Comparer, a function that compares two elements.

The function shall follow this prototype

int comparer(const void *elem1, const void *elem2);

The function must accept two parameters that are pointers to elements, type-casted as void *. These parameters should be cast back to some data type and be compared.

The return value of this function should represent whether elem1 is considered less than, equal to, or greater than elem2 by returning, respectively, a negative value, zero or a positive value.