错误C2079：我该如何处理？

Question

当我尝试在player.h中加入battlefield.h时，会发生此错误：
error C2079: 'BattleField::firstplayer' uses undefined class 'Player'.
真的不明白为什么会发生这种情况，我通过网络搜索过，看到了圆形图案问题，但这对我来说并不是很清楚。任何帮助，将不胜感激。

Player.h：

#include <iostream>
#include <fstream>

#ifndef PLAYER_H
#define PLAYER_H

#include "classDeck.h"

class Player
{
private:

    char* Name;
    double Health;
    double Energy;

public:
    Deck playerdeck;

    Player();
    Player( char* Name, double Health, double Energy );
    Player( const Player& play );
    Player& operator= ( const Player & play );
    ~Player();

    void set_Name( char* Name );
    void set_Health( double val );
    void set_Energy( double val );
    void print_Player()const;

    char* get_Name()const
    {
        return Name;
    }

    double get_Health()const
    {
        return Health;
    }

    double get_Energy()const
    {
        return Energy;
    }



};

#endif

battleField.h：

    #include <iostream>
#include <fstream> 

#ifndef BATTLEFIELD_H
#define BATTLEFIELD_H

#include "classDeck.h"
#include "Player.h"
class BattleField
{

private:

    Deck firstPlayer;    //TESTE NA PURVI IGRACH
    Deck secondPlayer;   //TESTE NA VTORI IGRACH
    Deck semetary;     //MASIV Grobishte

    Player firstplayer1;
    Player secondplayer2;

public:

    Deck playedCards; //MASIV OT IZIGRANI KARTI

    BattleField();  // PODRAZBIRASHT SE KONSTRUKTOR
    ~BattleField(); //DESTRUKTOR
    BattleField( const BattleField& battle ); // KOPIRASHT KONSTRUKTOR
    BattleField& operator= ( const BattleField& battle ); //OPERATOR =

    void insertLeftPlayDeck(const Deck& deck);  // ZADAVAME TESTE NA EDINIQ IGRACH
    void insertRightPlayDeck(const Deck& deck); //ZADAVAME TESTE NA DRUGIQ IGRACH

    void Battle(); //FUNKCIQ, V KOQTO DVE KARTI SE BIQT
    void display(); //PRINTIRASHTA FUNKCIQ
    void Serializer(); //SERIALIZIRASHTA
    const Deck get_semetary() const;
    const Deck get_playedCards()const;
    const Deck get_firstPlayer() const;
    const Deck get_secondPlayer() const;

};
#endif