Two-dimensional dynamic array pointer access

Question

p = (int *)malloc(m * n * sizeof(int));

If I use p as a two-dimensional dynamic array, how do I access the elements inside?

Answer 1

If you can rely on your C implementation to support variable-length arrays (an optional feature), then a pretty good way would be to declare p as a pointer to (variable-length) array instead of a pointer to int:

int (*p)[n] = malloc(m * sizeof(*p));  // m rows, n columns

Then you access elements using ordinary double indexes, just as if you had declared an ordinary 2D array:

p[0][0] = 1;
p[m-1][n-1] = 42;
int q = p[2][1];

Most widely used C implementations do support VLAs, but Microsoft's is a notable exception.