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c++virtualdelete-operatorvirtual-destructor

What happens when delete a polymorphic object without a virtual destructor?

In following example, b is a polymorphic pointer type whose static type is Base* and whose dynamic type is Derived*.

struct Base 
{
  virtual void f();
};

struct Derived : Base 
{ 

};

int main()
{
   Base *b = new Derived();
   // ...
   delete b;
}

What happens when b is deleted without a virtual destructor?

Solution

  • What happens when b is deleted without a virtual destructor?

    We don't know. The behavior is undefined. For most actual cases the destructor of Derived might no be invoked, but nothing is guaranteed.

    5.3.5 Delete [expr.delete]

    (emphasis mine)

    In the first alternative (delete object), if the static type of the object to be deleted is different from its dynamic type, the static type shall be a base class of the dynamic type of the object to be deleted and the static type shall have a virtual destructor or the behavior is undefined.