virtual destructor

code 1. 

#include <iostream>
using namespace std;

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

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

int main()
{
Derived *p = new Derived;
delete p;

return 0;
}

---------------------

[tli]$ ./a.out
Base constructor
Derived constructor
Derived destructor
Base destructor

code 2.

#include <iostream>
using namespace std;

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

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

int main()
{
Base *p = new Derived;
delete p;

return 0;
}

-----

[tli]$ ./a.out
Base constructor
Derived constructor
Base destructor

code 3.

#include <iostream>
using namespace std;

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

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

int main()
{
Base *p = new Derived;
delete p;

return 0;
}

[tli]$ ./a.out
Base constructor
Derived constructor
Derived destructor
Base destructor