QSORT(3)                    BSD Programmer's Manual                   QSORT(3)

NAME
     qsort, heapsort - sort functions

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 *))

DESCRIPTION
     The qsort() function is a modified partition-exchange sort, or quicksort.
     The heapsort() function is a modified selection sort.

     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.

     The contents of the array are sorted in ascending order according to a
     comparison function pointed to by compar, which is called with two argu-
     ments 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.

     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 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 the traditional O N**2 worst-
     case behavior.

     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 no additional memory.

RETURN VALUES
     The qsort() function returns no value.

     Upon successful completion, heapsort() returns 0.  Otherwise, it returns
     -1 and the global variable errno is set to indicate the error.

ERRORS
     The heapsort() function succeeds unless:

     [EINVAL]      The size argument is zero.

COMPATIBILITY
     Previous versions of qsort() did not permit the comparison routine to it-
     self 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.

STANDARDS
     The qsort() function conforms to ANSI C3.159-1989 (``ANSI C'').

BSDI BSD/386                    March 26, 1993                               2