Fastest way to zero out a 2d array in C?

Question

I want to repeatedly zero a large 2d array in C. This is what I do at the moment:

// Array of size n * m, where n may not equal m
for(j = 0; j < n; j++)
{
    for(i = 0; i < m; i++)
    {  
        array[i][j] = 0;
    }
}

I've tried using memset:

memset(array, 0, sizeof(array))

But this only works for 1D arrays. When I printf the contents of the 2D array, the first row is zeroes, but then I got a load of random large numbers and it crashes.

Answer 1

memset(array, 0, sizeof(array[0][0]) * m * n);

Where m and n are the width and height of the two-dimensional array (in your example, you have a square two-dimensional array, so m == n).