qsort - quicker sort
qsort(base, nel, width, compar)
size_t nel, width;
Qsort is an implementation of the quicker-sort algorithm. The
first argument is a pointer to the base of the data; the second is
the number of elements; the third is the width of an element in
bytes; the last is the name of the comparison routine to be called
with two arguments which are pointers to the elements being
compared. The routine must return an integer less than, equal to,
or greater than 0 according as the first argument is to be
considered less than, equal to, or greater than the second.
The comparison routine may not itself call qsort.