聲明為另一個類的朋友的類的方法引發錯誤

Question

我有以下兩個類Player和FriendOfPlayer ：

播放器.hpp

#ifndef PLAYER
#define PLAYER

#include"FriendOfPlayer.hpp"
#include<string>


using namespace std;

//class FriendOfPlayer;

class Player{

    public:

           // getters and setters ...

        static int getNbObj(){
            return nbObj;
        };

        friend void FriendOfPlayer::displayPlayerPrivateMember(Player &p);
        

        // constructor
        Player();
        Player(string name= "None", int health = 0, int xp = 0);
        Player(const Player &source);


        // Destructor
        ~Player(){
            --nbObj;
        };


    private:
        //private members not displayed
        string privMember = "private member";
        static int nbObj;

       
};

#endif

播放器.cpp

#include "Player.hpp"
#include<string>

using namespace std;


Player::Player(){;};

Player::Player(string name, int health, int xp)
    : name{name}, health{health}, xp{xp}{
        ++nbObj;
    }

Player::Player(const Player &source)
        : name{"I am a copy"}, health{source.health}, xp{source.xp}{
            ++nbObj;
        }


int Player::nbObj = 0;

玩家之友.hpp

#ifndef FRIEND_OF_PLAYER
#define FRIEND_OF_PLAYER

#include"Player.hpp"

class FriendOfPlayer {

    public:

        void displayPlayerPrivateMember(Player &p);


};

#endif

玩家之友.cpp

#include "Player.hpp"
#include "FriendOfPlayer.hpp"


#include<iostream>
#include<stdio.h>


void FriendOfPlayer::displayPlayerPrivateMember(Player &p){

    cout << p.privMember << endl;
}

但是，在編譯此代碼時，我得到：

g++ Player.cpp FriendOfPlayer.cpp
FriendOfPlayer.cpp:9:6: error: prototype for ‘void FriendOfPlayer::displayPlayerPrivateMember(Player&)’ does not match any in class ‘FriendOfPlayer’
 void FriendOfPlayer::displayPlayerPrivateMember(Player &p){
      ^~~~~~~~~~~~~~
In file included from Player.hpp:5:0:
FriendOfPlayer.hpp:10:14: error: candidate is: void FriendOfPlayer::displayPlayerPrivateMember(int&)
         void displayPlayerPrivateMember(Player::Player &p);

我究竟做錯了什么？ 原型void FriendOfPlayer::displayPlayerPrivateMember(int&)來自哪里？

Answer 1

我想知道為什么您沒有遇到標題包含問題。 你不能像你那樣做一個循環包含。 我建議從您的 Friendofplayer.hpp 中刪除#include "player.hpp 。而只是在 Friendofplayer.hpp 中向前聲明 Player 類。

編輯：您收到的錯誤消息令人困惑，但我只是自己嘗試過，循環依賴是導致錯誤的原因。 前向聲明解決了這個問題。 在此處嘗試最小示例。