in C++ a destructor is generally used to deallocate memory and do some other cleanup for a class object and it’s class members whenever an object is destroyed. Destructors are distinguished by the tilde, the ‘~’that appears in front of the destructor name. In order to define a virtual destructor, all you have to do is simply add the keyword “virtual” before the tilde symbol.
If the destructor in the base class is not made virtual, then an object that might have been declared of type base class and instance of child class would simply call the base class destructor without calling the derived class destructor.
Hence, by making the destructor in the base class virtual, we ensure that the derived class destructor gets called before the base class destructor.
class a
{
public:
a(){printf("\nBase Constructor\n");}
~a(){printf("\nBase Destructor\n");}
};
class b : public a
{
public:
b(){printf("\nDerived Constructor\n");}
~b(){printf("\nDerived Destructor\n");}
};
int main()
{
a* obj=new b;
delete obj;
return 0;
}
Output:
Base Constructor
Derived Constructor
Base Destructor
By Changing
~a(){printf("\nBase Destructor\n");}
to
virtual ~a(){printf("\nBase Destructor\n");}
Output:
Base Constructor
Derived Constructor
Derived Destructor
Base Destructor
