c++ call class's function of another class's function

i hope this makes sense for you, i get confused. let me know if there is a simpler way:

double A::a(double(b::*bb)())开发者_C百科
{
  b.init();
  return (b->*bb)();
}

void A::run();
{
  cout<< a(b.b1);
  cout<< a(b.b2);
}

class A
{
  B b;
  void run();
  double a(double(b::*bb)());
};

class B
{
  void init();
  double b1();
  double b2();
};

It doesn't make sense. This makes sense though:

class B // <- class B definition comes first
{
  void init();
  double b1();
  double b2();
};

class A
{
  B b;
  void run();
  double a(double(B::*bb)()); // <- B instead of b
};

double A::a(double(B::*bb)()) // <- B instead of b
{
  b.init();
  return (b->*bb)();
}

void A::run() // <- you can't put semicolon here
{
  cout<< a(&B::b1); // <- you want to pass the address of a member.
  cout<< a(&B::b2); // <- you want to pass the address of a member.
}

Now it makes more sense to me.

This:

double a(double(b::*bb)());

Should be:

double a(double(B::*bb)());

That is, bb is to be declared as a pointer to member function in the class B, not in the object b (which is an instance, not a type itself, therefore cannot be part of a type).