Calling virtual functions inside constructors

Question

Suppose I have two C++ classes:

class A
{
public:
  A() { fn(); }

  virtual void fn() { _n = 1; }
  int getn() { return _n; }

protected:
  int _n;
};

clas         


        

Answer 1

During the object's constructor call the virtual function pointer table is not completely built. Doing this will usually not give you the behavior you expect. Calling a virtual function in this situation may work but is not guaranteed and should be avoided to be portable and follow the C++ standard.