Destruction of class members when destructor is not called

Question

In the following code, when ptr is deleted, the destructor for Base is called, but not the destructor for Derived (due to destructor of Base not being virtual).

class Base
{
  int b;
};

class Derived : public Base
{
  int d;
};

int main(void)
{
    Base * ptr = new Derived();
    delete ptr;
    return 0;
}

Valgrind reports that the program contains no memory leaks, which i guess is true in the sense that all newed data is deleted in this particular case. My question is - given that the (default) destructor of Derived is not called, when and how is the memory for d deallocated or reclaimed?

Answer 1

It is Undefined behavior to call delete on a base class pointer pointing to a derived class object if the destructor in base class is not virtual.

Undefined behavior means that anything can happen. Whether memory leaks or not is irrelevant the fact is that your program can show any behavior and you cannot rely on any behavior that is shown.

For your code to be valid the destructor in Base class must be virtual.

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C++11 Standard 5.3.5 Delete:
Para 3:

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. In the second alternative (delete array) if the dynamic type of the object to be deleted differs from its static type, the behavior is undefined.