// Forward declare the inner class
class inner;

// The actual outer class.
class outer {
 public:

   // This is the function you would like to call.
   int get_data();

 private:
   inner _inner;
}

// The actual definition of the inner class.
class inner {
  public:
    inner(outer& o) : _outer(o) // Set the reference.
    {

    }

    // The function using the data in outer.
    void do_stuff()
    {
      int x = _outer.get_data() + 5;
    }

  private:
    // A reference to the outer class.
    outer& _outer;

}

__this = (outer*)((unsigned long long)this - (unsigned long long)(&((outer*)0)->inner_instance));