qsort() from An ANSI C Generic Algorithm

void qsort(	void *base,
		size_t nmemb,
		size_t size,
		int(*compare)(const void *, const void *));

where:	base	is a pointer to an array
	nmemb	is the number of elements in the array
	size	is the size of each array element
	compare	is a pointer to a function defined as:

			int compare(const void *e1, const void *e2);

			where:	e1 and e2 are elements pointers
			returns			if
				< 0		(*e1) <  (*e2)
				  0		(*e1) == (*e2)
				> 0		(*e1) >  (*e2)

		When subtraction is a valid operations for elements
		of type T, the compare funtion can be implemented as:

		{
			return (int)((*(T *)e1) - (*(T *)e2));
		}