Why Parent class in constructor?

pk23081996

I was strolling through the Qt examples and saw this:

class MainWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MainWidget(QWidget *parent = 0);
    ....
}

I was curious to know why do we need to pass a parent object to the constructor? Is this only to maintain a parent-child relationship or does it serve some another purpose as well?

And what does this statement do? : 
MainWidget::MainWidget(QWidget *parent) :
                    **QWidget(parent)**
{ }

We initialize a QWidget object with the parent here but what does it actually do?
Thanks

jsulm

@pk23081996 said in Why Parent class in constructor?:

Is this only to maintain a parent-child relationship

Yes, parent/child.
What parent means for QWidget based classes (in addition to parent/child based memory management) can be found here: https://doc.qt.io/qt-5/qwidget.html#QWidget

Pablo J. Rogina

@pk23081996 said in Why Parent class in constructor?:

We initialize a QWidget object with the parent here but what does it actually do?

Look at the documentation about object trees & ownership. One main benefit is:

When you create a QObject with another object as parent, it's added to the parent's children() list, and is deleted when the parent is