default override of virtual destructor

Everyone knows that the desructor of base class usually has to be virtual. But what is about the destructor of derived class? In C++11 we have keyword "override" and ability to use the default destructor explicitly.

struct Parent
{
  std::string a;
  virtual ~Parent()
  {
  }

};

struct Child: public Parent
{
  std::string b;
  ~Child() override = default;
};

Is it correct to use both keywords "override" and "=default" in the destructor of Child class? Will compiler generate correct virtual destructor in this case?

If yes, then can we think that it is good coding style, and we should always declare destructors of derived classes this way to ensure that base class destructors are virtual?

Solution 1:

Is it correct to use both keywords "override" and "=default" in the destructor of Child class? Will compiler generate correct virtual destructor in this case?

Yes, it is correct. On any sane compiler, if the code compiles without error, this destructor definition will be a no-op: its absence must not change the behavior of the code.

can we think that it is good coding style

It's a matter of preference. To me, it only makes sense if the base class type is templated: it will enforce a requirement on the base class to have a virtual destructor, then. Otherwise, when the base type is fixed, I'd consider such code to be noise. It's not as if the base class will magically change. But if you have deadheaded teammates that like to change things without checking the code that depends on what they may be possibly breaking, it's best to leave the destructor definition in - as an extra layer of protection.

Solution 2:

override is nothing more than a safety net. Destructor of the child class will always be virtual if base class destructor is virtual, no matter how it is declared - or not declared at all (i.e. using implicitly declared one).