错误：“object”未在此作用域中声明

Question

我在c++是个新手，正在努力制造垄断游戏。不幸的是，它仍然在两个类之间的声明中显示了错误。我已经什么都试过了，真的不知道问题出在哪里。

错误：“Player”不在此范围内声明。

Engine.h

#ifndef ENGINE_H
#define ENGINE_H
#include "Player.h"
#include <vector>
using namespace std;
class Engine{
public:
    Engine(); // method that starts with game, take random number for getting number of players, set players to vector
    void play(); // method where players are playing.
    bool returnBalance(int a_money) const; // method that return True, if the players has still some amount on account, False otherwise
    bool isWinner();
    int setBalance(); // method that set curretn player amount
    void printWinner(); // method that print winter of the game
    void payBills(int amount); // player pay any bills with this method
    virtual ~Engine();
private:
    vector<Player*> players;
    int i_player;
    int balance;
    int currentPlayer;
};
#endif /* ENGINE_H */

Engine.cpp

#include "Engine.h"
#include <iostream>
#include <stdlib.h>
using namespace std;

Engine::Engine() {
    int numPlayers = rand()*(6-2)+2;
    for (int i = 0; i <= numPlayers; i++){
        Player* p = new Player;
        players.push_back(p);
    }
     cout << players.size() << endl; 

    int p_index = 0; 
     for(int i = 1; i <= players.size(); i++){
         p_index = i;
         p_index++;
         cout << p_index ;
     }
    currentPlayer = p_index;     

    cout << "Welcome to MonOOpoly game, the game will be played in the same order you already are." << endl;
}

void Engine::play() {
    do{

    }while(!isWinner());
}

bool Engine::isWinner(){
    int count = 0;
    for(int i = 1; i <= players.size(); i++){
        if(players[i]->getAmount() > 0)
            count++; 
    }
    if(count <= 1)
        return true;
    return false;

}

int Engine::setBalance(){
    int amount = players[currentPlayer]->amount;
    return players[currentPlayer]->amount;
}

bool Engine::returnBalance(int a_money) const{
    if (players[currentPlayer]->amount < a_money)
        return false;
    else 
        return true;
}

void Engine::payBills(int amount) {
    players[currentPlayer]->amount = players[currentPlayer]->amount - amount;
}

void Engine::printWinner() {
    int winner = 0;
    int newWinner = 0;
    for(int i = 1; i <= players.size(); i++){
        if(players[i] > 0){
            winner = players[i]->getAmount();
            if(newWinner < winner)
                newWinner = winner;
        }
    }
    cout << "Winner of the game MonOOpoly is: " << newWinner << endl;
}

Engine::~Engine() {
}

Player.h

#ifndef PLAYER_H
#define PLAYER_H
#include "Engine.h"
#include <string>
using namespace std;

class Player {
    friend class Engine;
public:
    Player(); // constructor
    int getAmount() const; // return how much of amount the player has yet
    void setAmount(int a); // set amount
    int getPosition() const; // return position of the player
    void setPosition(int p); // to set position
    virtual ~Player(); // destructor
private:
    int position; // the position of the player
    int amount; // the total amount
};


#endif /* PLAYER_H */

Player.cpp

#include <iostream>
#include <stdlib.h>
#include "Player.h"
using namespace std;

Player::Player() {
    amount = 5000;
    position = 0;
}

int Player::getAmount() const {
    return amount;
}

void Player::setAmount(int a) {
    amount = a;
}

int Player::getPosition() const {
    return position;
}

void Player::setPosition(int p) {
    position = p;
}

Player::~Player() {
}

Answer 1

您的头中有循环包含，可能会导致您正在看到的编译器问题。Engine.h包括Player.h和Player.h包括Engine.h

您应该：

• 将#include Player.h从Engine.h移动到Engine.cpp
• 在Engine.h (用class Player;)行中向前声明Player类。

前向声明在这里很有用，因为Engine.h只需要知道某个Player类的存在，而不是它的整个定义，因为它只是定义了指向该类的指针的简单向量。