Question

I have the next struct

struct Board
{
    int width;
    int height;
    char **board;
}

And I would like to expand the **board, meaning I need more memory and thus the call to
realloc(). So my question is how do I do that – should I call realloc() on every line in the array separatly and the call it on the entire struct?
Thanks!

Answer 1

You need to call malloc not realloc on board. When you instantiate an object of Board, no memory is allocated to the member board ; so it’s not a question of reallocating memory, but allocating memory to board in the usual way for multidimensional arrays.

#include <stdlib.h>

int **array;
array = malloc(nrows * sizeof(int *));
if(array == NULL)
    {
    fprintf(stderr, "out of memory\n");
    exit or return
    }
for(i = 0; i < nrows; i++)
    {
    array[i] = malloc(ncolumns * sizeof(int));
    if(array[i] == NULL)
        {
        fprintf(stderr, "out of memory\n");
        exit or return
        }
    }

Once, you’ve allocated memory, and then if you need to expand board (e.g. board was initially 2×2 and now you want it to be 6×6), call realloc in the same order you called malloc to initialize board.