C++ 对象共享错误 LNK2005 和 LNK 1169

Question

我目前正在尝试创建一个由玩家共享的棋盘对象上的玩家类创建的两个玩家对象轮流玩的井字游戏。据我所知，我已经完成了这个程序，但是当我尝试构建时，我遇到了这些错误并且似乎无法找到原因。我对面向对象编程比较陌生。这是我得到的错误:

 1>Player.obj : error LNK2005: "public: __thiscall Player::Player(class Board *,char)" (??0Player@@QAE@PAVBoard@@D@Z) already defined in Connect_Four_Game.obj
 1>fatal error LNK1169: one or more multiply defined symbols found

代码如下:

#ifndef ___PLAYER_H___
#define ___PLAYER_H___


#include <iostream>
#include "Board.h"
using namespace std;
class Player {
private:
    Board * sharedboard;
    char player_char;
public:

    Player(Board *shared_board, const char player_char);

    bool play(int &choice);
    bool wins();
    bool columnFull(int&choice);

};
Player:: Player(Board *shared_board,const char player_char)
    : player_char(player_char), sharedboard(shared_board)
{}

#endif

板头文件:

#ifndef ___BOARD_H___
#define ___BOARD_H___


#include <iostream>
#include <vector>
using namespace std;

class Board {

public:
    vector<vector<char>> holder;
    void displayBoard();
    bool isBoardFull();
    Board()
    {
        vector<vector<char>>holder(7, vector<char>(7, 'A'));
    }
};


#endif

播放器cpp文件:

#include <iostream>
#include "Player.h"

using namespace std;


bool Player::columnFull(int &choice)//DONE
{
    for (int i = 6; i >= 0; i--)
    {
        if(sharedboard->holder[i][choice]=='A')//if the choice is not full
        {
            sharedboard->holder[i][choice] = player_char;//put the players character(X or O here)
            return false;
        }
        else//if the choive is full
        {

            return true;
        }
    }
}

bool Player::play(int &choice)//DONE
{ 
    if(choice < 0 )
    {
        cout << "Choice is not valid." << endl;
        return false;
    }
    else if(choice > 6)
    {
        cout << "Choice is not valid." << endl;
        return false;
    }
    else if(columnFull( choice))//if its true then its full
    {
        cout << "Choice is not valid." << endl;
        return false;
    }
    else
    {
        sharedboard->displayBoard();//if previous ones were false, then the place was empty, and filled, therefore the board will be displayed
    }
}

bool Player::wins()//if the player wins
{

        int o = 0;
        int x = 0;

        for (int i = 0; i < 7; i++)//HORIZONTAL
        {
            for (int j = 0; j < 7; j++)
            {
                if (sharedboard->holder[i][j] == 'O')
                {
                    o++;
                }
                else if (sharedboard->holder[i][j] == 'X')
                {
                    x++;
                }
                if (o == 4)//if O is four horizantily
                {
                    cout << "Player2 wins!" << endl;
                    sharedboard->displayBoard();
                    return true;
                }
                else if (x == 4)//if X is four horizantily
                {
                    cout << "Player1 wins!" << endl;
                    sharedboard->displayBoard();
                    return true;
                }
            }
        }//HORIZONTAL
        o = 0;
        x = 0;
        for (int i = 0; i < 7; i++)//VERTICALLY
        {
            for (int j = 0; j < 7; j++)
            {
                if (sharedboard->holder[j][i] == 'O')
                {
                    o++;
                }
                else if (sharedboard->holder[j][i] == 'X')
                {
                    x++;
                }
                if (o == 4)//if O is four vertically
                {
                    cout << "Player2 wins!" << endl;
                    sharedboard->displayBoard();
                    return true;
                }
                else if (x == 4)//if X is four vertically
                {
                    cout << "Player1 wins!" << endl;
                    sharedboard->displayBoard();
                    return true;
                }
            }
        }//VERTICALLY
}

开发板cpp文件:

#include "Board.h"
#include<iostream>

using namespace std;

void Board::displayBoard()//DONE
{
    for (int i = 0; i < 7; i++)
    {
        for (int j = 0; j < 7; j++)
        {
            cout << holder[i][j] << " ";
        }
        cout << endl;
    }
}
bool Board::isBoardFull()//DONE-CORRECTED
{
    for (int i = 0; i < 7; i++)
    {
        for (int j = 0; j < 7; j++)
        {
            if (holder[i][j] == 'A')
            {
                return false;//game continues
            }
            else if(((i==6)&&(j==6)))
            {
                return true;//ends in tie
            }
        }
        cout << endl;
    }
}

主要源文件:

#include<iostream>
#include<string>
#include "Board.h"
#include "Player.h"

using namespace std;

int main()
{
    Board myBoard = Board();


    /* 
       //Create your player objects based on your choice of approach to share an object.
       //The parameters "..." are left for you to set.
       Player player1 = Player(...); 
       Player player2 = Player(...);
    */
    Player player1(&myBoard, 'X');
    Player player2(&myBoard, 'O');


    int col, turn = 0;
    bool continueGame = true;
    bool validMove = false;

    while(continueGame)
    {
        myBoard.displayBoard();
        if(turn == 0)
        {
            cout << "Player 1 turn: " << endl;
            cin >> col;
            validMove = player1.play(col);

            if(player1.wins())
            {
                continueGame = false;
                cout << "Player1 won the game!" << endl;
            }
        }
        else if(turn == 1)
        {
            cout << "Player 2 turn: " << endl;
            cin >> col;
            validMove = player2.play(col);

            if(player2.wins())
            {
                continueGame = false;
                cout << "Player2 won the game!" << endl;
            }
        }

        if(continueGame) {
            //If a valid move has been done, change the turn
            if(validMove) {
                turn = (turn + 1) % 2;      
            }

            if(myBoard.isBoardFull())
            {
                continueGame = false;
                cout << "Noone won the game!" << endl;
            }
        }
    }   

    cout << "Game is over!" << endl;
    cout << "Final state of the board: " << endl;
    myBoard.displayBoard();

    return 0;
}

我没有发布整个播放器 cpp 文件，因为它大约有 600 行，只有对角线搜索的重复，没有其他内容。现在谢谢你。

Answer 1

错误提示您定义了多个符号。很可能，您在其他一些文件中多次(直接或间接)包含了 Player.cpp 文件(而不是 Player.h)(您没有共享 Connect_Four_Game 文件)。

我建议您做一些研究:如果包含 .cpp 文件会发生什么情况？阅读声明、定义、多重包含……。这也可能有用: Already defined in .obj - no double inclusions

我一开始和你一样，问了不好的问题(我想每个人都这样)。下次，您应该尝试检测链接器错误发生的位置，并知道什么是链接器错误。

我清楚地记得我开始使用 C++ 的日子。由于您显然为此代码付出了努力，请允许我给您一些与您发布的代码相关的建议。

设计

在编码之前，做好设计。可以在玩家之间共享一个棋盘。您还可以拥有玩家订阅的看板。无论哪种方式:

Board 应该知道关于它自己的一切。也就是说:玩家不应该访问棋盘的“holder”属性来查看一个方格是否被占用。玩家应该直接问棋盘:那个方格是空的吗？

同理，columnFull 不应该是 Player 的方法。

代码

您应该尝试使用现代 C++。我重写了您的一些代码。

播放器构造函数:使用智能指针

Player(const std::shared_ptr<Board>& board, std::string&& name) : 
    m_name(std::move(name)), m_board(board)
{}

你的主文件现在看起来像这样:

std::shared_ptr<Board> myBoard = std::make_shared<Board>();
Player me(myBoard,"Me");
Player you(myBoard,"You");

引用内置类型:

bool play(const int choice) // no reference to built-in types unless needed

尽可能使用常量:

bool wins() const // should be const, you don't want to modify "this"

使用私有(private)成员、字符串而不是字符和智能指针

private:
    std::shared_ptr<Board> m_board; // use smart pointers
    std::string m_name; // not playerChar -> it's obvious its about the player

看看现代 C++ 有多好:

void display() const // use const if you don't modify this
{
    // you had hardcoded numbers here (7)... try to avoid that, keep the code generic
    for (const auto& v : m_holder) // you do have access to C++11 I hope?
    {
        for (const auto& h : v)
            std::cout << h << std::endl;
    }
}

使用标准库:

bool isFull() const // try to use the wonderful standard library, your code will be much more readable
{
    for (const auto& v : m_holder)
    {
        auto it = std::find_if(v.begin(),v.end(),[](const std::string& h){ return h.empty(); });
        if (it==v.end())
            return false;
    }
    return true;
    // cout << endl shouldn't be in this function which checks if the board is full...
}

也许一些 typedef 来保持代码干净？此外，使用 _ 或 m_ 作为属性。尽可能将属性保密。

private: // try to keep members in private so you control who changes them
    // maybe use typedef? you use that type multiple times
    typedef std::vector<std::vector<std::string>> HolderType;
    HolderType m_holder; // for members, use _ or m_

总体

1. 在编码之前专注于设计。
2. 使用现代 C++、标准库...
3. 使用智能指针。
4. 了解何时使用常量、引用...
5. 保持代码整洁。

这当然是一个非常不完整的建议列表。但这些是您的代码的主要缺陷。

我希望这对您有所帮助。