Visual Studio error C2061: syntax error: identifier

Question

//Species.h
#pragma once
#include <iostream>
#include <string>
using namespace std;
class Species
{
protected:
    int HP, GroundAttack, AirAttack, MoveMode;
public:
};

// Protoss.h
#pragma once
#include "Species.h"
#include "Terran.h"

class Protoss : public Species
{
protected:
    int PS;
public:
    virtual void Input();
    virtual void Output();
    void B_AbilityAttack_A(Terran *);
};

// Terran.h
#pragma once
#include "Species"
#include "Protoss.h"

class Terran : public Species
{
public:
    virtual void Input();
    virtual void Output();
    void A_AbilityAttack_B(Protoss *);
};

"error C2061: syntax error : identifier 'Terran'"

"error C2061: syntax error : identifier 'Protoss'"

error in: void A_AbilityAttack_B(Protoss *) and void B_AbilityAttack_A(Terran *)

How to fix it?

After fix In a method of class Protoss, I wrote:

void Protoss::B_AbilityAttack_A(Terran *x)
{
    if (this->AbilityAttack() == 0 && x->GetMoveMode() == 0)
    {
        x->SetHP(x->GetHP() - this->GAttack());
    }
    else if (this->AbilityAttack() == 1 && x->GetMoveMode() == 0)
    {
        x->SetHP(x->GetHP() - this->GAttack());
    }
    else
    {
        x->SetHP(x->GetHP() - this->AAttack());
    }
}

And error in x : "pointer to incomplete class type is not allowed"

So how to fix it?

Answer 1

You have a circular dependency. Remove the include of Protoss by Terran and vice versa, the use forward declarations instead.

// Protoss.h
#pragma once
#include "Species.h"

class Terran;
class Protoss : public Species
{
protected:
    int PS;
public:
    virtual void Input();
    virtual void Output();
    void B_AbilityAttack_A(Terran *);
};

// Terran.h
#pragma once
#include "Species"

class Protoss;
class Terran : public Species
{
public:
    virtual void Input();
    virtual void Output();
    void A_AbilityAttack_B(Protoss *);
};

This will work because you don't need the full class definitions because the arguments are pointers, you just need to forward declare them.