How to sort a multidimensional array by qsort function from #cstdlib?

Question

For example
{{1,6},{2,3},{3,8},{4,0}} -> {{4,0},{2,3},{1,6},{3,8}}
Now it's sorted by 1 index
How to write a comparator for this?

Comparator for a simple array
int compare(const void * x1, const void * x2){
return (*(int*)x1-*(int*)x2);
}
I'm not sure at all how it works

Answer 1

int comp(const void *x1, const void *x2)
{
return *((int*)x1+1) > *((int*)x2+1) ;
}

int arr[][2] = {{1,6}, {2,3}, {3,8}, {4,0}};

qsort(arr, 4, sizeof arr[0], comp);