circular includes?

**Raybdbomb** · 02-25-2006

I'm doing work and I think the trouble I'm having is with circular includes.

I have Unit as a base class, and Hero and Army both derive from Unit.
Hero needs to have a vector of Army*'s, and Army needs to have a single Hero*. Here is how the code is setup:

Code:

#ifndef ARMY_H
#define ARMY_H

#include "Unit.h"
#include "Hero.h"

using namespace std;

class Army : public Unit
{
public:
	Hero* getHero(){return phero;}
	void setHero(Hero *theHero){phero = theHero;}

private:
	Hero *phero;
// ... etc

and

Code:

#ifndef HERO_H
#define HERO_H

#include<iostream>
#include "Army.h"
#include <string>
#include<vector>

using namespace std;

class Hero : public Unit
{
public:
	void addArmy(Army*);
	void removeArmy(Army*);
private:
	vector<Army*> army;
// ... etc

But when it's trying to compile Hero, it sees that Army is included, so it tries to compile that, which says that Hero is included, etc. So I believe I've reached a circular include.

Is there any way to achieve this functionality without doing a restructure of my classes? Thanks for help.

**Raybdbomb** · 02-25-2006

nevermind, i found a way through in intermediary class

**grumpy** · 02-25-2006

Intermediary class is one way. You might also want to do a search for "forward declaration".

**7stud** · 02-25-2006

How do you declare an object when two classes have pointers to each other?

**Dave_Sinkula** · 02-25-2006

Originally Posted by 7stud

How do you declare an object when two classes have pointers to each other?

Often a forward declaration is used.

**7stud** · 02-25-2006

declare a class <---->declare an object.

How do you declare an object of one of the classes in main()?

Code:

#include <iostream>
using namespace std;

using namespace std;

class B;

class A
{
public:
	A(B* ptr, int n)
	{
		pB = ptr;
		num = n;
	}

	int get()
	{
		return num;
	}

private:
	B* pB;
	int num;
};

class B
{
public:
	B(A* ptr, int n)
	{
		pA = ptr;
		num = n;
	}

	int get()
	{
		return num;
	}
private:

	A* pA;
	int num;
};


int main()
{
	

    return 0;
}

Do you have to use a default constructor?

**Dave_Sinkula** · 02-25-2006

Originally Posted by 7stud

How do you declare an object when two classes have pointers to each other?

I guess define might have been a better term.

Declare a class; define an object.

If one has to exist before the other, and it needs to point to something that may not yet exist, I'd say that a default constructor should be necessary for at least one of the them. But perhaps it depends on the scope of the objects.

Code:

#include <iostream>
using namespace std;

class B;

class A
{
   B* pB;
public:
   A(B* ptr) : pB(ptr) {}
   friend ostream& operator<< (ostream& o, const A &a)
   {
      return o << a.pB;
   }
};

class B
{
   A* pA;
public:
   B(A* ptr) : pA(ptr) {}
   friend ostream& operator<< (ostream& o, const B &b)
   {
      return o << b.pA;
   }
};

extern B b;
A a(&b);
B b(&a);

int main()
{
   cout << a << endl;
   cout << b << endl;
   return 0;
}

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