QtGui: 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: Ieffbfffa76e3018257b667a3e8ad6e3b88486cde
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/gui/image/qimageiohandler.cpp

@@ -340,7 +340,7 @@ void QImageIOHandler::setDevice(QIODevice *device)
 
 /*!
     Returns the device currently assigned to the QImageIOHandler. If
-    not device has been assigned, 0 is returned.
+    not device has been assigned, \nullptr is returned.
 */
 QIODevice *QImageIOHandler::device() const
 {

src/gui/image/qimagereader.cpp

@@ -756,13 +756,13 @@ void QImageReader::setDevice(QIODevice *device)
     d->device = device;
     d->deleteDevice = false;
     delete d->handler;
-    d->handler = 0;
+    d->handler = nullptr;
     d->text.clear();
 }
 
 /*!
-    Returns the device currently assigned to QImageReader, or 0 if no
+    Returns the device currently assigned to QImageReader, or \nullptr
-    device has been assigned.
+    if no device has been assigned.
 */
 QIODevice *QImageReader::device() const
 {

src/gui/image/qimagewriter.cpp

@@ -407,8 +407,8 @@ void QImageWriter::setDevice(QIODevice *device)
 }
 
 /*!
-    Returns the device currently assigned to QImageWriter, or 0 if no
+    Returns the device currently assigned to QImageWriter, or \nullptr
-    device has been assigned.
+    if no device has been assigned.
 */
 QIODevice *QImageWriter::device() const
 {

src/gui/image/qmovie.cpp

@@ -659,7 +659,7 @@ void QMovie::setDevice(QIODevice *device)
 
 /*!
     Returns the device QMovie reads image data from. If no device has
-    currently been assigned, 0 is returned.
+    currently been assigned, \nullptr is returned.
 
     \sa setDevice(), fileName()
 */

src/gui/image/qpicture.cpp

@@ -1200,8 +1200,8 @@ QT_END_INCLUDE_NAMESPACE
     \obsolete
 
     Returns a string that specifies the picture format of the file \a
-    fileName, or 0 if the file cannot be read or if the format is not
+    fileName, or \nullptr if the file cannot be read or if the format
-    recognized.
+    is not recognized.
 
     \sa load(), save()
 */
@@ -1543,7 +1543,7 @@ const QPicture &QPictureIO::picture() const { return d->pi; }
 int QPictureIO::status() const { return d->iostat; }
 
 /*!
-    Returns the picture format string or 0 if no format has been
+    Returns the picture format string or \nullptr if no format has been
     explicitly set.
 */
 const char *QPictureIO::format() const { return d->frmt; }

src/gui/kernel/qcursor.cpp

@@ -564,8 +564,8 @@ void QCursor::setShape(Qt::CursorShape shape)
 }
 
 /*!
-    Returns the cursor bitmap, or 0 if it is one of the standard
+    Returns the cursor bitmap, or \nullptr if it is one of the
-    cursors.
+    standard cursors.
 */
 const QBitmap *QCursor::bitmap() const
 {
@@ -575,8 +575,8 @@ const QBitmap *QCursor::bitmap() const
 }
 
 /*!
-    Returns the cursor bitmap mask, or 0 if it is one of the standard
+    Returns the cursor bitmap mask, or \nullptr if it is one of the
-    cursors.
+    standard cursors.
 */
 
 const QBitmap *QCursor::mask() const

src/gui/kernel/qopenglcontext.cpp

@@ -414,15 +414,14 @@ int QOpenGLContextPrivate::maxTextureSize()
 
 /*!
     Returns the last context which called makeCurrent in the current thread,
-    or 0, if no context is current.
+    or \nullptr, if no context is current.
 */
 QOpenGLContext* QOpenGLContext::currentContext()
 {
     QGuiGLThreadContext *threadContext = qwindow_context_storage()->localData();
-    if (threadContext) {
+    if (threadContext)
         return threadContext->context;
-    }
+    return nullptr;
-    return 0;
 }
 
 /*!

src/gui/kernel/qplatformwindow.cpp

@@ -90,11 +90,11 @@ QWindow *QPlatformWindow::window() const
 }
 
 /*!
-    Returns the parent platform window (or 0 if orphan).
+    Returns the parent platform window (or \nullptr if orphan).
 */
 QPlatformWindow *QPlatformWindow::parent() const
 {
-    return window()->parent() ? window()->parent()->handle() : 0;
+    return window()->parent() ? window()->parent()->handle() : nullptr;
 }
 
 /*!

src/gui/painting/qpainter.cpp

@@ -1521,7 +1521,7 @@ QPainter::~QPainter()
 
 /*!
     Returns the paint device on which this painter is currently
-    painting, or 0 if the painter is not active.
+    painting, or \nullptr if the painter is not active.
 
     \sa isActive()
 */

src/gui/text/qtextdocumentwriter.cpp

@@ -206,8 +206,8 @@ void QTextDocumentWriter::setDevice (QIODevice *device)
 }
 
 /*!
-    Returns the device currently assigned, or 0 if no device has been
+    Returns the device currently assigned, or \nullptr if no device
-    assigned.
+    has been assigned.
 */
 QIODevice *QTextDocumentWriter::device () const
 {

src/gui/text/qtextobject.cpp

@@ -704,8 +704,8 @@ QTextFrame::iterator &QTextFrame::iterator::operator=(const iterator &other) Q_D
 #endif
 
 /*!
-    Returns the current frame pointed to by the iterator, or 0 if the
+    Returns the current frame pointed to by the iterator, or \nullptr
-    iterator currently points to a block.
+    if the iterator currently points to a block.
 
     \sa currentBlock()
 */
@@ -1291,12 +1291,12 @@ QVector<QTextLayout::FormatRange> QTextBlock::textFormats() const
 }
 
 /*!
-    Returns the text document this text block belongs to, or 0 if the
+    Returns the text document this text block belongs to, or \nullptr
-    text block does not belong to any document.
+    if the text block does not belong to any document.
 */
 const QTextDocument *QTextBlock::document() const
 {
-    return p ? p->document() : 0;
+    return p ? p->document() : nullptr;
 }
 
 /*!
@@ -1306,7 +1306,7 @@ const QTextDocument *QTextBlock::document() const
 QTextList *QTextBlock::textList() const
 {
     if (!isValid())
-        return 0;
+        return nullptr;
 
     const QTextBlockFormat fmt = blockFormat();
     QTextObject *obj = p->document()->objectForFormat(fmt);