When to use virtual destructors in c++?

Answer:

When we will delete an object of the derived class using a pointer to the base class that has a non-virtual destructor a results in undefined behavior.

So virtual destructors are useful when you might potentially delete an instance of a derived class through a pointer to the base class. Let see an example code,

#include<iostream>
using namespace std;
class base
{
public:
    base()
    {
        cout<<"Constructing base \n";
    }
    virtual ~base()
    {
        cout<<"Destructing base \n";
    }
};
class derived: public base
{
public:
    derived()
    {
        cout<<"Constructing derived \n";
    }
    ~derived()
    {
        cout<<"Destructing derived \n";
    }
};
int main()
{
    derived *d = new derived();
    base *b = d;
    delete b;
    return 0;
}

Output: