Doc: Use the \nullptr macro instead of 0

This enables overriding the macro so that it translates
to 'None' in the Qt for Python context.

Change-Id: Ib3cecf57eeb0405a1929309b71e9f012a07f11cf
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>

src/corelib/animation/qabstractanimation.cpp

@@ -1083,7 +1083,7 @@ QAbstractAnimation::State QAbstractAnimation::state() const
 
 /*!
     If this animation is part of a QAnimationGroup, this function returns a
-    pointer to the group; otherwise, it returns 0.
+    pointer to the group; otherwise, it returns \nullptr.
 
     \sa QAnimationGroup::addAnimation()
 */

src/corelib/codecs/qtextcodec.cpp

@@ -1244,7 +1244,7 @@ QTextCodec *QTextCodec::codecForUtfText(const QByteArray &ba)
     \obsolete
 
     Returns the codec used by QObject::tr() on its argument. If this
-    function returns 0 (the default), tr() assumes Latin-1.
+    function returns \nullptr (the default), tr() assumes Latin-1.
 */
 
 /*!

src/corelib/kernel/qabstracteventdispatcher.cpp

@@ -162,7 +162,7 @@ QAbstractEventDispatcher::~QAbstractEventDispatcher()
     Returns a pointer to the event dispatcher object for the specified
     \a thread. If \a thread is zero, the current thread is used. If no
     event dispatcher exists for the specified thread, this function
-    returns 0.
+    returns \nullptr.
 
     \b{Note:} If Qt is built without thread support, the \a thread
     argument is ignored.

src/corelib/kernel/qcoreapplication.cpp

@@ -2923,7 +2923,7 @@ bool QCoreApplication::hasPendingEvents()
 
 /*!
     Returns a pointer to the event dispatcher object for the main thread. If no
-    event dispatcher exists for the thread, this function returns 0.
+    event dispatcher exists for the thread, this function returns \nullptr.
 */
 QAbstractEventDispatcher *QCoreApplication::eventDispatcher()
 {

src/corelib/kernel/qmetaobject.cpp

@@ -349,7 +349,7 @@ bool QMetaObject::inherits(const QMetaObject *metaObject) const Q_DECL_NOEXCEPT
     \internal
 
     Returns \a obj if object \a obj inherits from this
-    meta-object; otherwise returns 0.
+    meta-object; otherwise returns \nullptr.
 */
 QObject *QMetaObject::cast(QObject *obj) const
 {
@@ -361,7 +361,7 @@ QObject *QMetaObject::cast(QObject *obj) const
     \internal
 
     Returns \a obj if object \a obj inherits from this
-    meta-object; otherwise returns 0.
+    meta-object; otherwise returns \nullptr.
 */
 const QObject *QMetaObject::cast(const QObject *obj) const
 {

src/corelib/kernel/qobject.cpp

@@ -2342,7 +2342,7 @@ static void err_info_about_objects(const char * func,
 
 /*!
     Returns a pointer to the object that sent the signal, if called in
-    a slot activated by a signal; otherwise it returns 0. The pointer
+    a slot activated by a signal; otherwise it returns \nullptr. The pointer
     is valid only during the execution of the slot that calls this
     function from this object's thread context.
 

src/corelib/plugin/qlibrary.cpp

@@ -999,7 +999,7 @@ void QLibrary::setFileNameAndVersion(const QString &fileName, const QString &ver
 
 /*!
     Returns the address of the exported symbol \a symbol. The library is
-    loaded if necessary. The function returns 0 if the symbol could
+    loaded if necessary. The function returns \nullptr if the symbol could
     not be resolved or if the library could not be loaded.
 
     Example:
@@ -1032,7 +1032,7 @@ QFunctionPointer QLibrary::resolve(const char *symbol)
     include the platform-specific file suffix; (see \l{fileName}). The
     library remains loaded until the application exits.
 
-    The function returns 0 if the symbol could not be resolved or if
+    The function returns \nullptr if the symbol could not be resolved or if
     the library could not be loaded.
 
     \sa resolve()
@@ -1052,7 +1052,7 @@ QFunctionPointer QLibrary::resolve(const QString &fileName, const char *symbol)
     (see \l{fileName}). The library remains loaded until the application exits.
     \a verNum is ignored on Windows.
 
-    The function returns 0 if the symbol could not be resolved or if
+    The function returns \nullptr if the symbol could not be resolved or if
     the library could not be loaded.
 
     \sa resolve()
@@ -1073,7 +1073,7 @@ QFunctionPointer QLibrary::resolve(const QString &fileName, int verNum, const ch
     (see \l{fileName}). The library remains loaded until the application exits.
     \a version is ignored on Windows.
 
-    The function returns 0 if the symbol could not be resolved or if
+    The function returns \nullptr if the symbol could not be resolved or if
     the library could not be loaded.
 
     \sa resolve()

src/corelib/plugin/qpluginloader.cpp

@@ -174,7 +174,7 @@ QPluginLoader::~QPluginLoader()
 
 /*!
     Returns the root component object of the plugin. The plugin is
-    loaded if necessary. The function returns 0 if the plugin could
+    loaded if necessary. The function returns \nullptr if the plugin could
     not be loaded or if the root component object could not be
     instantiated.
 

src/corelib/thread/qthread.cpp

@@ -920,7 +920,7 @@ QThreadPrivate::~QThreadPrivate()
     \since 5.0
 
     Returns a pointer to the event dispatcher object for the thread. If no event
-    dispatcher exists for the thread, this function returns 0.
+    dispatcher exists for the thread, this function returns \nullptr.
 */
 QAbstractEventDispatcher *QThread::eventDispatcher() const
 {

src/corelib/tools/qsharedpointer.cpp

@@ -875,7 +875,7 @@
     \b without ensuring that it cannot get deleted. To have that guarantee,
     use toStrongRef(), which returns a QSharedPointer object. If this
     function can determine that the pointer has already been deleted, it
-    returns 0.
+    returns \nullptr.
 
     It is ok to obtain the value of the pointer and using that value itself,
     like for example in debugging statements:

src/widgets/doc/src/widgets-and-layouts/styles.qdoc

@@ -286,7 +286,7 @@
     QStyleOption to a subclass (e.g., QStyleOptionFocusRect). For
     safety, you can use qstyleoption_cast() to ensure that the
     pointer type is correct. If the object isn't of the right type,
-    qstyleoption_cast() returns 0. For example:
+    qstyleoption_cast() returns \nullptr. For example:
 
     \snippet code/doc_src_qt4-styles.cpp 0
 

src/widgets/itemviews/qtablewidget.cpp

@@ -1813,7 +1813,7 @@ void QTableWidgetPrivate::_q_dataChanged(const QModelIndex &topLeft,
     \fn QTableWidgetItem *QTableWidget::itemAt(int ax, int ay) const
 
     Returns the item at the position equivalent to QPoint(\a{ax}, \a{ay}) in
-    the table widget's coordinate system, or returns 0 if the specified point
+    the table widget's coordinate system, or returns \nullptr if the specified point
     is not covered by an item in the table widget.
 
     \sa item()