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QSORT(3)		 BSD Library Functions Manual		      QSORT(3)

NAME
     qsort, heapsort, mergesort	-- sort	functions

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <stdlib.h>

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

     int
     heapsort(void *base, size_t nmemb,	size_t size,
	 int (*compar)(const void *, const void	*));

     int
     mergesort(void *base, size_t nmemb, size_t	size,
	 int (*compar)(const void *, const void	*));

DESCRIPTION
     The qsort() function is a modified	partition-exchange sort, or quicksort.
     The heapsort() function is	a modified selection sort.  The	mergesort()
     function is a modified merge sort with exponential	search intended	for
     sorting data with pre-existing order.

     The qsort() and heapsort()	functions sort an array	of nmemb objects, the
     initial member of which is	pointed	to by base.  The size of each object
     is	specified by size.  Mergesort()	behaves	similarly, but requires	that
     size be greater than "sizeof(void *) / 2".

     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.

     The functions qsort() and heapsort() are not stable, that is, if two mem-
     bers compare as equal, their order	in the sorted array is undefined.  The
     function mergesort() is stable.

     The qsort() function is an	implementation of C.A.R. Hoare's ``quicksort''
     algorithm,	a variant of partition-exchange	sorting; in particular,	see
     D.E. Knuth's Algorithm Q.	Qsort()	takes O	N lg N average time.  This im-
     plementation uses median selection	to avoid its O N**2 worst-case behav-
     ior.

     The heapsort() function is	an implementation of J.W.J. William's ``heap-
     sort'' algorithm, a variant of selection sorting; in particular, see D.E.
     Knuth's Algorithm H.  Heapsort() takes O N	lg N worst-case	time.  Its
     only advantage over qsort() is that it uses almost	no additional memory;
     while qsort() does	not allocate memory, it	is implemented using recur-
     sion.

     The function mergesort() requires additional memory of size nmemb * size
     bytes; it should be used only when	space is not at	a premium.
     Mergesort() is optimized for data with pre-existing order;	its worst case
     time is O N lg N; its best	case is	O N.

     Normally, qsort() is faster than mergesort() is faster than heapsort().
     Memory availability and pre-existing order	in the data can	make this un-
     true.

RETURN VALUES
     The qsort() function returns no value.

     The heapsort() and	mergesort() functions return the value 0 if success-
     ful; otherwise the	value -1 is returned and the global variable errno is
     set to indicate the error.

ERRORS
     The heapsort() and	mergesort() functions succeed unless:

     [EINVAL]		The size argument is zero, or, the size	argument to
			mergesort() is less than "sizeof(void *) / 2".

     [ENOMEM]		Heapsort() or mergesort() were unable to allocate mem-
			ory.

COMPATIBILITY
     Previous versions of qsort() did not permit the comparison	routine	itself
     to	call qsort(3).	This is	no longer true.

SEE ALSO
     sort(1), radixsort(3)

     Hoare, C.A.R., "Quicksort", The Computer Journal, 5:1, pp.	10-15, 1962.

     Williams, J.W.J, "Heapsort", Communications of the	ACM, 7:1, pp. 347-348,
     1964.

     Knuth, D.E., "Sorting and Searching", The Art of Computer Programming,
     Vol. 3, pp. 114-123, 145-149, 1968.

     Mcilroy, P.M., "Optimistic	Sorting	and Information	Theoretic Complexity",
     Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, January 1992.

     Bentley, J.L., "Engineering a Sort	Function", bentley@research.att.com,
     January 1992.

STANDARDS
     The qsort() function conforms to ISO/IEC 9899:1990	("ISO C90").

BSD				 June 4, 1993				   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | COMPATIBILITY | SEE ALSO | STANDARDS

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