QtBase: replace 0 with \nullptr in documentation

Replace 0 with \nullptr in the documentation.
As a drive-by also replace some 0 with nullptr in the corresponding
code.

Change-Id: I914b6b2151554c06acc2d244eff004524cbb9a82
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/network/access/qabstractnetworkcache.cpp

@@ -475,7 +475,7 @@ QAbstractNetworkCache::~QAbstractNetworkCache()
     the QIODevice when done with it.
 
     If there is no cache for \a url, the url is invalid, or if there
-    is an internal cache error 0 is returned.
+    is an internal cache error \nullptr is returned.
 
     In the base class this is a pure virtual function.
 
@@ -496,7 +496,7 @@ QAbstractNetworkCache::~QAbstractNetworkCache()
     Returns the device that should be populated with the data for
     the cache item \a metaData.  When all of the data has been written
     insert() should be called.  If metaData is invalid or the url in
-    the metadata is invalid 0 is returned.
+    the metadata is invalid \nullptr is returned.
 
     The cache owns the device and will take care of deleting it when
     it is inserted or removed.

src/opengl/qgl.cpp

@@ -4119,14 +4119,14 @@ void QGLWidget::swapBuffers()
 /*!
     \fn const QGLContext* QGLWidget::overlayContext() const
 
-    Returns the overlay context of this widget, or 0 if this widget
-    has no overlay.
+    Returns the overlay context of this widget, or \nullptr if this
+    widget has no overlay.
 
     \sa context()
 */
 const QGLContext* QGLWidget::overlayContext() const
 {
-    return 0;
+    return nullptr;
 }
 
 /*!

src/sql/models/qsqlrelationaltablemodel.cpp

@@ -626,8 +626,8 @@ QString QSqlRelationalTableModel::selectStatement() const
 
 /*!
     Returns a QSqlTableModel object for accessing the table for which
-    \a column is a foreign key, or 0 if there is no relation for the
-    given \a column.
+    \a column is a foreign key, or \nullptr if there is no relation for
+    the given \a column.
 
     The returned object is owned by the QSqlRelationalTableModel.
 
@@ -636,12 +636,12 @@ QString QSqlRelationalTableModel::selectStatement() const
 QSqlTableModel *QSqlRelationalTableModel::relationModel(int column) const
 {
     Q_D(const QSqlRelationalTableModel);
-    if ( column < 0 || column >= d->relations.count())
-        return 0;
+    if (column < 0 || column >= d->relations.count())
+        return nullptr;
 
     QRelation &relation = const_cast<QSqlRelationalTableModelPrivate *>(d)->relations[column];
     if (!relation.isValid())
-        return 0;
+        return nullptr;
 
     if (!relation.model)
         relation.populateModel();

src/xml/sax/qxml.cpp

@@ -2676,9 +2676,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlEntityResolver* QXmlReader::entityResolver() const
+    \fn QXmlEntityResolver *QXmlReader::entityResolver() const
 
-    Returns the entity resolver or 0 if none was set.
+    Returns the entity resolver or \nullptr if none was set.
 
     \sa setEntityResolver()
 */
@@ -2692,9 +2692,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlDTDHandler* QXmlReader::DTDHandler() const
+    \fn QXmlDTDHandler *QXmlReader::DTDHandler() const
 
-    Returns the DTD handler or 0 if none was set.
+    Returns the DTD handler or \nullptr if none was set.
 
     \sa setDTDHandler()
 */
@@ -2708,9 +2708,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlContentHandler* QXmlReader::contentHandler() const
+    \fn QXmlContentHandler *QXmlReader::contentHandler() const
 
-    Returns the content handler or 0 if none was set.
+    Returns the content handler or \nullptr if none was set.
 
     \sa setContentHandler()
 */
@@ -2725,9 +2725,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlErrorHandler* QXmlReader::errorHandler() const
+    \fn QXmlErrorHandler *QXmlReader::errorHandler() const
 
-    Returns the error handler or 0 if none is set.
+    Returns the error handler or \nullptr if none is set.
 
     \sa setErrorHandler()
 */
@@ -2741,9 +2741,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlLexicalHandler* QXmlReader::lexicalHandler() const
+    \fn QXmlLexicalHandler *QXmlReader::lexicalHandler() const
 
-    Returns the lexical handler or 0 if none was set.
+    Returns the lexical handler or \nullptr if none was set.
 
     \sa setLexicalHandler()
 */
@@ -2757,9 +2757,9 @@ void QXmlSimpleReaderPrivate::initIncrementalParsing()
 */
 
 /*!
-    \fn QXmlDeclHandler* QXmlReader::declHandler() const
+    \fn QXmlDeclHandler *QXmlReader::declHandler() const
 
-    Returns the declaration handler or 0 if none was set.
+    Returns the declaration handler or \nullptr if none was set.
 
     \sa setDeclHandler()
 */