How do I define two C++ classes with pointers to each other?

I'm trying to make two classes that hold a pointer or variable of the other, like this (pseudo-code):
---unit.h---

Code:

---

#ifndef UNIT_H
#define UNIT_H
#include "action.h"
#include <vector>
using namespace std;

class Unit {
  vector<Action> actions;
  int hp;
};
#endif

---

---action.h---

Code:

---

#ifndef ACTION_H
#define ACTION_H
#include "unit.h"

class Action {
  Unit *target_unit;
  int action_type;
};
#endif

---

But since one is defined inside the other, it can't compile the program. It reads in action.h and sees unit.h is included, when it read unit.h, it says Action is not defined. Is there a way around error?

You can use a forward declaration:

Code:

---

#ifndef ACTION_H
#define ACTION_H

class Unit;

class Action {
  Unit *target_unit;
  int action_type;
};
#endif

---

you do a forward reference.

Code:

---

#ifndef UNIT_H
#define UNIT_H
class Action;
#include <vector>
using namespace std;

class Unit {
  vector<Action*> actions;
  int hp;
};
#endif

---

Code:

---

#ifndef ACTION_H
#define ACTION_H
class Unit;

class Action {
  Unit *target_unit;
  int action_type;
};
#endif

---

notice that the vector now has a pointer to Action.
the include will go into the cpp file.

kroiz, why do you recommend that the vector should store Action pointers?

Thanks for the fast replies.

Quote:

---

Originally Posted by laserlight

kroiz, why do you recommend that the vector should store Action pointers?

---

I think that if it is not a pointer then he can not use forward reference it must use include.
I am pretty sure. Am I wrong?

Quote:

---

I think that if it is not a pointer then he can not use forward reference it must use include.
I am pretty sure. Am I wrong?

---

You are right, but the Action class has a Unit* member variable, so the forward declaration can be used there and action.h can continue to be included in unit.h, requiring no change to the vector.

yes ofcourse you are right.
I was in such a hurry to post first because it is my first reply to someone on the forum that I missed the details.
and you beat me to it after all.
not fair )-:

Haha, no worries, I lost a "fastest finger first" reply race recently to two people :)

Quote:

---

Originally Posted by kroiz

I think that if it is not a pointer then he can not use forward reference it must use include.
I am pretty sure. Am I wrong?

---

You're sort of wrong. Forward declarations can be used with references too.

I did not know that,That is good to know.
thanks.