Question

this is my first post on SO, even though i’ve spent some time already here.
I’ve got here a problem with a function returning a 2d array. I have defined a private 2d int array property int board[6][7] in my Game class, but i don’t know how to create a public getter for this property.

These are relevant parts of my game.h:

#ifndef GAME_H
#define GAME_H

class Game
{
public:
    static int const m_rows = 6;
    static int const m_cols = 7;

    Game();
    int **getBoard();

private:
    int m_board[m_rows][m_cols];

};

#endif // GAME_H

Now what I would like is something like this in game.cpp (cause I thought array name without brackets is a pointer to first element, obviously it doesn’t work with 2d arrays) :

int **Game::getBoard()
{
    return m_board;
}

So that i can put this for example in my main.cpp:

Game *game = new Game;
int board[Game::m_rows][Game::m_cols] = game->getBoard();

Can anybody help me, what should i put in my game.cpp ?

Thanks!

Answer 1

You cannot pass arrays by value into and out of functions. But there’s various options.

(1) Use a std::array<type, size>

#include <array>

    typedef std::array<int, m_cols> row_type;
    typedef std::array<row_type, m_rows> array_type;
    array_type& getBoard() {return m_board;}
    const array_type& getBoard() const {return m_board;}
private:
    array_type m_board;

(2) Use the correct pointer type.

    int *getBoard() {return m_board;}
    const int *getBoard() const {return m_board;}
private:
    int m_board[m_rows][m_cols];

An int[][] has no pointers involved. It isn’t a pointer to an array of pointers to arrays of integers, it’s an array of an array of integers.

//row 1               //row2
[[int][int][int][int]][[int][int][int][int]]

Which means one int* points to all of them. To get to a row offset, you’d do something like this:

int& array_offset(int* array, int numcols, int rowoffset, int coloffset)
{return array[numcols*rowoffset+coloffset];}

int& offset2_3 = array_offset(obj.getBoard(), obj.m_cols, 2, 3);