Virtual Destructors¶

Is-A Relationships And Destructors ¶

From Destructors And Inheritance: simple/naive destructors are not enough when using object polymorpically
Much like simple/naive methods vs. virtual methods
⟶ virtual destructors, starting at the root of inheritance
⟶ dynamic dispatch to destructor of concrete object’s class
⟶ correct cleanup

code/inher-oo-dtor-derived-virtual.cpp¶

#include <iostream>


class Base
{
public:
    virtual ~Base()             // <--- Preparing polymorpic usage of derived classes
    {
        std::cout << "Base::~Base()" << std::endl;
    }
};

class Derived : public Base
{
public:
    virtual ~Derived()          // <--- "virtual" not strictly necessary, but good style
    {
        std::cout << "Derived::~Derived()" << std::endl;
    }
};

int main()
{
    Base* b = new Derived;      // <--- Base* points to Derived object
    delete b;                   // <--- Polymorphic usage: entering cleanup at Derived::~Derived()

    return 0;
}

$ ./inher-oo-dtor-derived-virtual
Derived::~Derived()
Base::~Base()

Pure Virtual Destructor?¶

Object destruction calls every destructor up to the innermost base class
⟶ Destructors cannot be pure virtual

code/inher-oo-dtor-pure-virtual.cpp¶

#include <iostream>


class Base
{
public:
    virtual ~Base() = 0;
};

class Derived : public Base
{
public:
    virtual ~Derived() 
    {
    }
};

int main()
{
    Derived d;

    return 0;
}

inher-oo-dtor-pure-virtual.cpp:15: undefined reference to `Base::~Base()'
collect2: error: ld returned 1 exit status