康威生命游戏的ANSI C实现

Question

I am currently trying to learn the C language by implementing a console version of "Conway's Game of Life". I have a function called 'set_dead_state', which just create creating a 2d array of 0's:

void create_game_board(int *dest[], int width, int height) {
  for(int i = 0; i < height; i++) {
    dest[i] = malloc(sizeof(int)*width);
    memset(dest[i], 0, width*sizeof(int));
  }
}

Setting width and height to 10 , I loop through the array and print out each 0 as " - " using this function:

void print_game_board(int* board[], int width, int height) {
  for(int y = 1; y < height+1; y++) {
    for(int x = 1; x < width+1; x++) {
      if(board[y][x] == DEAD)
        printf(" - ");
      else
        printf(" # ");
    }
    printf("\n");
  }
}

It outputs as expected:

 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
 -  -  -  -  -  -  -  -  -  - 
memory freed successfully

And I free the memory I allocated in the create_game_board function using this function:

void free_array_memory(int *arr[]) { 
  for(int i = 0; i < sizeof(*arr)/sizeof(arr[0]); i++) 
    free(arr[i]);
}

My question is in regards to my first try at implementing the create_game_board function, which looked like this:

// This does not work.
void create_game_board(int* dest[], int width, int height) {
  for(int i = 0; i < height; i++) {
    int row[width]; 
    memset(dest, 0, width*sizeof(int));
    dest[i] = row;
  }
}

Below is what outputted to the console when I used this version of the function, in addition to the message I get when trying to free memory (width and height are the same values). I would've expected it to work like the one I mentioned at the beginning. Why doesn't this function work?

 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
 -  -  -  -  -  -           - 
free(): invalid pointer
exited, aborted

Answer 1

In your earlier implementation, you set the pointers in src to the address of the first element of row . But - row is a variable on the stack, not on the heap; it gets "de-allocated" when the stack is popped (and used by other functions as part of the stack area). You can't free() that address.

However, both implementations are problematic:

• A function which "sets state" should not allocate memory; that's surprising (breaks the principle of least astonishment ). You could call the function create_game_board() or something.
• There's no good reason to make height different allocations. Just allocate width*height elements once, and set src elements to point into different points in that region.
• src is a poor choice of name for the game board row pointers parameter. It's not the "source" of anything.
• Why does your comment say the board is 10x10 when its size is dynamic?
• Is the board rectangular or square? If it's square, use the same variable name for both the width and the height (eg 'dimension' or 'order' or something).