Virtual destructors?

For Beginners

Started by Tomoso January 04, 2003 05:33 PM

1 comment, last by Tomoso 21 years, 10 months ago

Tomoso

Author

122

January 04, 2003 05:33 PM

Whats teh difference between a Virtual Destructor and a normal one?

Tomoso

Alimonster

185

January 04, 2003 05:46 PM

    #include <iostream>class CBase{public:    virtual ~CBase() { std::cout << "base class" << std::endl; }};class CSub: public CBase{public:    ~CSub() { std::cout << "Dying now" << std::endl; }};int main(){    CBase* x = new CSub;    delete x;    return 0;}

versus

        #include <iostream>class CBase{public:   ~CBase() { std::cout << "base class" << std::endl; }};class CSub: public CBase{public:    ~CSub() { std::cout << "Never shown" << std::endl; }};int main(){    CBase* x = new CSub;    delete x;    return 0;};

The first one will correctly kill the sub-class because the destructor is virtual, so it can be polymorphic. The second one won't resulting in possible memory leaks (only the CBase destructor will be called - there's no polymorphism, so it sees x as a CBase rather than a CSub class, since that's what it's a pointer to initially).

If you expect the base class to be derived from then use a virtual destructor. The virtual destructor will behave polymorphically when required, which is rather handy.

[edited by - Alimonster on January 4, 2003 6:47:47 PM]