Why C++ does not have a virtual constructor?

The virtual mechanism works only when we have a base class pointer to a derived class object.

In C++, constructor cannot be virtual, because when constructor of a class is executed there is no virtual table in the memory, means no virtual pointer defined yet. So, the constructor should always be non-virtual.

But virtual destructor is possible. Here is an example

Example

#include<iostream>
using namespace std;
class b {
   public:
   b()
   { cout<<"Constructing base \n"; }
   virtual ~b()
   { cout<<"Destructing base \n"; }
};
class d: public b {
   public:
      d()
      { cout<<"Constructing derived \n"; }
      ~d()
      { cout<<"Destructing derived \n"; }
};
int main(void) {
   d *derived = new d();
   b *bptr = derived;
   delete bptr;
   return 0;
}

Output

Constructing base
Constructing derived
Destructing derived
Destructing base