c++ - 如何将二维数组作为只读传递给双指针函数？

Question

我需要传递指向二维数组第一个元素的双指针，以防止函数修改二维数组中的任何元素的方式起作用。我以为我可以用 const reference - int** const &board 来做到这一点，但它并没有像我预期的那样工作。此外，二维数组不能声明为 const，因为它应该可以在该函数之外修改。这样的功能怎么可能？这是我在其中使用它的有效简化代码:

#include <iostream>

class player
{
public:
    player(){}
                                 // returns player move
    int move(int** const &board)
    {
        board[1][1] = 9; // should be illegal
        return 9;
    }
};

class game
{
    int** board;    
    player *white, *black;

public:
    game(player* player1, player* player2): white(player1), black(player2)
    {
        int i, j;

        board = new int* [8];

        for(i = 0; i < 8; i++)
        {
            board[i] = new int [8];
            for(j = 0; j < 8; j++)
                board[i][j] = 0;
        }
    }
                // gets moves from players and executes them
    void play() 
    {
        int move = white->move(board);

        board[2][2] = move; // should be legal
    }
                 // prints board to stdout
    void print() 
    {
        int i, j;

        for(i = 0; i < 8; i++)
        {
            for(j = 0; j < 8; j++)
                std::cout << board[i][j] << " ";
            std::cout << std::endl;
        }
    }

};

int main()
{
    game g(new player(), new player());

    g.play();
    g.print();
}

Answer 1

我看了你的代码，有趣的部分是:

int move(int** const &board)
{
    board[1][1] = 9; // should be illegal
    return 9;
}

如果您希望 board[1][1] = 9 是非法的，那么您必须将参数声明为:

int move(int const** &board);
//int move(int** const &board); doesn't do what you want

有一个区别:int** const 不会将数据设为只读。查看第二个链接中的错误:

• http://www.ideone.com/mnKc9 (演示 int** const)
• http://www.ideone.com/BOvUL (演示 int const**)

如果将参数写成这样会更好:

int move(int const* const * const &board);

因为这使得所有内容都为常量:那么以下所有赋值都是非法的:

board[1][1] = 9;  //illegal
board[0] = 0;     //illegal
board = 0;        //illegal

在此处查看错误:http://www.ideone.com/mVsSL

现在一些图表:

int const* const * const
    ^       ^       ^
    |       |       |
    |       |       |
    |       |       this makes board = 0 illegal
    |        this makes board[0] = 0 illegal
    this makes board[1][1] = 9 illegal