C2061 - Circular dependency

Question

How to avoid circular dependency on these code:

Mechanic.cpp:

#include "stdafx.h"
#include "Characters.h"
#include "Monsters.h"

using namespace characters;
using namespace monsters;
using namespace std;

void character::character_atack(character const cha, monster &monst)
{
    if (cha.dexterity + k(20) >= monst.defense)
        monst.health = monst.health - cha.strength;
}
int k(int const max)
{
    return (rand() % max);
}
void monster::monster_atack(character &cha, monster const monst)
{
    if (monst.atack + k(20) >= cha.dexterity)
        cha.health = cha.health - monst.damage;
}

Monsters.h:

#include <iostream>
#include <string>

namespace monsters
{
    using namespace std;

    class monster{
    protected:
        string name;
    public:
        int atack;
        int damage;
        int health;
        int defense;

        monster(int atk, int dmg, int hp, int def) : atack(atk), damage(dmg),
                health(hp), defense(def) {}
        ~monster();

        void monster_atack(character &cha, monster const monst);
    };

    class greenskins:monster{
        greenskins(int atk, int dmg, int hp, int def) : monster(atk, dmg, hp, def) {}
    };
}

Characters.h:

#include <iostream>
#include <string>
#include <vector>

namespace characters
{
    using namespace std;

    class character{
    protected:
        int level;
        int experience;
        string name;
    public:
        int health;
        int strength;
        int intelligence;
        int dexterity;

        struct position{
            int x;
            int y;
        }pos;

        character(int str, int in, int dex) : strength(str), intelligence(in),
                dexterity(dex), level(1), experience(0) { 
            cout << "What's your name?" << endl;
            cin >> name; }
        ~character();

        void info_character();
        void character_atack(character const cha, monster &monst);
    };
}

The compilator gives me errors like this:

Error   1   error C2061: syntax error : identifier 'monster' 

or

Error   9   error C2511: 'void monsters::monster::monster_atack(characters::character &,const monsters::monster)' : overloaded member function not found in 'monsters::monster'

Answer 1

The issue is that character has a function that takes a monster& and monster has a function that takes a character&, but you don't declare the other class in either case. Thankfully, since you just pass the classes as arguments in both places (as opposed to having them be members or something), it is sufficient to forward-declare both classes in both places:

// in character.h
namespace monsters {
    class monster; // just fwd-declare
}

namespace characters {
    class character {
        // as before
    };
}

And similar in the other file.

[update] Also, you're just referencing monster inside of class character in the header file, you need to qualify it as monsters::monster.

Answer 2

The first error comes from the following line in Characters.h

void character_atack(character const cha, monster &monst);

You include Characters.h into your .cpp file before you include the Monsters.h and thus the type monster is not yet known. To fix this, change your Characters.h to look like this:

... //includes
namespace monsters {
  class monster;
}

namespace characters {
   class character {
        ... //class definition   
   }
}

---

The second error is a not matching signature. You are declaring following method:

 void monster_atack(character &cha, monster const monst)

but defining

 void monster::monster_atack(character &cha, const monster monst)

At least that is what the compiler said.

I would suggest to change the signature to:

void monster_atack(character &cha, const monster& monst)

to prevent needless copy operations. (depending on optimization of course)