170 lines
4.7 KiB
Groff
170 lines
4.7 KiB
Groff
.\" Copyright (c) 1990, 1991 The Regents of the University of California.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to Berkeley by
|
|
.\" the American National Standards Committee X3, on Information
|
|
.\" Processing Systems.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the University of
|
|
.\" California, Berkeley and its contributors.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" from: @(#)qsort.3 6.7 (Berkeley) 6/29/91
|
|
.\" $Id: qsort.3,v 1.2 1993/08/01 07:44:22 mycroft Exp $
|
|
.\"
|
|
.Dd June 29, 1991
|
|
.Dt QSORT 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm qsort, heapsort
|
|
.Nd sort functions
|
|
.Sh SYNOPSIS
|
|
.Fd #include <stdlib.h>
|
|
.Ft void
|
|
.Fn qsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)"
|
|
.Ft int
|
|
.Fn heapsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn qsort
|
|
function is a modified partition-exchange sort, or quicksort.
|
|
The
|
|
.Fn heapsort
|
|
function is a modified selection sort.
|
|
.Pp
|
|
The
|
|
.Fn qsort
|
|
and
|
|
.Fn heapsort
|
|
functions sort an array of
|
|
.Fa nmemb
|
|
objects, the initial member of which is pointed to by
|
|
.Fa base .
|
|
The size of each object is specified by
|
|
.Fa size .
|
|
.Pp
|
|
The contents of the array are sorted in ascending order according to
|
|
a comparison function pointed to by
|
|
.Fa compar ,
|
|
which is called with two arguments that point to the objects being
|
|
compared.
|
|
.Pp
|
|
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.
|
|
.Pp
|
|
The functions
|
|
.Fn qsort
|
|
and
|
|
.Fn heapsort
|
|
are
|
|
.Em not
|
|
stable, that is, if two members compare as equal, their order in
|
|
the sorted array is undefined.
|
|
.Pp
|
|
The
|
|
.Fn 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.
|
|
.Fn Qsort
|
|
takes O N lg N average time.
|
|
This implementation uses median selection to avoid the traditional
|
|
O N**2 worst-case behavior.
|
|
.Pp
|
|
The
|
|
.Fn heapsort
|
|
function is an implementation of J.W.J. William's ``heapsort'' algorithm,
|
|
a variant of selection sorting; in particular, see D.E. Knuth's Algorithm H.
|
|
.Fn Heapsort
|
|
takes O N lg N worst-case time.
|
|
Its
|
|
.Em only
|
|
advantage over
|
|
.Fn qsort
|
|
is that it uses no additional memory.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn qsort
|
|
function
|
|
returns no value.
|
|
.Pp
|
|
Upon successful completion,
|
|
.Fn heapsort
|
|
returns 0.
|
|
Otherwise, it returns \-1 and the global variable
|
|
.Va errno
|
|
is set to indicate the error.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn heapsort
|
|
function succeeds unless:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa size
|
|
argument is zero.
|
|
.Sh COMPATIBILITY
|
|
Previous versions of
|
|
.Fn qsort
|
|
did not permit the comparison routine to itself call
|
|
.Fn qsort 3 .
|
|
This is no longer true.
|
|
.Sh SEE ALSO
|
|
.Xr sort 1 ,
|
|
.Xr radixsort 3
|
|
.Rs
|
|
.%A Hoare, C.A.R.
|
|
.%D 1962
|
|
.%T "Quicksort"
|
|
.%J "The Computer Journal"
|
|
.%V 5:1
|
|
.%P pp. 10-15
|
|
.Re
|
|
.Rs
|
|
.%A Williams, J.W.J
|
|
.%D 1964
|
|
.%T "Heapsort"
|
|
.%J "Communications of the ACM"
|
|
.%V 7:1
|
|
.%P pp. 347-348
|
|
.Re
|
|
.Rs
|
|
.%A Knuth, D.E.
|
|
.%D 1968
|
|
.%B "The Art of Computer Programming"
|
|
.%V Vol. 3
|
|
.%T "Sorting and Searching"
|
|
.%P pp. 114-123, 145-149
|
|
.Re
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn qsort
|
|
function
|
|
conforms to
|
|
.St -ansiC .
|