Question

If we dont have virtual constructors then why we have virtual destructors? Can constructors also be virtual?

Answer 1

• There is no point in virtual constructor – you declare exactly what
  type is created, and it is well known in compile time. The compiler
  do not need [and actually cannot, since the dynamic dispatch is based
  on information which is created only after the object was created].
  So there are no virtual constructors.
• Virtual destructors are important to prevent memory leaks, and
  monitor the system. Assume you have A* a = new B; [B inherits
  from A], and you later delete a; – the compiler has no way of
  knowing a is a B [in the general case], and will invoke A‘s
  destructor – if it wasn’t virtual, and you might get a memory leak,
  or other faults.
• Using virtual destructor – you ensure that B‘s destructor is
  invoked, since a B object is being destroyed.