Automatic deletion of class member variables in QT

Qt Enthusiast

Hi All
I have class

class myShortCut
class myShortCut: QShortCut 
{
   myShortCut(QWidget* parent = 0 ) ;
   ~myShortCut()  { qDebug() << "\n I am in Destruct or of myShortcut" ; }
 private:
  int *i;
};

// constructor of myShortCut
myShortCut::myShortCut(QWidget* parent):QShortcut(QKeySequence(Qt::CTRL + Qt::Key_R),parent) 
{
      i  = new int;
     *i = 1;
      qDebug() <<  " In constructor of myShortCut";
 }

// class myView
class myView : public QTextEdit
{
  Q_OBJECT
public:
    myView(QWidget* parent);
   ~myView();
    myShortcut*    shortCut
};

myView ::myView () {
     shortCut = new QShortCut(this)
}

myView ::~myView () {
}

When I close the gui the Even if I do not delete the shortCut member variable in destruct or of myView , the destructor of myShorcut is called

Also I tried to put a delete shortCut in destructor of myView

myView ::~myView () {
 delete shortCut
}

then also he destructor of myShorcut is called

Can someone comment of how automatic deletion class variables works in QT when the gui is close

[Fixed code formatting. ~kshegunov]

kshegunov

@Qt-Enthusiast said:

Can someone comment of how automatic deletion class variables works in QT when the gui is close

This has no relation to the GUI. QObject instances will delete their children in the destructor ensuring that child objects are not left dangling in memory (i.e not leaking memory). By giving a parent to a QObject subclass (QShortcut here):

 shortCut = new QShortcut(this)

you're also adding the newly created object as a child to this (being of type myView in this case). Ultimately when the destructors are called the shortcut will be deleted.

Qt Enthusiast

Two more questions

What if I have following code.. Will shortCut variable will be deleted automatically

myView ::myView () {
shortCut = new QShortCut
}
Also What if shortCut is a local variable instead of class variable then ?
Could you point me the documentation when such concept is mentioned , regarding Q_Object automatically deletes its children

kshegunov

@Qt-Enthusiast

What if I have following code.. Will shortCut variable will be deleted automatically

No, because there's no parent specified, so the QObject will not be owned by another QObject, thus no one will be bound to deleting it automatically.

Also What if shortCut is a local variable instead of class variable then ?

As any C++ stack allocated local variable, going out of scope (unwinding the stack) will free the memory after running the corresponding destructors. As for heap allocations - it's up to the programmer to manage the heap, so no automatic deletion shall be happening when a local pointer goes out of scope.

Could you point me the documentation when such concept is mentioned , regarding Q_Object automatically deletes its children

http://doc.qt.io/qt-5/objecttrees.html