Inheritance from a purely abstract class. Not included?

Question

OOP

#pragma once
#include "Vector.h"
class AbstractFigure
{
public:
  virtual void Scale() = 0;
  virtual void Rotate() = 0;
  virtual void Move(Vector direction) = 0;
};

#pragma once
#include "AbstractFigure.h"
class Point :
  public AbstractFigure
{
public:
  Point();
  ~Point();

  // Inherited via AbstractFigure
  virtual void Scale() override;
  virtual void Rotate() override;
  virtual void Move(Vector direction) override;
};

#pragma once
#include "AbstractFigure.h"
class Vector :
  public AbstractFigure
{
public:
  Vector();
  ~Vector();

  // Inherited via AbstractFigure
  virtual void Scale() override;
  virtual void Rotate() override;
  virtual void Move(Vector direction) override;
};

Errors C2504 'AbstractFigure': base class undefined

Answer 1

#pragma once
#include "Vector.h"
class AbstractFigure
...
#pragma once
#include "AbstractFigure.h"
class Vector :
public AbstractFigure
...
No, it won't. Because either AbstractFigure.h is the first one, or Vector.h, someone will be out of luck.
You can fix it like this:

#pragma once
class Vector;
class AbstractFigure
{
public:
  virtual void Scale() = 0;
  virtual void Rotate() = 0;
  virtual void Move(const Vector& direction) = 0;
};