Question

I am trying to compile this code:

class OthelloState {
public: // constructor 

    Othello(int r, int c);

/* other stuff */

private: // private data

    const int rows;

    const int columns;

    int board[rows][columns];
}

I keep ending up with:

OthelloState.h:109: error: invalid use of non-static data member 'OthelloState::rows'
OthelloState.h:115: error: from this location
OthelloState.h:115: error: array bound is not an integer constant
OthelloState.h:112: error: invalid use of non-static data member 'OthelloState::columns'
OthelloState.h:115: error: from this location
OthelloState.h:115: error: array bound is not an integer constant

I assume that this means I have to make rows and columns static. But if I make them static, I cannot initialize either with from a constructor, the way I have to for this project…

Is there some other way I can do this?

PS: I know that in real Othello, the board is a square 8 by 8 grid…But after considering how long it would take the computer to generate the next best move on a partial 8 by 8 grid, we are not going to play with “real” Othello board (i.e. no predefined board sizes).

Answer 1

In C++, variable length arrays are not allowed. board[][] needs to know both of its dimensions at compile time. You can use vector<vector<int> > board;, if you want to initialize row and col at runtime.

class OthelloState {
public:
    OthelloState(int r, int c);

private: // private data
    const int rows;  // should be 'unsigned int'
    const int columns;

    vector<vector<int> > board;  
};

Other solution:

Suppose you know rows and cols at compile time then you can use template. That is as good as initializing row and col in constructor.

template<unsigned int row, unsigned int col>
class OthelloState {
public:
...
private:
  int board[row][col];
};

Usage:

  OthelloState<8,8> obj;
  OthelloState<10,10> obj;