void qsort(void *__base, size_t __nmemb, size_t __size, __compar_fn_t
__compar)
The qsort() function is a modified partition-exchange sort, or quicksort.
The qsort() function sorts an array of
nmemb objects, the initial member of which is pointed
to by base. The size of each object is specified by
size. The contents of the array base are sorted in
ascending order according to a comparison function pointed to by
compar, which requires two arguments pointing to the
objects being compared.
The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.