Question

I have two classes A and B such that A has a static B instance as its member. B has a function Show() and here is my class A:

class A
{
  A()
  {
    _b.Show();
  }
private:

  static B _b; 
};

and subsequent code is

A a;
B A::_b;

int main()
{
}

Now B::Show() called before B is constructed due to the sequence in which I have defined
a and _b. But how does this work exactly i.e. how is it possible to make calls on an object that is still not constructed ?

Answer 1

It’s not possible, it’s undefined behavior (in this case, because you’re accessing an uninitialized object) because a is initialized before A::_b.

Look up static initialization order fiasco. You don’t get an error because 99% of the times this happens, it’s not easily diagnosable.