康威的生命游戏问题更新板

Question

So I'm working on an assignmmnet for school which involves writing this update function in assembly to work with C code given to us. It's just a simple version of Conway's Game of Life which generates a random board configuration and then updates it with new values based on the rules. I figured I would write the function in C first so I knew what to do in assembly. I'm running into some difficulty which I think stems from not fully understanding how double pointers work in C. Some where in the code given to us the board for the Game of Life is initialized using malloc calls like this:

int **board;
board = malloc(sizeof(int *) * height);
for(i = 0; i < height; i++){
    board[i] = malloc(sizeof(int) * width);
}

Each cell is either given a 1 if alive or a 0 if it's dead.

Now our update function we're supposed to write takes **board as a parameter. I've only worked with a regular 2 dimensional array but if I'm understanding it correctly than this double pointer should behave similarly to a 2 dimensional array. Anyway here's the c code I have written:

void update(int **board, int width, int height)
{
int neighborCount = 0; //keeps count of live neighbors
int row = 0;
int col;

int tempBoard[height][width]; //holds updated board temporarily

for(; row < height; row++)
{
    col = 0;

    for(; col < width ; col++)
    {
        //If tests to check if out of bounds.  If not than adds value of cell
        //to neighbor count.  Continues for each possible neighbor
        if ((row - 1) >= 0 && (col - 1) >= 0)
        {
            neighborCount = neighborCount + board[row - 1][col - 1];
        }
        if ((row - 1) >= 0)
        {
            neighborCount = neighborCount + board[row - 1][col];
        }
        if ((row - 1) >= 0 && (col + 1) < width)
        {
            neighborCount = neighborCount + board[row - 1][col + 1];
        }
        if ((col - 1) >= 0)
        {
            neighborCount = neighborCount + board[row][col - 1];
        }
        if ((col + 1) < width)
        {
            neighborCount = neighborCount + board[row][col + 1];
        }
        if ((row + 1) < height && (col - 1) >= 0)
        {
            neighborCount = neighborCount + board[row + 1][col - 1];
        }
        if ((row + 1) < height)
        {
            neighborCount = neighborCount + board[row + 1][col];
        }
        if ((row + 1) < height && (col + 1) < width)
        {
            neighborCount = neighborCount + board[row + 1][col + 1];
        }

        //save new value in temp board based on neighbor count
        if (board[row][col] == 1)
        {
            if (neighborCount == 2 || neighborCount == 3)
            {
                tempBoard[row][col] = 1;
            }
            else
            {
                tempBoard[row][col] = 0;
            }
        }
        else
        {
            if (neighborCount == 3)
            {
                tempBoard[row][col] = 1;
            }
            else
            {
                tempBoard[row][col] = 0;
            }
        }

        neighborCount = 0;
    }
}

//update board with new values from temp board
for(; row < height; row++)
{
    for(; col < width ; col++)
    {
        board[row][col] = tempBoard[row][col];
    }
}

}

My issue is towards the end of the function where I'm trying to update the values in **board with the new values I saved in tempBoard. I'm sure it's my lack of understanding of double pointers but I can't figure out why when the board reprints itself after returning from my function it's identical to it's original state. I'm guessing I'm only be updating the local copy of **board and I'm losing my changes when I exit my function but I'm completely lost on how I should go about making sure my changes are seen outside of this function.

Any help would be greatly appreciated, I've been trying my best to figure it out on my own but I'm just stuck right now on what to do. If you need anymore info from me just let me know.

Answer 1

row and col are being used in two different loops, and their values aren't being reset in between loops. So when you go to copy the temp board to the main board, row already equals height and the loop breaks immediately.

Just do this:

//update board with new values from temp board
for(row = 0; row < height; row++)
{
    for(col = 0; col < width ; col++)
    {
        board[row][col] = tempBoard[row][col];
    }
}