Give some simple recommendation for when a destructor should be declared virtual.

Question

What will be an ideal response?

Answer 1

The short answer: The base class destructor should always be virtual. It costs very
little. Just do it.
A somewhat longer answer is: You need a virtual base class destructor when your
program applies the delete operator to a base class pointer that actually points to a
derived class object. Conversely, if the base class does not have a virtual destructor,
classes that inherit from the base class should not have a destructor at all.
A detailed answer is:
IF
a) Some constructor at any level of inheritance beyond the base class separately
allocates resources (we have seen only memory, but there are other resources to
be allocated) and
b) The program dynamically allocates an object of a class at any level beyond the
base class
THEN
The base class destructor should be virtual. The consequences a non-virtual
destructor are an almost certain memory leak of all memory allocated at any level
beyond the base class.