Inheriting from non-virtual dtor base class
-
I lately realized that classes like "QWidget ":http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/kernel/qwidget.h do not have a virtual dtor.
But still lot many classes are using QWidget for public inheritance.
And if I go by the guideline of "Herb Sutter - Guideline #4 in this article":http://www.gotw.ca/publications/mill18.htm then:
bq. A base class destructor should be either public and virtual, or protected and nonvirtual.
So what philosophy do we have in Qt regarding public base class's dtor ?
And what about the semi-destruction of object when deleted from base class pointer ?Thanks for your time.
shashank -
You forgot class QObject.
Just one virtual destructor at the top of the class hierarchy.Little example:
@
#include <iostream>using namespace std;
class VirtualBase
{
public:
VirtualBase()
{
cout << "VirtualBase: ktor (+1)" << endl;
}
virtual ~VirtualBase()
{
cout << "VirtualBase: dtor (-1)" << endl;
}
};class Base: public VirtualBase
{
public:
Base()
{
cout << "Base: ktor (+1)" << endl;
}
~Base()
{
cout << "Base: dtor (-1)" << endl;
}
};class Derive: public Base
{
public:
Derive()
{
cout << "Derive: ktor (+1)" << endl;
}
~Derive()
{
cout << "Derive: dtor (-1)" << endl;
}
};int main()
{
Base *base = new Derive();
delete base;return 0;}
@Output:
@
VirtualBase: ktor (+1)
Base: ktor (+1)
Derive: ktor (+1)
Derive: dtor (-1)
Base: dtor (-1)
VirtualBase: dtor (-1)
@Analogues:
@
virtual ~QObject(); // As VirtualBase
~QWidget(); // As Base
@
