virtual Constructors/Destructors

Can we have a virtual constructor ? a virtual destructor?
if yes ,why? and if not,why?

suppose A is the base class,b the derived class.
A *bptr = new B;

Virtual destructor:
becomes helpful to clear up the space allocated to bptr.
NOTE: without virtual destructor it would not be possible to clear up properly the elements that only belong to B.

Virtual constructor
is redundant because any way the 'new B' will call both B's constructor and A's constructor.

there can't be any virtual constructor.because when obect is being created then object doesn't know the classes derivered from it so it can;t call any derived function