Virtual Destructor

We already studies what is Destructor and virtual function. The combination of Virtual keyword what we studied in Virtual function and Destructor is nothing but Virtual Destructor. A virtual destructor is used to free up the memory space allocated by the derived class object or instance while deleting instances of the derived class using a base class pointer object. A base or parent class destructor use the virtual keyword that ensures both base class and the derived class destructor will be called at run time, but it called the derived class first and then base class to release the space occupied by both destructors.

Syntax
virtual ~className(){

}

CODE

EG 1 . Creating a parent class with virtual destructor.

#include <iostream>
using namespace std;

class BaseClass {
  public:
    BaseClass() {
        cout << "Base class constructor invoked" << endl;
    }
    virtual ~BaseClass() {
        cout << "Base class virtual destructor invoked" << endl;
    }
};

class DerivedClass : public BaseClass {
  public:
    DerivedClass() {
        cout << "Derived class constructor invoked" << endl;
    }
    ~DerivedClass() {
        cout << "Derived class destructor invoked" << endl;
    }
};

int main() {
    //UPCASTING
    BaseClass* obj1 = new DerivedClass();
    //We can delete object inside code itself
    delete obj1;
}

OUTPUT
Base class constructor invoked
Derived class constructor invoked
Derived class destructor invoked
Base class virtual destructor invoked

CODE EXPLANATION
In the above code, we created 2 classes called BaseClass and DerivedClass where BaseClass is the parent class of DerivedClass. BaseClass is having a constructor and a virtual destructor. DerivedClass which is the child class of BaseClass is also having a constructor and a destructor. Inside main method we used upcasting to assign child class object to its parent class reference(obj1). If we run above program first Base class constructor will be invoked, then derived class constructor will be invoked since we assigned child class object to its parent class reference(obj1). After this we are deleting obj1, so that obj1 will be no longer in use hence destructors will be invoked. we have used a virtual destructor inside the BaseClass that calls the DerivedClass destructor before calling the base class destructor and release the spaces or resolve the memory leak issue in the program.


What is the use of virtual destructor?
When destroying instances of a derived class using a base class pointer object, a virtual destructor is used to free up memory space allocated by the derived class object or instance. It will resolve the memory leak issue in the program.