qsort - sorts an array
void qsort( void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
The qsort() function sorts an array with nmemb
elements of size size. The base argument
points to the start of the array.
The contents of the array are sorted in ascending order
according to a comparison function pointed to by
compar, which is called with two arguments that point
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. If two members compare as equal,
their order in the sorted array is undefined.
The qsort() function returns no value.
SVID 3, POSIX, BSD 4.3, ISO 9899