Doc snippets: Use nullptr instead of 0 literal

Also mark constructors explicit, where applicable.

Pick-to: 5.15
Fixes: QTBUG-84859
Change-Id: I145d366d854fd6b4373bcc23d0b880d6361d9014
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/gui/doc/snippets/clipboard/clipwindow.h

@@ -65,7 +65,7 @@ class ClipWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    ClipWindow(QWidget *parent = 0);
+    explicit ClipWindow(QWidget *parent = nullptr);
 
 public slots:
     void updateClipboard();

src/gui/doc/snippets/code/src_gui_opengl_qopenglfunctions.cpp

@@ -53,7 +53,7 @@
     {
         Q_OBJECT
     public:
-        MyGLWindow(QScreen *screen = 0);
+        explicit MyGLWindow(QScreen *screen = nullptr);
 
     protected:
         void initializeGL();

src/gui/doc/snippets/draganddrop/dragwidget.h

@@ -66,7 +66,7 @@ class DragWidget : public QFrame
     Q_OBJECT
 
 public:
-    DragWidget(QWidget *parent);
+    explicit DragWidget(QWidget *parent = nullptr);
     void setData(const QString &mimetype, const QByteArray &newData);
 
 signals:

src/gui/doc/snippets/draganddrop/mainwindow.h

@@ -67,7 +67,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    explicit MainWindow(QWidget *parent = nullptr);
 
 public slots:
     void setDragResult(const QString &actionText);

src/gui/doc/snippets/dragging/mainwindow.h

@@ -65,7 +65,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    explicit MainWindow(QWidget *parent = nullptr);
 
 protected:
     void mousePressEvent(QMouseEvent *event) override;

src/gui/doc/snippets/dropevents/window.h

@@ -64,7 +64,7 @@ class Window : public QWidget
     Q_OBJECT
 
 public:
-    Window(QWidget *parent = 0);
+    explicit Window(QWidget *parent = nullptr);
 
 protected:
     void dragEnterEvent(QDragEnterEvent *event) override;

src/gui/doc/snippets/droprectangle/window.h

@@ -64,7 +64,7 @@ class Window : public QWidget
     Q_OBJECT
 
 public:
-    Window(QWidget *parent = 0);
+    explicit Window(QWidget *parent = nullptr);
 
 protected:
     void dragMoveEvent(QDragMoveEvent *event) override;

src/gui/doc/snippets/plaintextlayout/window.h

@@ -58,7 +58,7 @@ class Window : public QWidget
     Q_OBJECT
 
 public:
-    Window(QWidget *parent = 0);
+    explicit Window(QWidget *parent = nullptr);
 
 protected:
     void paintEvent(QPaintEvent *event) override;

src/gui/doc/snippets/qstatustipevent/main.cpp

@@ -54,7 +54,7 @@
 class MainWindow : public QMainWindow
 {
 public:
-    MainWindow(QWidget *parent = 0);
+    explicit MainWindow(QWidget *parent = nullptr);
 };
 
 //! [0] //! [1]

src/gui/doc/snippets/scribe-overview/main.cpp

@@ -68,7 +68,7 @@ void mergeFormat(QTextEdit *edit)
 
 int main(int argc, char *argv[])
 {
-    QWidget *parent = 0;
+    QWidget *parent = nullptr;
     QString aStringContainingHTMLtext("<h1>Scribe Overview</h1>");
 
     QApplication app(argc, argv);

src/gui/doc/snippets/textdocument-imagedrop/textedit.h

@@ -58,7 +58,7 @@ class TextEdit : public QTextEdit
     Q_OBJECT
 
 public:
-    TextEdit(QWidget *parent=0);
+    explicit TextEdit(QWidget *parent = nullptr);
     bool canInsertFromMimeData( const QMimeData *source ) const override;
     void insertFromMimeData( const QMimeData *source ) override;
 };