If I understand the QWidget documentation correctly, there is no need to delete children widgets when deleting the parent widget.

QWidget::QWidget ( QWidget * parent = 0, Qt::WindowFlags f = 0 )

Constructs a widget which is a child of parent, with widget flags set to f.

If parent is 0, the new widget becomes a window. If parent is another widget, this widget becomes a child window inside parent. The new widget is deleted when its parent is deleted.
QWidget::~QWidget ()

Destroys the widget.

All this widget's children are deleted first. The application exits if this widget is the main widget.
However, I wrote the following test program, where I intentionally delete the children widgets in the parent's destructor and it deleted everything just fine. So it seems that I do need to explicitly delete the children widgets before deleting the parent widget, else it might lead to memory leak. But then I don't understand what the quoted QWidget documentation above. Can someone please explain to me what's the correct way? Thanks a bunch!

Qt Code: 
  1. #include <QApplication>
  2. #include <QtAlgorithms>
  3. #include <QMainWindow>
  4. #include <QtGui/QLabel>
  5. #include <QtGui/QTabWidget>
  6.  
  7. class B : public QWidget
  8. {
  9.     public:
  10.         B() : mLabel(new QLabel(this))
  11.         {
  12.             printf("B constructor\n");
  13.         }
  14.  
  15.         ~B() 
  16.         {
  17.             printf("B destructor delete label\n");
  18.             delete mLabel;
  19.         }
  20.  
  21.     private:
  22.         QLabel* mLabel;
  23. };
  24.  
  25.  
  26. class A : public QMainWindow
  27. {
  28.     public:
  29.         A() :
  30.             mLabel(new QLabel(this)),
  31.             mTab(new QTabWidget(this)),
  32.             mB(new B())
  33.         {
  34.             printf("A constructor\n");
  35.             mTab->addTab(mB, "B");
  36.         }
  37.  
  38.         ~A()
  39.         {
  40.             printf("A destructor delete label\n");
  41.             delete mLabel;
  42.             printf("A destructor delete B\n");
  43.             delete mB;
  44.             printf("A destructor delete tab\n");
  45.             delete mTab;
  46.         }
  47.  
  48.     private:
  49.         QLabel* mLabel;
  50.         QTabWidget* mTab;
  51.         B* mB;
  52.  
  53. };
  54.  
  55. int main(int argc, char *argv[])
  56. {
  57.     QApplication app(argc, argv);
  58.  
  59.     A* a = new A();
  60.     delete a;
  61.  
  62.    return app.exec();
  63. }
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