you need to visually style a line edit with a frame, we recommend
    either using a QFrame as a container for a QLineEdit or customizing
    the line edit with a \l{Qt Style Sheets}{style sheet}.

    \section1 QListBox

    The \c QListBox, \c QListBoxItem, \c QListBoxText, and \c
    QListBoxPixmap classes have been renamed Q3ListBox,
    Q3ListBoxItem, Q3ListBoxText, and Q3ListBoxPixmap and have been
    moved to the Qt3Support library. New Qt applications
    should use QListWidget or its base class QListView instead.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \section1 QListView

    The \c QListView, \c QListViewItem, \c QCheckListItem, and \c
    QListViewItemIterator classes have been renamed Q3ListView,
    Q3ListViewItem, Q3CheckListItem, and Q3ListViewItemIterator, and
    have been moved to the Qt3Support library. New Qt
    applications should use one of the following four classes
    instead: QTreeView or QTreeWidget for tree-like structures;
    QListWidget or the new QListView class for one-dimensional lists.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \section1 QLocalFs

    The \c QLocalFs class is no longer part of the public Qt API. It
    has been renamed Q3LocalFs and moved to Qt3Support. Use QDir,
    QFileInfo, or QFile instead.

    \section1 QMainWindow

    The QMainWindow class has been redesigned in Qt 4 to provide a
    more modern look and feel and more flexibility. The API has
    changed to reflect that. The old \c QMainWindow class has been
    renamed Q3MainWindow and moved to Qt3Support. See the QMainWindow
    class documentation for details.

    \omit ### More detail \endomit

    \target qmemarray.section
    \section1 QMemArray<T>

    QMemArray<T> has been moved to Qt3Support. It has been replaced
    by the QVector<T> class.

    The following table summarizes the API differences between the
    two classes.

    \table
    \row \o QMemArray::assign(const QMemArray<T> &) \o QVector::operator=()
    \row \o QMemArray::assign(const T *, uint) \o See remark below
    \row \o QMemArray::duplicate(const QMemArray &) \o QVector::operator=()
    \row \o QMemArray::duplicate(const T *, uint) \o See remark below
    \row \o QMemArray::setRawData(const T *, uint) \o N/A
    \row \o QMemArray::resetRawData(const T *, uint) \o N/A
    \row \o QMemArray::find(const T &, uint) \o QVector::indexOf(const T &, int)
    \row \o QMemArray::contains(const T &) \o QVector::count(const T &)
    \row \o QMemArray::sort() \o \l qSort()
    \row \o QMemArray::bsearch(const T &d) \o \l qBinaryFind()
    \row \o QMemArray::at(uint) \o QVector::operator[]()
    \row \o QMemArray::operator const T *() \o QVector::constData()
    \endtable

    Remarks:

    \list 1
    \o  QMemArray::assign(const T *, uint) and QMemArray::duplicate(const T *, uint)
        can be replaced by QVector::resize() and qCopy().

        \oldcode
        QMemArray<QSize> array;
        ...
        array.assign(data, size);
        \newcode
        QVector<QSize> vector;
        ...
        vector.resize(size);
        qCopy(data, data + size, vector.begin());
        \endcode

    \o  QMemArray is an explicitly shared class, whereas QVector is
        implicitly shared. See \l{Explicit Sharing} for more
        information.
    \endlist

    \section1 QMenuBar

    In Qt 3, QMenuBar inherited from QFrame and QMenuData; in Qt 4, it is
    a direct subclass of QWidget. Applications that provided customized
    menu bars will need to take advantage of the styling features described
    in the \l{Qt Style Sheets} document.

    It is not possible to add widgets to menu bars in Qt 4.

    \section1 QMenuData

    In Qt 4, the QMenu class provides a menu widget that can be used in all
    the places where menus are used in an application. Unlike \c QMenuData,
    QMenu is designed around the concept of actions, provided by the QAction
    class, instead of the identifiers used in Qt 3.

    In Qt 3, it was possible to insert widgets directly into menus by using
    a specific \c QMenuData::insertItem() overload. In Qt 4.2 and later,
    the QWidgetAction class can be used to wrap widgets for use in Qt 4's
    action-based APIs.

    \section1 QMessageBox

    The QMessageBox::iconPixmap() function used to return a "const
    QPixmap *". In Qt 4, it returns a QPixmap.

    \section1 QMimeSourceFactory

    The \c QMimeSourceFactory has been renamed Q3MimeSourceFactory
    and moved to the Qt3Support library. New Qt applications should
    use Qt 4's \l{Resource System} instead.

    \section1 QMovie

    The QMovie API has been revised in Qt 4 to make it more
    consistent with the other Qt classes (notably QImageReader). The
    table below summarizes the changes.

    \table
    \header \o Qt 3 function \o Qt 4 equivalent
    \row \o QMovie::connectResize() \o Connect to QMovie::resized()
    \row \o QMovie::connectStatus() \o Connect to QMovie::stateChanged()
    \row \o QMovie::connectUpdate() \o Connect to QMovie::updated()
    \row \o QMovie::disconnectResize() \o Disconnect from QMovie::resized()
    \row \o QMovie::disconnectStatus() \o Disconnect from QMovie::stateChanged()
    \row \o QMovie::disconnectUpdate() \o Disconnect from QMovie::updated()
    \row \o QMovie::finished() \o Use QMovie::state() instead
    \row \o QMovie::frameImage() \o Use QMovie::currentImage() instead
    \row \o QMovie::frameNumber() \o Use QMovie::currentFrameNumber() instead
    \row \o QMovie::framePixmap() \o Use QMovie::currentPixmap() instead
    \row \o QMovie::getValidRect() \o Use frameRect() instead
    \row \o QMovie::isNull() \o Use QMovie::isValid() instead
    \row \o QMovie::pause() \o Use QMovie::setPaused(true) instead
    \row \o QMovie::paused() \o Use QMovie::state() instead
    \row \o QMovie::pushData() \o N/A
    \row \o QMovie::pushSpace() \o N/A
    \row \o QMovie::restart() \o Use QMovie::jumpToFrame(0) instead
    \row \o QMovie::running() \o Use QMovie::state() instead
    \row \o QMovie::step() \o Use QMovie::jumpToFrame() and QMovie::setPaused() instead
    \row \o QMovie::step() \o Use QMovie::jumpToNextFrame() instead
    \row \o QMovie::steps() \o Use QMovie::currentFrameNumber() and QMovie::frameCount() instead
    \row \o QMovie::unpause() \o Use QMovie::setPaused(false) instead
    \endtable

    \section1 QMultiLineEdit

    The \c QMultiLineEdit class in Qt 3 was a convenience QTextEdit
    subclass that provided an interface compatible with Qt 2's
    QMultiLineEdit class. In Qt 4, it is called Q3MultiLineEdit, it
    inherits Q3TextEdit, and it is part of Qt3Support. Use QTextEdit
    in new code.

    \target qnetworkprotocol.section
    \section1 QNetworkProtocol

    The QNetworkProtocol, QNetworkProtocolFactoryBase,
    QNetworkProtocolFactory<T>, and QNetworkOperation classes are no
    longer part of the public Qt API. They have been renamed
    Q3NetworkProtocol, Q3NetworkProtocolFactoryBase,
    Q3NetworkProtocolFactory<T>, and Q3NetworkOperation and have been
    moved to the Qt3Support library.

    In Qt 4 applications, you can use classes like QFtp and QHttp
    directly to perform file-related actions on a remote host.

    \section1 QObject

    QObject::children() now returns a QObjectList instead of a
    pointer to a QObjectList. See also the comments on QObjectList
    below.

    Use QObject::findChildren() (or qFindChildren() if you need MSVC 6
    compatibility) instead of QObject::queryList(). For example:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 18

    QObject::killTimers() has been removed because it was unsafe to
    use in subclass. (A subclass normally doesn't know whether the
    base class uses timers or not.)

    The \c QObject::name property has been renamed
    QObject::objectName.

    \c QObject::objectTrees() has been removed. If you are primarly
    interested in widgets, use QApplication::allWidgets() or
    QApplication::topLevelWidgets().

    \section1 QObjectDictionary

    The QObjectDictionary class is a synonym for
    QAsciiDict<QMetaObject>. See the \l{#qasciidict.section}{section
    on QAsciiDict<T>}.

    \section1 QObjectList

    In Qt 3, the QObjectList class was a typedef for
    QPtrList<QObject>. In Qt 4, it is a typedef for QList<QObject *>.
    See the \l{#qptrlist.section}{section on QPtrList<T>}.

    \section1 QPaintDevice

    To reimplement painter backends one previously needed to reimplement
    the virtual function QPaintDevice::cmd(). This function is taken out
    and should is replaced with the function QPaintDevice::paintEngine()
    and the abstract class QPaintEngine. QPaintEngine provides virtual
    functions for all drawing operations that can be performed on a
    painter backend.

    bitBlt() and copyBlt() are now only compatibility functions. Use
    QPainter::drawPixmap() instead.

    \section1 QPaintDeviceMetrics

    All functions that used to be provided by the \c
    QPaintDeviceMetrics class have now been moved to QPaintDevice.

    \oldcode
        QPaintDeviceMetrics metrics(widget);
        int deviceDepth = metrics.depth();
    \newcode
        int deviceDepth = widget->depth();
    \endcode

    For compatibility, the old \c QPaintDeviceMetrics class has been
    renamed Q3PaintDeviceMetrics and moved to Qt3Support.

    \section1 QPainter

    The QPainter class has undergone some changes in Qt 4 because of
    the way rectangles are drawn. In Qt 4, the result of drawing a
    QRect with a pen width of 1 pixel is 1 pixel wider and 1 pixel
    taller than in Qt 3.

    For compatibility, we provide a Q3Painter class in Qt3Support
    that provides the old semantics. See the Q3Painter documentation
    for details and for the reasons why we had to make this change.

    The \l{http://doc.trolltech.com/3.3/qpainter.html#CoordinateMode-enum}{QPainter::CoordinateMode}
    enum has been removed in Qt 4. All clipping
    operations are now defined using logical coordinates and are subject
    to transformation operations.

    The
    \l{http://doc.trolltech.com/3.3/qpainter.html#RasterOP-enum}{QPainter::RasterOP}
    enum has been replaced with QPainter::CompositionMode.

    \section1 QPicture

    In Qt 3, a QPicture could be saved in the SVG file format. In Qt
    4, the SVG support is provided by the QtSvg module, which
    includes classes for \e displaying the contents of SVG files.

    If you would like to generate SVG files, you can use the Q3Picture
    compatibility class or the QSvgGenerator class introduced in Qt 4.3.

    \section1 QPixmap

    The mask() function has been changed to return a reference to a QBitmap
    rather than a pointer. As a result, it is no longer possible simply to
    test for a null pointer when determining whether a pixmap has a mask.
    Instead, you need to explicitly test whether the mask bitmap is null or
    not.

    \oldcode
        if (pixmap.mask())
            widget->setMask(*pixmap.mask());
    \newcode
        if (!pixmap.mask().isNull())
            widget->setMask(pixmap.mask());
    \endcode

    The \c QPixmap::setOptimization() and \c QPixmap::setDefaultOptimization()
    mechanism is no longer available in Qt 4.

\omit
    QPixmap::fromMimeSource(const QString &) -> qPixmapFromMimeSource(const QString &)
\endomit

    \section1 QPointArray

    The \c QPointArray class has been renamed QPolygon in Qt 4 and
    has undergone significant changes. In Qt 3, \c QPointArray
    inherited from QMemArray<QPoint>. In Qt 4, QPolygon inherits from
    QVector<QPoint>. Everything mentioned in the
    \l{#qmemarray.section}{section on QMemArray<T>} apply for
    QPointArray as well.

    The Qt3Support library contains a Q3PointArray class
    that inherits from QPolygon and provides a few functions that
    existed in \c QPointArray but no longer exist in QPolygon. These
    functions include Q3PointArray::makeArc(),
    Q3PointArray::makeEllipse(), and Q3PointArray::cubicBezier().
    In Qt 4, we recommend that you use QPainterPath for representing
    arcs, ellipses, and Bezier curves, rather than QPolygon.

    The QPolygon::setPoints() and QPolygon::putPoints() functions
    return \c void in Qt 4. The corresponding Qt 3 functions returned
    a \c bool indicating whether the array was successfully resized
    or not. This can now be checked by checking QPolygon::size()
    after the call.

\omit
    X11 Specific:

    ::appDisplay() -> QX11Info::display()
    QPaintDevice::x11Display() -> QX11Info::display()
    QPaintDevice::x11AppDisplay() -> QX11Info::display()
    QPaintDevice::x11Screen() -> QX11Info::appScreen()
    QPaintDevice::x11AppScreen() -> ???
    QPaintDevice::x11Depth() -> QX11Info::appDepth()
    QPaintDevice::x11ColorMap() -> QX11Info::appColorMap()
    QPaintDevice::x11DefaultColorMap() -> ???
    QPaintDevice::x11Visual() -> QX11Info::appVisual()
    QPaintDevice::x11DefaultVisual() -> ???

    QPaintDevice::x11AppDpiX() -> QX11Info::appDpiX()
    QPaintDevice::x11AppDpiY() -> QX11Info::appDpiY()
    QPaintDevice::x11SetAppDpiX() -> QX11Info::setAppDpiX()
    QPaintDevice::x11SetAppDpiY() -> QX11Info::setAppDpiY()

    QPaintDevice::x11AppDepth() -> ???
    QPaintDevice::x11AppCells() -> ???
    QPaintDevice::x11AppRootWindow() -> ???
    QPaintDevice::x11AppColorMap() -> ???
    QPaintDevice::x11AppDefaultColorMap() -> ???
    QPaintDevice::x11AppVisual() -> ???
    QPaintDevice::x11AppDefaultVisual() -> ???

    End of X11 Specific
\endomit

    \section1 QPopupMenu

    For most purposes, QPopupMenu has been replaced by QMenu in Qt
    4. For compatibility with older applications, Q3PopupMenu provides
    the old API and features that are specific to pop-up menus. Note
    that, when using Q3PopupMenu, the menu's actions must be \l
    {Q3Action}s.

    In Qt 3, it was common practice to add entries to pop-up menus using the
    insertItem() function, maintaining identifiers for future use; for
    example, to dynamically change menu items.
    In Qt 4, menu entries are completely represented
    by actions for consistency with other user interface components, such as
    toolbar buttons. Create new menus with the QMenu class, and use the
    overloaded QMenu::addAction() functions to insert new entries.
    If you need to manage a set of actions created for a particular menu,
    we suggest that you construct a QActionGroup and add them to that.

    The \l{Qt Examples#Main Windows}{Main Window examples} provided
    show how to use Qt's action system to construct menus, toolbars, and other
    common user interface elements.

    \section1 QPrinter

    The QPrinter class now expects printing to be set up from a
    QPrintDialog.

    \section1 QProcess

    The QProcess class has undergone major improvements in Qt 4. It
    now inherits QIODevice, which makes it possible to combine
    QProcess with a QTextStream or a QDataStream.

    The old \c QProcess class has been renamed Q3Process and moved to
    the Qt3Support library.

    \section1 QProgressBar

    The QProgressBar API has been significantly improved in Qt 4. The
    old \c QProgressBar API is available as Q3ProgressBar in the
    Qt3Support library.

    \section1 QProgressDialog

    The QProgressDialog API has been significantly improved in Qt 4.
    The old \c QProgressDialog API is available as Q3ProgressDialog
    in the Qt3Support library.

    See \l{#properties}{Properties} for a list of QProgressDialog
    properties in Qt 3 that have changed in Qt 4.

    \section1 QPtrCollection<T>

    The \c QPtrCollection<T> abstract base class has been renamed
    Q3PtrCollection<T> moved to the Qt3Support library.
    There is no direct equivalent in Qt 4.

    \omit
    ###
    The QPtrCollection entry is unsatisfactory. The xref is missing
    its list and saying "no direct equivalent" with so suggestions
    seems feeble.
    \endomit

    See \l{Generic Containers} for a list of Qt 4 containers.

    \section1 QPtrDict<T>

    \c QPtrDict<T> and \c QPtrDictIterator<T> have been renamed
    Q3PtrDict<T> and Q3PtrDictIterator<T> and have been moved to the
    Qt3Support library. They have been replaced by the
    more modern QHash<Key, T> and QMultiHash<Key, T> classes and
    their associated iterator classes.

    When porting old code that uses Q3PtrDict<T> to Qt 4, there are
    four classes that you can use:

    \list
    \o QMultiHash<void *, T *>
    \o QMultiHash<void *, T>
    \o QHash<void *, T *>
    \o QHash<void *, T>
    \endlist

    (You can naturally use other types than \c{void *} for the key
    type, e.g. \c{QWidget *}.)

    To port Q3PtrDict<T> to Qt 4, read the \l{#qdict.section}{section
    on QDict<T>}, mentally substituting \c{void *} for QString.

    \target qptrlist.section
    \section1 QPtrList<T>

    QPtrList<T>, QPtrListIterator<T>, and QPtrListStdIterator<T> have
    been moved to the Qt3Support library. They have been
    replaced by the more modern QList and QLinkedList classes and
    their associated iterator classes.

    When porting to Qt 4, you have the choice of using QList<T> or
    QLinkedList<T> as alternatives to QValueList<T>. QList<T> has an
    index-based API and provides very fast random access
    (QList::operator[]), whereas QLinkedList<T> has an iterator-based
    API.

    The following table summarizes the API differences between
    QPtrList<T> and QList<T *>:

    \table
    \header \o QPtrList function \o QList equivalent
    \row \o QPtrList::contains(const T *) \o QList::count(T *)
    \row \o QPtrList::containsRef(const T *) \o QList::count(T *)
    \row \o QPtrList::find(const T *) \o See remark below
    \row \o QPtrList::findRef(const T *) \o See remark below
    \row \o QPtrList::getFirst() \o QList::first()
    \row \o QPtrList::getLast() \o QList::last()
    \row \o QPtrList::inSort(const T *) \o N/A
    \row \o QPtrList::remove(const T *) \o QList::removeAll(T *)
    \row \o QPtrList::remove(uint) \o QList::removeAt(int)
    \row \o QPtrList::removeNode(QLNode *) \o N/A
    \row \o QPtrList::removeRef(const T *) \o QList::removeAll(T *)
    \row \o QPtrList::sort() \o See remark below
    \row \o QPtrList::takeNode(QLNode *) \o N/A
    \row \o QPtrList::toVector(QGVector *) \o See remark below
    \endtable

    Remarks:

    \list 1
    \o  QPtrList::toVector(QGVector *) can be replaced by
        QVector::resize() and qCopy().

        \oldcode
        QPtrList<QWidget> list;
        ...
        QPtrVector<QWidget> vector;
        list.toVector(&vector);
        \newcode
        QList<QWidget *> list;
        ...
        QVector<QWidget *> vector;
        vector.resize(list.size());
        qCopy(list.begin(), list.end(), vector.begin());
        \endcode

    \o  QPtrList::sort() relied on the virtual compareItems() to
        sort items. In Qt 4, you can use \l qSort() instead and pass
        your "compare item" function as an argument.

    \o  QPtrList::find(const T *) returns an iterator, whereas
        QList::indexOf(T *) returns an index. To convert an index
        into an iterator, add the index to QList::begin().

    \o  QPtrList::removeFirst() and QPtrList::removeLast() return a \c
        bool that indicates whether the element was removed or not.
        The corresponding QList functions return \c void. You can
        achieve the same result by calling QList::isEmpty() before
        attempting to remove an item.
    \endlist

    If you use QPtrList's auto-delete feature (by calling
    QPtrList::setAutoDelete(true)), you need to do some more work.
    You have two options: Either you call \c delete yourself whenever
    you remove an item from the container, or you can use QList<T>
    instead of QList<T *> (i.e. store values directly instead of
    pointers to values). Here, we'll see when to call \c delete.

    \omit
    (See \l{What's Wrong with Auto-Delete} for an explanation of why
    the Qt 4 containers don't offer that feature.)
    \endomit

    The following table summarizes the idioms that you need to watch
    out for if you want to call \c delete yourself.

    \table
    \header \o QPtrList idiom \o QList idiom
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 19
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 20
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 21
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 22
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 23
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 24
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 25
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 26
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 27
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 28
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 29
        (removes the current item)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 30
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 31

        (also called from QPtrList's destructor)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 32

        In 99% of cases, the following idiom also works:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 33

        However, it may lead to crashes if \c list is referenced from
        the value type's destructor, because \c list contains
        dangling pointers until clear() is called.
    \endtable

    Be aware that QPtrList's destructor automatically calls clear().
    If you have a QPtrList data member in a custom class and use the
    auto-delete feature, you will need to call \c delete on all the
    items in the container from your class destructor to avoid a
    memory leak.

    QPtrList had the concept of a "current item", which could be used
    for traversing the list without using an iterator. When porting
    to Qt 4, you can use the Java-style QListIterator<T *> (or
    QMutableListIterator<T *>) class instead. The following table
    summarizes the API differences:

    \table
    \header \o QPtrList function \o QListIterator equivalent
    \row \o QPtrList::at() \o N/A
    \row \o QPtrList::current() \o QMutableListIterator::value()
    \row \o QPtrList::currentNode() \o N/A
    \row \o QPtrList::findNext(const T *) \o QListIterator::findNext(const T *)
    \row \o QPtrList::findNextRef(const T *) \o QListIterator::findNext(const T *)
    \row \o QPtrList::first() \o QPtrList::toFront()
    \row \o QPtrList::last() \o QPtrList::toBack()
    \row \o QPtrList::next() \o QPtrList::next()
    \row \o QPtrList::prev() \o QPtrList::previous()
    \row \o QPtrList::remove() \o QMutableListIterator::remove()
    \row \o QPtrList::take() \o QMutableListIterator::remove()
    \endtable

    Be aware that QListIterator has a different way of iterating than
    QPtrList. A typical loop with QPtrList looks like this:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 34

    Here's the equivalent QListIterator loop:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 35

    Finally, QPtrListIterator<T> must also be ported. There are no
    fewer than four iterator classes that can be used as a
    replacement: QList::const_iterator, QList::iterator,
    QListIterator, and QMutableListIterator. The most straightforward
    class to use when porting is QMutableListIterator<T *> (if you
    modify the list through the iterator) or QListIterator<T *> (if
    you don't). The following table summarizes the API differences:

    \table
    \header \o QPtrListIterator function \o Qt 4 equivalent
    \row \o QPtrListIterator::atFirst() \o !QListIterator::hasPrevious() (notice the \c{!})
    \row \o QPtrListIterator::atLast() \o !QListIterator::hasNext() (notice the \c{!})
    \row \o QPtrListIterator::count() \o QList::count() or QList::size()
    \row \o QPtrListIterator::current() \o QMutableListIterator::value()
    \row \o QPtrListIterator::isEmpty() \o QList::isEmpty()
    \row \o QPtrListIterator::toFirst() \o QListIterator::toFront()
    \row \o QPtrListIterator::toLast() \o QListIterator::toBack()
    \row \o QPtrListIterator::operator() \o QMutableListIterator::value()
    \row \o QPtrListIterator::operator*() \o QMutableListIterator::value()
    \endtable

    Again, be aware that QListIterator has a different way of
    iterating than QPtrList. A typical loop with QPtrList looks like
    this:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 36

    Here's the equivalent QListIterator loop:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 37

    Finally, QPtrListStdIterator<T> must also be ported. This is
    easy, because QList also provides STL-style iterators
    (QList::iterator and QList::const_iterator).

    \section1 QPtrQueue<T>

    QPtrQueue has been moved to the Qt3Support library.
    It has been replaced by the more modern QQueue class.

    The following table summarizes the differences between
    QPtrQueue<T> and QQueue<T *>:

    \table
    \header \o QPtrQueue function \o QQueue equivalent
    \row \o QPtrQueue::autoDelete() \o See discussion below
    \row \o QPtrQueue::count() \o QQueue::count() or QQueue::size() (equivalent)
    \row \o QPtrQueue::current() \o QQueue::head()
    \row \o QPtrQueue::remove() \o QQueue::dequeue()
    \row \o QPtrQueue::setAutoDelete() \o See discussion below
    \endtable

    If you use QPtrQueue's auto-delete feature (by calling
    QPtrQueue::setAutoDelete(true)), you need to do some more work.
    You have two options: Either you call \c delete yourself whenever
    you remove an item from the container, or you can use QQueue<T>
    instead of QQueue<T *> (i.e. store values directly instead of
    pointers to values). Here, we will show when to call \c delete.

    \omit
    (See \l{What's Wrong with Auto-Delete} for an explanation of why
    the Qt 4 containers don't offer that feature.)
    \endomit

    \table
    \header \o QPtrQueue idiom \o QQueue idiom
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 38
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 39
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 40
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 41
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 42

        (also called from QPtrQueue's destructor)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 43

        In 99% of cases, the following idiom also works:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 44

        However, it may lead to crashes if \c queue is referenced
        from the value type's destructor, because \c queue contains
        dangling pointers until clear() is called.
    \endtable

    \section1 QPtrStack<T>

    QPtrStack has been moved to the Qt3Support library.
    It has been replaced by the more modern QStack class.

    The following table summarizes the differences between
    QPtrStack<T> and QStack<T *>:

    \table
    \header \o QPtrStack function \o QStack equivalent
    \row \o QPtrStack::autoDelete() \o See discussion below
    \row \o QPtrStack::count() \o QStack::count() or QStack::size() (equivalent)
    \row \o QPtrStack::current() \o QStack::top()
    \row \o QPtrStack::remove() \o QStack::pop()
    \row \o QPtrStack::setAutoDelete() \o See discussion below
    \endtable

    If you use QPtrStack's auto-delete feature (by calling
    QPtrStack::setAutoDelete(true)), you need to do some more work.
    You have two options: Either you call \c delete yourself whenever
    you remove an item from the container, or you can use QStack<T>
    instead of QStack<T *> (i.e. store values directly instead of
    pointers to values). Here, we will show when to call \c delete.

    \omit
    (See \l{What's Wrong with Auto-Delete} for an explanation of why
    the Qt 4 containers don't offer that feature.)
    \endomit

    \table
    \header \o QPtrStack idiom \o QStack idiom
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 45
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 46
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 47
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 48
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 49

        (also called from QPtrStack's destructor)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 50

        In 99% of cases, the following idiom also works:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 51

        However, it may lead to crashes if \c stack is referenced
        from the value type's destructor, because \c stack contains
        dangling pointers until clear() is called.
    \endtable

    \section1 QPtrVector<T>

    QPtrVector<T> has been moved to Qt3Support. It has been replaced
    by the more modern QVector class.

    When porting to Qt 4, you can use QVector<T *> as an alternative
    to QPtrVector<T>. The APIs of QPtrVector<T> and QVector<T *> are
    somewhat similar. The main issue is that QPtrVector supports
    auto-delete whereas QVector doesn't.

    \omit
    (See \l{What's Wrong with Auto-Delete} for an explanation of why
    the Qt 4 containers don't offer that feature.)
    \endomit

    The following table summarizes the API differences between the
    two classes:

    \table
    \header \o QPtrVector function \o QVector equivalent
    \row \o QPtrVector::autoDelete() \o See discussion below
    \row \o QPtrVector::bsearch(const T *) \o \l qBinaryFind()
    \row \o QPtrVector::contains(const T *) \o QVector::count(T *)
    \row \o QPtrVector::containsRef(const T *) \o QVector::count(T *)
    \row \o QPtrVector::count() \o See remark below
    \row \o QPtrVector::insert(uint, T *) \o See remark below
    \row \o QPtrVector::isNull() \o N/A
    \row \o QPtrVector::remove(uint) \o See remark below
    \row \o QPtrVector::setAutoDelete() \o See discussion below
    \row \o QPtrVector::sort() \o \l qSort()
    \row \o QPtrVector::take(uint) \o See remark below
    \row \o QPtrVector::toList(QGList *) \o QList::QList(const QVector &)
    \endtable

    Remarks:

    \list 1
    \o  QPtrVector::insert(uint, T *) sets an item to store a certain
        pointer value. This is \e not the same as QVector::insert(int, T *),
        which creates space for the item by moving following items by
        one position. Use \c{vect[i] = ptr} to set a QVector item to
        a particular value.
    \o  QPtrVector::remove(uint) sets an item to be 0. This is \e not
        the same as QVector::removeAt(int), which entirely erases the
        item, reducing the size of the vector. Use \c{vect[i] = 0} to
        set a QVector item to 0.
    \o  Likewise, QPtrVector::take(uint) sets an item to be 0 and
        returns the previous value of the item. Again, this is easy to
        achieve using QVector::operator[]().
    \o  QPtrVector::count() returns the number of non-null items in
        the vector, whereas QVector::count() (like QVector::size())
        returns the number of items (null or non-null) in the vector.
        Fortunately, it's not too hard to simulate QPtrVector::count().

        \oldcode
        int numValidItems = vect.count();
        \newcode
        int numValidItems = vect.size() - vect.count(0);
        \endcode
    \endlist

    If you use QVector's auto-delete feature (by calling
    QVector::setAutoDelete(true)), you need to do some more work. You
    have two options: Either you call \c delete yourself whenever you
    remove an item from the container, or you use QVector<T> instead
    of QVector<T *> (i.e. store values directly instead of pointers
    to values). Here, we'll see when to call \c delete.

    The following table summarizes the idioms that you need to watch
    out for if you want to call \c delete yourself.

    \table
    \header \o QPtrVector idiom \o QVector idiom
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 52
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 53
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 54
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 55
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 56
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 57
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 58
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 59
    \row
        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 60

        (also called from QPtrVector's destructor)

        \o
        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 61

        In 99% of cases, the following idiom also works:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 62

        However, it may lead to crashes if \c vect is referenced from
        the value type's destructor, because \c vect contains
        dangling pointers until clear() is called.
    \endtable

    Be aware that QPtrVector's destructor automatically calls
    clear(). If you have a QPtrVector data member in a custom class
    and use the auto-delete feature, you will need to call \c delete
    on all the items in the container from your class destructor to
    avoid a memory leak.

    \section1 QPushButton

    See \l{#properties}{Properties} for a list of QPushButton
    properties in Qt 3 that have changed in Qt 4.

    \section1 QRangeControl

    In Qt 3, various "range control" widgets (QDial, QScrollBar,
    QSlider, and QSpin) inherited from both QWidget and
    \c QRangeControl.

    In Qt 4, \c QRangeControl has been replaced with the new
    QAbstractSlider and QAbstractSpinBox classes, which inherit from
    QWidget and provides similar functionality. Apart from eliminating
    unnecessary multiple inheritance, the new design allows
    QAbstractSlider to provide signals, slots, and properties.

    The old \c QRangeControl class has been renamed Q3RangeControl
    and moved to the Qt3Support library, together with
    the (undocumented) \c QSpinWidget class.

    If you use \c QRangeControl as a base class in your application,
    you can switch to use QAbstractSlider or QAbstractSpinBox instead.

    \oldcode
        class VolumeControl : public QWidget, public QRangeControl
        {
            ...
        protected:
            void valueChange() {
                update();
                emit valueChanged(value());
            }
            void rangeChange() {
                update();
            }
            void stepChange() {
                update();
            }
        };
    \newcode
        class VolumeControl : public QAbstractSlider
        {
            ...
        protected:
            void sliderChange(SliderChange change) {
                update();
                if (change == SliderValueChange)
                    emit valueChanged(value());
            }
        };
    \endcode

    \section1 QRegExp

    The search() and searchRev() functions have been renamed to indexIn()
    and lastIndexIn() respectively.

    \section1 QRegion

    The following changes have been made to QRegion in Qt 4:

    \list
    \o  There is no longer any difference between a \e null region and
        an \e empty region. Use isEmpty() in most places where you
        would have used a null QRegion.
    \o  QRegion::rects() used to return a QMemArray<QRect>. It now returns
        a QVector<QRect>.
    \endlist

    \section1 QScrollBar

    See \l{#properties}{Properties} for a list of QScrollBar
    properties in Qt 3 that have changed in Qt 4.

    \section1 QScrollView

    The \c QScrollView class has been renamed Q3ScrollView and moved
    to the Qt3Support library. It has been replaced by
    the QAbstractScrollArea and QScrollArea classes.

    Note that Qt 4 in general uses the QScrollArea::widget() function
    where Qt 3 used QScrollView::viewport(). The rationale for this is
    that it is no longer possible to draw directly on a scroll
    area. The QScrollArea::widget() function returns the widget set on
    the scroll area.

    \c QScrollView was designed to work around the 16-bit limitation
    on widget coordinates found on most window systems. In Qt 4, this
    is done transparently for \e all widgets, so there is no longer a
    need for such functionality in \c QScrollView. For that reason,
    the new QAbstractScrollArea and QScrollArea classes are much more
    lightweight, and concentrate on handling scroll bars.

    \section1 QServerSocket

    The \c QServerSocket class has been renamed Q3ServerSocket and
    moved to the Qt3Support library. In Qt 4, it has been
    replaced by QTcpServer.

    With Q3ServerSocket, connections are accepted by reimplementing a
    virtual function (Q3ServerSocket::newConnection()). With
    QTcpServer, on the other hand, you don't need to subclass.
    Instead, simply connect to the QTcpServer::newConnection()
    signal.

    \section1 QSettings

    The QSettings class has been rewritten to be more robust and to
    respect existing standards (e.g., the INI file format). The API
    has also been extensively revised. The old API is still provided
    when Qt 3 support is enabled.

    Since the format and location of settings have changed between Qt
    3 and Qt 4, the Qt 4 version of your application won't recognize
    settings written using Qt 3.

    \section1 QShared

    The \c QShared class has been obsoleted by the more powerful
    QSharedData and QSharedDataPointer as a means of creating custom
    implicitly shared classes. It has been renamed Q3Shared moved to
    the Qt3Support library.

    An easy way of porting to Qt 4 is to include this class into your
    project and to use it instead of \c QShared:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 63

    If possible, we recommend that you use QSharedData and
    QSharedDataPointer instead. They provide thread-safe reference
    counting and handle all the reference counting behind the scenes,
    eliminating the risks of forgetting to increment or decrement the
    reference count.

    \section1 QSignal

    The QSignal class has been renamed to Q3Signal and moved to the
    Qt3Support library. The preferred approach is to create your own
    QObject subclass with a signal that has the desired signature.
    Alternatively, you can call QMetaObject::invokeMethod() if you
    want to invoke a slot.

    \section1 QSimpleRichText

    QSimpleRichText has been obsoleted by QTextDocument. It has
    bene renamed Q3SimpleRichText and moved to the Qt3Support
    library.

    Previously, you would do the following with Q3SimpleRichText:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 63a

    However, with QTextDocument, you use the following code instead:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 63b

    See \l{Rich Text Processing} for an overview of the Qt 4 rich
    text classes.

    \section1 QSlider

    The QSlider::sliderStart() and QSlider::sliderRect() functions
    have been removed.

    The slider's rect can now be retrieved using the code snippet below:

    \snippet doc/src/snippets/code/doc_src_porting4.qdoc 63c

    In addition, the direction of a vertical QSlider has changed,
    i.e. the bottom is now the minimum, and the top the maximum. You
    can use the QAbstractSlider::invertedAppearance property to
    control this behavior.

    See \l{#properties}{Properties} for a list of QSlider properties
    in Qt 3 that have changed in Qt 4.

    \section1 QSocket

    The \c QSocket class has been renamed Q3Socket and moved to the
    Qt3Support library. In Qt 4, it has been replaced by
    the QTcpSocket class, which inherits most of its functionality
    from QAbstractSocket.

    \section1 QSocketDevice

    The \c QSocketDevice class has been renamed Q3SocketDevice and
    moved to the Qt3Support library. In Qt 4, there is no
    direct equivalent to Q3SocketDevice:

    \list
    \o If you use Q3SocketDevice in a thread to perform blocking network
    I/O (a technique encouraged by the \e{Qt Quarterly} article
    \l{http://doc.trolltech.com/qq/qq09-networkthread.html}{Unblocking Networking}),
    you can now use QTcpSocket, QFtp, or QHttp instead, which can now be used from
    non-GUI threads.

    \o If you use Q3SocketDevice for UDP, you can now use QUdpSocket instead.

    \o If you use Q3SocketDevice for other uses, Qt 4 offers no
    alternative right now. However, there is a \c QAbstractSocketEngine
    internal class that offers a low-level socket API similar to
    Q3SocketDevice. Should the need for such functionality arise in
    Qt 4 applications, we will consider making this class public in a
    future release.
    \endlist

    \section1 QSortedList

    The QSortedList<T> class has been deprecated since Qt 3.0. In Qt
    4, it has been moved to the Qt3Support library.

    In new code, we recommend that you use QList<T> instead and use
    \l qSort() to sort the items.

    \section1 QSplitter

    The function setResizeMode() has been moved into Qt3Support. Set
    the stretch factor in the widget's size policy to get equivalent
    functionality.

    The obsolete function drawSplitter() has been removed. Use
    QStyle::drawPrimitive() to acheive similar functionality.

    \section1 QSpinBox

    See \l{#properties}{Properties} for a list of QSpinBox properties
    in Qt 3 that have changed in Qt 4.

    \section1 QSqlCursor

    The \c QSqlCursor class has been renamed Q3SqlCursor and moved to
    the Qt3Support library. In Qt 4, you can use
    QSqlQuery, QSqlQueryModel, or QSqlTableModel, depending on
    whether you want a low-level or a high-level interface for
    accessing databases.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlDatabase

    QSqlDatabase is now a smart pointer that is passed around by
    value. Simply replace all QSqlDatabase pointers by QSqlDatabase
    objects.

    \section1 QSqlEditorFactory

    The \c QSqlEditorFactory class has been renamed
    Q3SqlEditorFactory and moved to Qt3Support.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlError

    The enum \c{Type} was renamed to \c{ErrorType}, The values were renamed as well:

    \list
    \o None - use NoError instead
    \o Connection - use ConnectionError instead
    \o Statement - use StatementError instead
    \o Transaction - use TransactionError instead
    \o Unknown - use UnknownError instead
    \endlist

    \section1 QSqlFieldInfo

    The QSqlFieldInfo class has been moved to Qt3Support. Its
    functionality is now provided by the QSqlField class.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlForm

    The \c QSqlForm class has been renamed Q3SqlForm and moved to the
    Qt3Support library.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlPropertyMap

    The \c QSqlPropertyMap class has been renamed Q3SqlPropertyMap
    moved to the Qt3Support library.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlQuery

    QSqlQuery::prev() was renamed to QSqlQuery::previous().
    QSqlQuery::prev() remains, but it just calls previous().
    QSqlQuery no longer has any virtual methods, i.e., exec(),
    value(), seek(), next(), prev(), first(), last(), and the
    destructor are no longer virtual.

    \section1 QSqlRecord

    QSqlRecord behaves like a vector now, QSqlRecord::insert() will
    actually insert a new field instead of replacing the existing
    one.

    \section1 QSqlRecordInfo

    The QSqlRecordInfo class has been moved to Qt3Support. Its
    functionality is now provided by the QSqlRecord class.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QSqlSelectCursor

    The \c QSqlSelectCursor class has been renamed Q3SqlSelectCursor
    and moved to the Qt3Support library.

    See \l{QtSql Module} for an overview of the new SQL classes.

    \section1 QStoredDrag

    The \c QStoredDrag class has been renamed Q3StoredDrag and moved
    to the Qt3Support library. In Qt 4, use QMimeData
    instead and call QMimeData::setData() to set the data.

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QStr(I)List

    The QStrList and QStrIList convenience classes have been
    deprecated since Qt 2.0. In Qt 4, they have been moved to the
    Qt3Support library. If you used any of these, we
    recommend that you use QStringList or QList<QByteArray> instead.

    \section1 QStr(I)Vec

    The QStrVec and QStrIVec convenience classes have been deprecated
    since Qt 2.0. In Qt 4, they have been moved to Qt3Support. If you
    used any of these, we recommend that you use QStringList or
    QList<QByteArray> instead.

    \section1 QString

    Here are the main issues to be aware of when porting QString to
    Qt 4:

    \list 1
    \o  The QString::QString(QChar) constructor performed implicit
        conversion in Qt 3. Now, you will need a cast to convert a
        QChar to a QString.

    \o  The QString::QString(const QByteArray &) constructor used to
        stop at the first '\\0' it encountered, for compatibility
        with Qt 1. This quirk has now been fixed; in Qt 4, the
        resulting QString always has the same length as the
        QByteArray that was passed to the constructor.

    \o  The QString::null static constant has been deprecated in Qt
        4. For compatibility, Qt 4 provides a QString::null symbol
        that behaves more or less the same as the old constant. The
        new idiom is to write QString() instead of QString::null, or
        to call clear().

        \oldcode
            str1 = QString::null;
            if (str2 == QString::null)
                do_something(QString::null);
        \newcode
            str1.clear();
            if (str2.isNull())
                do_something(QString());
        \endcode

        In new code, we recommend that you don't rely on the
        distinction between a null string and a (non-null) empty
        string. See \l{Distinction Between Null and Empty Strings}
        for details.

    \o  QString::latin1() and QString::ascii() have been replaced
        with QString::toLatin1() and QString::toAscii(), which return
        a QByteArray instead of a (non-reentrant) \c{const char *}.
        For consistency, QString::utf8() and QString::local8Bit(),
        which already returned a QByteArray (actually a \c QCString),
        have been renamed QString::toUtf8() and
        QString::toLocal8Bit().

        To obtain a \c{const char *} pointer to ASCII or Latin-1 data,
        use QString::toAscii() or QString::toLatin1() to obtain a
        QByteArray containing the data, then call QByteArray::constData()
        to access the character data directly. Note that the pointer
        returned by this function is only valid for the lifetime of the
        byte array; you should avoid taking a pointer to the data
        contained in temporary objects.

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 64

        In the above example, the \c goodData pointer is valid for the lifetime
        of the \c asciiData byte array. If you need to keep a copy of the data
        in a non-Qt data structure, use standard C memory allocation and string
        copying functions to do so \e before destroying the byte array.

    \o  QString::at() returned a non-const reference, whereas the
        new QString::at() returns a const value. Code like

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 65

        will no longer compile. Instead, use QString::operator[]:

        \snippet doc/src/snippets/code/doc_src_porting4.qdoc 66

    \o  The QString::contains(\e x) function (where \e x is a
        character or a string) has been renamed QString::count(\e x).
        In addition, there now exists a set of QString::contains()
        functions that returns a boolean value. Replace old calls to
        contains() with either count() or contains(), depending on
        whether you care about the specific number of occurrences of
        a character in the string or only care about whether the
        string contains that character or not.

    \o  Many functions in QString had a \c bool parameter that
        specified case sensitivity. In Qt 4, in the interest of code
        readability and maintainability, the \c bool parameters have
        been replaced by the Qt::CaseSensitivity enum, which can take
        the values Qt::CaseSensitive and Qt::CaseInsensitive.

        \oldcode
            if (url.startsWith("http:", false))
                ...
        \newcode
            if (url.startsWith("http:", Qt::CaseInsensitive))
                ...
        \endcode

    \o  The QString::setExpand(uint, QChar) function, which already
        was obsolete in Qt 3, is no longer available. Use
        QString::operator[] instead.

        \oldcode
            str.setExpand(32, '$');
        \newcode
            str[32] = '$';
        \endcode

    \o  The \c QT_NO_ASCII_CAST and \c QT_NO_CAST_ASCII macros have
        been renamed \c QT_NO_CAST_TO_ASCII and \c
        QT_NO_CAST_FROM_ASCII, respectively.

    \o  The QString::data() used to return the same as
        QString::ascii(). It now returns a pointer to the Unicode
        data stored in the QString object. Call QString::ascii() if
        you want the old behavior.

    \o  QString::arg() now converts two-digit place markers, allowing
        up to 99 place markers to be used in any given string.

    \o  Comparisons between QStrings and \c NULL in order to determine
        whether strings are empty are no longer allowed.
        Use \l{QString::}{isEmpty()} instead.

    \endlist

    \section1 QStringList

    QStringList now inherits from QList<QString> and can no longer be
    converted to a QValueList<QString>. Since QValueList inherits QList a
    cast will work as expected.

    This change implies some API incompatibilities for QStringList.
    For example, at() returns the string, not an iterator. See the
    \l{#qvaluelist.section}{section on QValueList} for details.

    The static QStringList::split() function for splitting strings into
    lists of smaller strings has been replaced by QString::split(),
    which returns a QStringList.

    \section1 QStyle

    The QStyle API has been overhauled and improved. Most of the information on
    why this change was done is described in \l{The Qt 4 Style API}{the QStyle overview}.

    Since QStyle is mostly used internally by Qt's widgets and styles and since
    it is not essential to the good functioning of an application, there is no
    compatibility path. This means that we have changed many enums and
    functions and the qt3to4 porting tool will not change much in your qstyle
    code. To ease the pain, we list some of the major changes here.

    QStyleOption has taken on a more central role and is no longer an optional
    argument, please see the QStyleOption documentation for more information.

    The QStyle::StyleFlags have been renamed QStyle::StateFlags and are now prefixed State_
    instead of Style_, in addition the Style_ButtonDefault flag has moved to
    QStyleOptionButton.

    The QStyle::PrimitiveElement enumeration has undergone extensive change.
    Some of the enums were moved to QStyle::ControlElement, some were removed
    and all were renamed. This renaming is not done by the qt3to4 porting tool,
    so you must do it yourself. The table below shows how things look
    now.

    \table
    \header \o Old name \o New name \o Remark
    \row \o \c PE_ButtonCommand             \o QStyle::PE_PanelButtonCommand
    \row \o \c PE_ButtonDefault             \o QStyle::PE_FrameDefaultButton
    \row \o \c PE_ButtonBevel               \o QStyle::PE_PanelButtonBevel
    \row \o \c PE_ButtonTool                \o QStyle::PE_PanelButtonTool
    \row \o \c PE_ButtonDropDown            \o QStyle::PE_IndicatorButtonDropDown
    \row \o \c PE_FocusRect                 \o QStyle::PE_FrameFocusRect
    \row \o \c PE_ArrowUp                   \o QStyle::PE_IndicatorArrowUp
    \row \o \c PE_ArrowDown                 \o QStyle::PE_IndicatorArrowDown
    \row \o \c PE_ArrowRight                \o QStyle::PE_IndicatorArrowRight
    \row \o \c PE_ArrowLeft                 \o QStyle::PE_IndicatorArrowLeft
    \row \o \c PE_SpinBoxUp                 \o QStyle::PE_IndicatorSpinUp
    \row \o \c PE_SpinBoxDown               \o QStyle::PE_IndicatorSpinDown
    \row \o \c PE_SpinBoxPlus               \o QStyle::PE_IndicatorSpinPlus
    \row \o \c PE_SpinBoxMinus              \o QStyle::PE_IndicatorSpinMinus
    \row \o \c PE_SpinBoxSlider             \o QStyle::CE_SpinBoxSlider \o uses QStyle::drawControl()
    \row \o \c PE_Indicator                 \o QStyle::PE_IndicatorCheckBox
    \row \o \c PE_IndicatorMask             \o N/A \o use QStyle::styleHint() to retrieve mask
    \row \o \c PE_ExclusiveIndicator        \o QStyle::PE_IndicatorRadioButton
    \row \o \c PE_ExclusiveIndicatorMask    \o N/A \o use QStyle::styleHint() to retrieve mask
    \row \o \c PE_DockWindowHandle          \o QStyle::PE_IndicatorToolBarHandle
    \row \o \c PE_DockWindowSeparator       \o QStyle::PE_Q3DockWindowSeparator
    \row \o \c PE_DockWindowResizeHandle    \o QStyle::PE_IndicatorDockWindowResizeHandle
    \row \o \c PE_DockWindowTitle           \o QStyle::CE_DockWindowTitle \o uses QStyle::drawControl()
    \row \o \c PE_Splitter                  \o QStyle::CE_Splitter \o uses QStyle::drawControl()
    \row \o \c PE_Panel                     \o QStyle::PE_Frame
    \row \o \c PE_PanelMenu                 \o QStyle::PE_FrameMenu
    \row \o \c PE_PanelMenuBar              \o QStyle::PE_PanelMenuBar
    \row \o \c PE_PanelDockWindow           \o QStyle::PE_FrameDockWindow
    \row \o \c PE_TabBarBase                \o QStyle::PE_FrameTabBarBase
    \row \o \c PE_HeaderSection             \o QStyle::CE_HeaderSection \o uses QStyle::drawControl()
    \row \o \c PE_HeaderArrow               \o QStyle::PE_IndicatorHeaderArrow
    \row \o \c PE_StatusBarSection          \o QStyle::PE_FrameStatusBar
    \row \o \c PE_Separator                 \o QStyle::PE_Q3Separator
    \row \o \c PE_SizeGrip                  \o QStyle::CE_SizeGrip \o uses QStyle::drawControl()
    \row \o \c PE_CheckMark                 \o QStyle::PE_IndicatorMenuCheckMark
    \row \o \c PE_ScrollBarAddLine          \o QStyle::CE_ScrollBarAddLine \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarSubLine          \o QStyle::CE_ScrollBarSubLine \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarAddPage          \o QStyle::CE_ScrollBarAddPage \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarSubPage          \o QStyle::CE_ScrollBarSubPage \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarSlider           \o QStyle::CE_ScrollBarSlider  \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarFirst            \o QStyle::CE_ScrollBarFirst   \o uses QStyle::drawControl()
    \row \o \c PE_ScrollBarLast             \o QStyle::CE_ScrollBarLast    \o uses QStyle::drawControl()
    \row \o \c PE_ProgressBarChunk          \o QStyle::PE_IndicatorProgressChunk
    \row \o \c PE_PanelLineEdit             \o QStyle::PE_FrameLineEdit
    \row \o \c PE_PanelTabWidget            \o QStyle::PE_FrameTabWidget
    \row \o \c PE_WindowFrame               \o QStyle::PE_FrameWindow
    \row \o \c PE_CheckListController       \o QStyle::PE_Q3CheckListController
    \row \o \c PE_CheckListIndicator        \o QStyle::PE_Q3CheckListIndicator
    \row \o \c PE_CheckListExclusiveIndicato\o QStyle::PE_Q3CheckListExclusiveIndicator
    \row \o \c PE_PanelGroupBox             \o QStyle::PE_FrameGroupBox
    \row \o \c PE_TreeBranch                \o QStyle::PE_IndicatorBranch
    \row \o \c PE_RubberBand                \o QStyle::CE_RubberBand \o uses QStyle::drawControl()
    \row \o \c PE_PanelToolBar              \o QStyle::PE_PanelToolBar
    \row \o \c PE_ToolBarHandle             \o QStyle::PE_IndicatorToolBarHandle
    \row \o \c PE_ToolBarSeparator          \o QStyle::PE_IndicatorToolBarSeparator
    \endtable

    The QStyle::drawControlMask() and QStyle::drawComplexControlMask()
    functions have been removed. They are replaced with a style hint.

    The QStyle::drawItem() overloads that took both a pixmap and a string have
    been removed. Use QStyle::drawItemText() and QStyle::drawItemPixmap() directly.

    The QStyle::itemRect() overload that took both a pixmap and a string is also removed, use
    either QStyle::itemTextRect() or QStyle::itemPixmapRect() instead.

    \section1 QStyleSheet

    The QStyleSheet and QStyleSheetItem classes have been renamed
    Q3StyleSheet and Q3StyleSheetItem, and have been moved to the
    Qt3Support library.

    See \l{Rich Text Processing} for an overview of the Qt 4 rich
    text classes, and \l{Qt Style Sheets} for a description of
    CSS-like style sheet support in Qt 4.2 and above.

    \section1 QSyntaxHighlighter

    The \c QSyntaxHighlighter class from Qt 3 has been renamed
    Q3SyntaxHighlighter and moved to the Qt3Support library. Since Qt
    4.1, it has been replaced by a new QSyntaxHighlighter class based
    on Qt 4's new rich text engine.

    \section1 QTabBar

    See \l{#properties}{Properties} for a list of QTabBar properties
    in Qt 3 that have changed in Qt 4.

    \section1 QTabDialog

    The \c QTabDialog class is no longer part of the public Qt API.
    It has been renamed Q3TabDialog and moved to Qt3Support. In Qt 4
    applications, you can easily obtain the same result by combining
    a QTabWidget with a QDialog and provide \l{QPushButton}s
    yourself.

    See also the \l{dialogs/tabdialog} example, which shows how to
    implement tab dialogs in Qt 4.

    \section1 QTabWidget

    See \l{#properties}{Properties} for a list of QTabWidget
    properties in Qt 3 that have changed in Qt 4.

    \section1 QTable

    The \c QTable, \c QTableItem, \c QComboTableItem, \c
    QCheckTableItem, and \c QTableSelection classes have been renamed
    Q3Table, Q3TableItem, Q3ComboTableItem, Q3CheckTableItem, and
    Q3TableSelection and moved to the Qt3Support library.
    New Qt applications should use the new QTableWidget or QTableView
    class instead.

    Some of these classes behave differently with respect to the way
    they handle \c NULL pointers. For example, Q3TableItem::setPixmap()
    no longer accepts \c NULL or 0 to indicate that the item should
    contain a null pixmap; in this case, a null pixmap should be
    constructed and passed explicitly to the function.

    See \l{Model/View Programming} for an overview of the new item
    view classes.

    \section1 QTextCodec

    The loadCharmap() and loadCharmapFromFile() functions are no longer
    available in Qt 4. You need to create your own codec if you want to
    create a codec based on a POSIX2 charmap definition.

    \section1 QTextDrag

    The \c QTextDrag class has been renamed Q3TextDrag and moved to
    the Qt3Support library. In Qt 4, use QMimeData
    instead and call QMimeData::setText() to set the data.

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QTextEdit

    The old QTextEdit and QTextBrowser classes have been renamed
    Q3TextEdit and Q3TextBrowser, and have been moved to Qt3Support.
    The new QTextEdit and QTextBrowser have a somewhat different API.

    The \c QTextEdit::setWrapPolicy() function has been renamed to \l{QTextEdit::setWordWrapMode()}{setWordWrapMode()} and the
    \c QTextEdit::setWrapColumnOrWidth() function has been renamed to \l{QTextEdit::setLineWrapColumnOrWidth()}
    {setLineWrapColumnOrWidth()}. The Q3TextEdit::setWrapPolicy() and Q3TextEdit::setWrapColumnOrWidth() still provide this
    functionality in the Q3TextEdit class.


    See \l{Rich Text Processing} for an overview of the Qt 4 rich
    text classes.

    \section1 QTextIStream

    The QTextIStream convenience class is no longer provided in Qt 4. Use
    QTextStream directly instead.

    \section1 QTextOStream

    The QTextOStream convenience class is no longer provided in Qt 4. Use
    QTextStream directly instead.

    \section1 QTextOStreamIterator

    The undocumented \c QTextOStreamIterator class has been removed
    from the Qt library. If you need it in your application, feel
    free to copy the source code from the Qt 3 \c <qtl.h> header
    file.

    \section1 QTextStream

    QTextStream has undergone a number of API and implementation enhancements,
    and some of the changes affect QTextStream's behavior:

    \list
    \o QTextStream now uses buffered writing, which means that you need to
       call QTextStream::flush(), or use the streaming manipulators \c endl or
       \c flush if you need QTextStream to flush its write buffer. The stream is
       flushed automatically if QTextStream is deleted or when the device is
       closed.
    \o QTextStream now uses buffered reading, so if you read a line from the
       stream, QTextStream will read as much as it can from the device to
       fill up its internal read buffer. This speeds up reading significantly,
       but Qt 3 code that mixed QTextStream access and direct device access
       may need to be updated.
    \o While QTextStream in Qt 3 always translated end-of-line characters from
       Windows style ("\\r\\n") to Unix style ("\\n") on Windows, QTextStream in
       Qt 4 only does this on devices opened with the \c{QIODevice::Text} mode
       (formerly \c{IO_Translate}).
    \endlist

    Note that when using a QTextStream on a QFile in Qt 4, calling
    QIODevice::reset() on the QFile will not have the expected result
    because QTextStream now buffers the file. Use the
    QTextStream::seek() function instead.

    \section1 QTextView

    The \c QTextView class has been renamed Q3TextView and moved to the
    Qt3Support library.

    \section1 QTimeEdit

    The QTimeEdit class in Qt 4 is a convenience class based on
    QDateTimeEdit. The old class has been renamed Q3TimeEdit and moved
    to the Qt3Support library.

    See \l{Porting to Qt 4 - Virtual Functions}{Virtual Functions} for
    a list of \c QTimeEdit virtual member functions in Qt 3 that are no
    longer virtual in Qt 4.

    \section1 QTimer

    Windows restricts the granularity of timers, but starting with Qt 4,
    we emulate a finer time resolution. On Windows XP we use the
    multimedia timer API, which gives us 1 millisecond resolution for
    QTimer.

    Note that other versions of Windows have a lower timer resolution,
    and that code relying on underlying system timer restrictions
    encounters no such limitations using Qt 4 (e.g., setting an
    interval of 0 millisecond results in Qt occupying all of the
    processor time when no GUI events need processing).

    \section1 QToolBar

    The old \c QToolBar class, which worked with the old \c
    QMainWindow and \c QDockArea classes and inherited from \c
    QDockWindow, has been renamed Q3ToolBar and moved to
    Qt3Support. Note that, when using Q3ToolBar, the toolbar's actions
    must be \l {Q3Action}s.

    Use the new QToolBar class in new applications.

    \note \l{Q3ToolBar}'s
    \l{Q3DockWindow::setHorizontallyStretchable()}{horizontallyStretchable}
    property can be achieved in QToolBar with
    \l{QWidget#Size Hints and Size Policies}{size policies}.

    \section1 QToolButton

    See \l{#properties}{Properties} for a list of QToolButton properties
    in Qt 3 that have changed in Qt 4.

    Note that many of the properties that could previously be set in
    the constructor must now be set separately.

    \section1 QToolTip

    The QToolTip::setGloballyEnabled() function no longer exists.
    Tooltips can be disabled by \l{QObject::installEventFilter()}{installing
    an event filter} on qApp (the unique QApplication object) to block events
    of type QEvent::ToolTip.

    \section1 QUriDrag

    The \c QUriDrag class has been renamed Q3UriDrag and moved to the
    Qt3Support library. In Qt 4, use QMimeData instead
    and call QMimeData::setUrl() to set the URL.

    See \l{Porting to Qt 4 - Drag and Drop} for a comparison between
    the drag and drop APIs in Qt 3 and Qt 4.

    \section1 QUrl

    The QUrl class has been rewritten from scratch in Qt 4 to be more
    standard-compliant. The old QUrl class has been renamed Q3Url and
    moved to the Qt3Support library.

    The new QUrl class provides an extensive list of compatibility
    functions to ease porting from Q3Url to QUrl. A few functions
    require you to change your code:

    \list
    \o Q3Url::Q3Url(const Q3Url &, const QString &, bool) can be
       simulated by combining the URLs manually (using
       QString::operator+(), for example).
    \o Q3Url::setEncodedPathAndQuery(const QString &) is replaced by
       QUrl::setPath() and QUrl::setEncodedQuery().
    \o Q3Url::encodedPathAndQuery() is replaced by QUrl::path() and
       QUrl::encodedQuery().
    \o Q3Url::isLocalFile() can be simulated by checking that
       QUrl::protocol() is "file".
    \o Q3Url::toString(bool, bool) is replaced by
       QUrl::toString(int), where the \c int parameter specifies a
       combination of \l{QUrl::FormattingOptions}{formatting
       options}.
    \endlist

    \section1 QUrlOperator

    The \c QUrlOperator class is no longer part of the public Qt API.
    It has been renamed Q3UrlOperator and moved to Qt3Support.

    From Qt 4.4, the Network Access API provides a subset of the features
    provided by \c QUrlOperator that are mostly intended for use with
    applications that use the HTTP and FTP protocols. See the
    QNetworkRequest, QNetworkReply, and QNetworkAccessManager documentation
    for further details.

    \target qvaluelist.section
    \section1 QValueList<T>

    The QValueList<T> class has been replaced by QList<T> and
    QLinkedList<T> in Qt 4. As a help when porting older Qt
    applications, the Qt3Support library contains a
    QValueList<T> class implemented in terms of the new
    QLinkedList<T>. Similarly, it contains QValueListIterator<T> and
    QValueListConstIterator<T> classes implemented in terms of
    QLinkedList<T>::iterator and QLinkedList<T>::const_iterator.

    When porting to Qt 4, you have the choice of using QList<T> or
    QLinkedList<T> as alternatives to QValueList<T>. QList<T> has an
    index-based API and provides very fast random access
    (QList::operator[]), whereas QLinkedList<T> has an iterator-based
    API.

    Here's a list of problem functions:

    \list
    \o  QValueList(const std::list<T> &) doesn't exist in QList or
        QLinkedList. You can simulate it by calling
        \l{QLinkedList::append()}{append()} in a loop.

    \o  QValueList::insert(iterator, size_type, const T& x) doesn't
        exist in QList or QLinkedList. Call
        \l{QLinkedList::insert()}{insert()} repeatedly instead.

    \o  QValueList::fromLast() doesn't exist in QList or QLinkedList. Use
        QValueList::end() instead.

        \oldcode
        for (QValueList<T>::iterator i = list.fromLast(); i != list.begin(); --i)
            do_something(*i);
        \newcode
        QLinkedList<T>::iterator i = list.end();
        while (i != list.begin()) {
            --i; // decrement i before using it
            do_something(*i);
        }
        \endcode

    \o  QValueList::append() and QValueList::prepend() return an
        iterator to the inserted item. QList's and QLinkedList's
        corresponding functions don't, but it's not a problem because
        QValueList::prepend() always returns begin() and append()
        always returns QValueList::end() - 1.

    \o  QValueList::at(\e i) return an iterator to the item at index
        \e i. This corresponds to QList::begin() + \e i.

    \o  QValueList::contains(const T &) corresponds to
        QList::count(const T &) and QLinkedList::count(const T &).
    \endlist

    \section1 QValueVector<T>

    The QValueVector<T> class has been replaced by QVector<T> in Qt
    4. As a help when porting older Qt applications, the Qt3Support
    library contains a Q3ValueVector<T> class implemented in terms of
    the new QVector<T>.

    When porting from QValueVector<T> to QVector<T>, you might run
    into the following incompatibilities:

    \list
    \o QValueVector(const std::vector<T> &) doesn't exist in QVector.
       You can simulate it by calling QVector::append()} in a loop.
    \o QValueVector::resize(int, const T &) doesn't exist in QVector.
       If you want the new items to be initialized with a particular
       value, use QVector::insert() instead.
    \o QValueVector::at() on a non-const vector returns a non-const
       reference. This corresponds to QVector::operator[]().
    \o Both QValueVector::at() functions have an \e ok parameter of
       type \c{bool *} that is set to true if the index is within
       bounds. This functionality doesn't exist in QVector; instead,
       check the index against QVector::size() yourself.
    \endlist

    See \l{Generic Containers} for an overview of the Qt 4 container
    classes.

    \section1 QVariant

    Some changes to the rest of the Qt library have
    implications on QVariant:

    \list 1
    \o The \c QVariant::ColorGroup enum value is defined only
       if \c QT3_SUPPORT is defined.
    \o The \c QVariant::IconSet enum value has been renamed
       QVariant::Icon.
    \o The \c QVariant::CString enum value is now a synonym for
       QVariant::ByteArray.
    \endlist

    Also, the QVariant(bool, int) constructor has been replaced by QVariant(bool).
    Old code like QVariant(true, 0) should be replaced with QVariant(true); otherwise,
    the QVariant(int, void *) overload might accidentally be triggered.

    Many of QVariant's convenience functions in Qt 3, such as toColor() and
    toKeySequence(), have been removed to enable QVariant to be part of the
    QtCore module. QVariant is still able to hold values of these types.

    Types which are not supported by any of the QVariant constructors can be
    stored as variants with the QVariant::fromValue() function. Types with no
    suitable convenience function for unpacking can be retrieved with the
    QVariant::value() function or passed directly to classes that implement
    the QVariant() operator.

    \table
    \header \o Qt 3 function \o Qt 4 function
    \input porting4-removedvariantfunctions.qdocinc
    \endtable

    See the QVariant::Type enum for a list of types supported by QVariant.

    \section1 QVBox

    The \c QVBox class is now only available as Q3VBox in Qt 4. You
    can achieve the same result as \c QVBox by creating a QWidget
    with a vertical layout:

    \oldcode
    QVBox *vbox = new QVBox;
    QPushButton *child1 = new QPushButton(vbox);
    QPushButton *child2 = new QPushButton(vbox);
    \newcode
    QWidget *vbox = new QWidget;
    QPushButton *child1 = new QPushButton;
    QPushButton *child2 = new QPushButton;

    QVBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(child1);
    layout->addWidget(child2);
    vbox->setLayout(layout);
    \endcode

    Note that child widgets are not automatically placed into the widget's
    layout; you will need to manually add each widget to the QVBoxLayout.

    \section1 QVGroupBox

    The \c QVGroupBox class has been renamed Q3VGroupBox and moved to
    the Qt3Support library.
    Qt 4 does not provide a specific replacement class for \c QVGroupBox
    since QGroupBox is designed to be a generic container widget. As a
    result, you need to supply your own layout for any child widgets.

    See \l{#QGroupBox} for more information about porting code that uses
    group boxes.

    \section1 QWhatsThis

    The QWhatsThis class has been redesigned in Qt 4. The old \c
    QWhatsThis class is available as Q3WhatsThis in Qt3Support.

    \section1 QWidget

    Widget background painting has been greatly improved, supporting
    flicker-free updates and making it possible to have
    semi-transparent widgets. This renders the following background
    handling functions obsolete:

    \list
    \o QWidget::repaint(bool noErase) - the \c noErase boolean parameter is gone
    \o QWidget::setBackgroundMode(BackgroundMode m)
    \o QWidget::backgroundBrush() const
    \o QWidget::setBackgroundPixmap(const QPixmap &pm)
    \o QWidget::backgroundPixmap() const
    \o QWidget::setBackgroundColor(const QColor &c)
    \o QWidget::backgroundColor() const
    \o QWidget::foregroundColor() const
    \o QWidget::eraseColor() const
    \o QWidget::setEraseColor(const QColor &c)
    \o QWidget::erasePixmap() const
    \o QWidget::setErasePixmap(const QPixmap &p)
    \o QWidget::paletteForegroundColor()
    \o QWidget::setPaletteForegroundColor(const QColor &c)
    \o QWidget::paletteBackgroundColor()
    \o QWidget::setPaletteBackgroundColor(const QColor &c)
    \o QWidget::paletteBackgroundPixmap() const
    \o QWidget::setPaletteBackgroundPixmap(const QPixmap &p)
    \o QWidget::erase()
    \o QWidget::erase(const QRect &r)
    \o QWidget::setBackgroundOrigin( BackgroundOrigin )
    \o QWidget::BackgroundOrigin backgroundOrigin() const
    \o QWidget::backgroundOffset()
    \endlist

    Sample code on how to do obtain similar behavior from Qt 4, previously
    handled by some of the above functions can be found in the
    \l{http://doc.trolltech.com/qwidget-qt3.html}{Qt 3 Support Members for QWidget}
    page.

    A widget now receives change events in its QWidget::changeEvent()
    handler. This makes the following virtual change handlers obsolete:

    \list
    \o QWidget::styleChange - use QEvent::StyleChange
    \o QWidget::enabledChange - use QEvent::EnabledChange
    \o QWidget::paletteChange - use QEvent::PaletteChange
    \o QWidget::fontChange - use QEvent::FontChange
    \o QWidget::windowActivationChange - use QEvent::ActivationChange
    \o QWidget::languageChange - use QEvent::LanguageChange
    \endlist

    The following functions were slots, but are no more:
    \list
    \o QWidget::clearFocus()
    \o QWidget::setMouseTracking()
    \o QWidget::stackUnder(QWidget*)
    \o QWidget::move(int x, int y)
    \o QWidget::move(const QPoint &)
    \o QWidget::resize(int w, int h)
    \o QWidget::resize(const QSize &)
    \o QWidget::setGeometry(int x, int y, int w, int h)
    \o QWidget::setGeometry(const QRect &)
    \o QWidget::adjustSize()
    \o QWidget::update(int x, int y, int w, int h)
    \o QWidget::update(const QRect&)
    \o QWidget::repaint(bool erase)
    \o QWidget::repaint(int x, int y, int w, int h, bool erase)
    \o QWidget::repaint(const QRect &, bool erase)
    \o QWidget::repaint(const QRegion &, bool erase)
    \o QWidget::setCaption(const QString &)
    \o QWidget::setIcon(const QPixmap &)
    \o QWidget::setIconText(const QString &)
    \endlist

    The following functions were incorrectly marked as virtual:

    \list
    \o QWidget::close(bool alsoDelete)
    \o QWidget::create(WId, bool, bool)
    \o QWidget::destroy(bool)
    \o QWidget::move(int x, int y)
    \o QWidget::reparent(QWidget *parent, WFlags, const QPoint &, bool)
    \o QWidget::resize(int w, int h)
    \o QWidget::setAcceptDrops(bool on)
    \o QWidget::setActiveWindow()
    \o QWidget::setAutoMask(bool)
    \o QWidget::setBackgroundColor(const QColor &)
    \o QWidget::setBackgroundMode(BackgroundMode)
    \o QWidget::setBackgroundOrigin(BackgroundOrigin)
    \o QWidget::setBackgroundPixmap(const QPixmap &)
    \o QWidget::setCaption(const QString &)
    \o QWidget::setCursor(const QCursor &)
    \o QWidget::setEnabled(bool)
    \o QWidget::setEraseColor(const QColor &)
    \o QWidget::setErasePixmap(const QPixmap &)
    \o QWidget::setFocus()
    \o QWidget::setFocusPolicy(FocusPolicy)
    \o QWidget::setFocusProxy(QWidget *)
    \o QWidget::setFont(const QFont &)
    \o QWidget::setGeometry(const QRect &)
    \o QWidget::setGeometry(int x, int y, int w, int h)
    \o QWidget::setIcon(const QPixmap &)
    \o QWidget::setIconText(const QString &)
    \o QWidget::setKeyCompression(bool)
    \o QWidget::setMask(const QBitmap &)
    \o QWidget::setMask(const QRegion &)
    \o QWidget::setMaximumSize(int maxw, int maxh)
    \o QWidget::setMicroFocusHint(int x, int y, int w, int h, bool, QFont *f)
    \o QWidget::setMinimumSize(int minw, int minh)
    \o QWidget::setMouseTracking(bool enable)
    \o QWidget::setPalette(const QPalette &)
    \o QWidget::setPaletteBackgroundColor(const QColor &)
    \o QWidget::setPaletteBackgroundPixmap(const QPixmap &)
    \o QWidget::setSizeIncrement(int w, int h)
    \o QWidget::setSizePolicy(QSizePolicy)
    \o QWidget::setUpdatesEnabled(bool enable)
    \o QWidget::setWState(uint)
    \o QWidget::show()
    \o QWidget::showFullScreen()
    \o QWidget::showMaximized()
    \o QWidget::showMinimized()
    \o QWidget::showNormal()
    \o QWidget::sizePolicy()
    \o QWidget::unsetCursor()
    \endlist

    The internal clearWState() function was removed. Use
    QWidget::setAttribute() instead.

    setWFlags() was renamed QWidget::setWindowFlags().

    clearWFlags() has no direct replacement. You can use
    QWidget::setAttribute() instead. For example,
    \c{setAttribute(..., false)} to clear an attribute. More information
    is available \l{http://doc.trolltech.com/qwidget.html#setAttribute}{here}.

    testWFlags() was renamed to \l{QWidget::testAttribute()}{testAttribute()}.

    See \l{#properties}{Properties} for a list of QWidget properties
    in Qt 3 that have changed in Qt 4.

    \section1 QWidgetFactory

    The \c QWidgetFactory class has been replaced by QFormBuilder in Qt 4.

    \section1 QWidgetIntDict

    The QWidgetIntDict class was a synonym for QIntDict<QWidget>. It
    is no longer available in Qt 4. If you link against Qt3Support,
    you can use Q3IntDict<QWidget> instead; otherwise, see the
    \l{#qdict.section}{section on QDict<T>}.

    \target qwidgetlist.section
    \section1 QWidgetList

    In Qt 3, the QWidgetList class was a typedef for
    QPtrList<QWidget>. In Qt 4, it is a typedef for QList<QWidget *>.
    See the \l{#qptrlist.section}{section on QPtrList<T>}.

    \section1 QWidgetPlugin

    The QWidgetPlugin class is no longer available in Qt 4. To create
    custom widget plugins, subclass QDesignerCustomWidgetInterface to
    provide information about the custom widget, and build a plugin in
    the way described in the \l{designer/customwidgetplugin}{Custom
    Widget Plugin} example.

    \section1 QWidgetStack

    The QWidgetStack class is no longer part of the Qt public API. It
    has been renamed Q3WidgetStack and moved to Qt3Support. In Qt 4
    applications, you can use QStackedWidget instead to obtain the
    same results.

    \section1 QWizard

    The \c QWizard class was reintroduced in Qt 4.3. See the
    \l{Trivial Wizard Example}, \l{License Wizard Example} and
    \l{Class Wizard Example} for more details.

    \section1 QWorkspace

    The \c QWorkspace in Qt 4 class requires explicit adding of MDI
    windows with QWorkspace::addWindow().
*/

/*!
    \page porting4-virtual-functions.html
    \title Porting to Qt 4 - Virtual Functions
    \contentspage {Porting Guides}{Contents}
    \previouspage Porting to Qt 4
    \nextpage Porting to Qt 4 - Drag and Drop
    \ingroup porting
    \brief An overview of changes to virtual functions in Qt 4.

    \section1 Virtual Functions

    Virtual functions that changed their signature in Qt 4:

    \table
    \header \o Qt 3 function signature \o Qt 4 function signature
    \input porting4-modifiedvirtual.qdocinc
    \endtable

    Virtual functions that are not virtual in Qt 4:

    \table
    \header \o Qt 3 function \o Comment
    \input porting4-removedvirtual.qdocinc
    \endtable
*/
