Question

class A
{
public:
    A(…) {…}
    virtual ~A() {…}
    
private:
    // may contains data
};

class B : public A
{
public:
    B(…) {…}
private:
    // contains no data
};

class C : public B
{
public:
    C(…) {…}
    ~C() {…}
private:
    // may contains data
};

As you can see, class A is the base class so we have to provide a implemented virtual destructor.

Question> Do we have to provide a default destructor for a concrete class B?
class B itself doesn’t require to implement a customized destructor to release any allocated resource.

Thank you

Answer 1

No. Once one base destructor is virtual, all derived destructors are automatically virtual. If the default implementation suffices, you do not need to provide a user-defined destructor.

(In fact, if the default implementation suffices even in the base, you should declare and define it as virtual ~A() = default;, rather than with an empty body.)