287 lines
6.6 KiB
Groff
287 lines
6.6 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
|
|
.\" 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.
|
|
.\" 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.
|
|
.\"
|
|
.\" @(#)qsort.3 8.1 (Berkeley) 6/4/93
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd September 30, 2003
|
|
.Dt QSORT 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm qsort , qsort_r , heapsort , mergesort
|
|
.Nd sort functions
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In stdlib.h
|
|
.Ft void
|
|
.Fo qsort
|
|
.Fa "void *base"
|
|
.Fa "size_t nmemb"
|
|
.Fa "size_t size"
|
|
.Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
|
|
.Fc
|
|
.Ft void
|
|
.Fo qsort_r
|
|
.Fa "void *base"
|
|
.Fa "size_t nmemb"
|
|
.Fa "size_t size"
|
|
.Fa "void *thunk"
|
|
.Fa "int \*[lp]*compar\*[rp]\*[lp]void *, const void *, const void *\*[rp]"
|
|
.Fc
|
|
.Ft int
|
|
.Fo heapsort
|
|
.Fa "void *base"
|
|
.Fa "size_t nmemb"
|
|
.Fa "size_t size"
|
|
.Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
|
|
.Fc
|
|
.Ft int
|
|
.Fo mergesort
|
|
.Fa "void *base"
|
|
.Fa "size_t nmemb"
|
|
.Fa "size_t size"
|
|
.Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]"
|
|
.Fc
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn qsort
|
|
function is a modified partition-exchange sort, or quicksort.
|
|
The
|
|
.Fn heapsort
|
|
function is a modified selection sort.
|
|
The
|
|
.Fn mergesort
|
|
function is a modified merge sort with exponential search
|
|
intended for sorting data with pre-existing order.
|
|
.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 .
|
|
The
|
|
.Fn mergesort
|
|
function
|
|
behaves similarly, but
|
|
.Em requires
|
|
that
|
|
.Fa size
|
|
be greater than
|
|
.Dq "sizeof(void *) / 2" .
|
|
.Pp
|
|
The contents of the array
|
|
.Fa base
|
|
are sorted in ascending order according to
|
|
a comparison function pointed to by
|
|
.Fa compar ,
|
|
which requires two arguments pointing 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
|
|
.Fn qsort_r
|
|
function behaves identically to
|
|
.Fn qsort ,
|
|
except that it takes an additional argument,
|
|
.Fa thunk ,
|
|
which is passed unchanged as the first argument to function pointed to
|
|
.Fa compar .
|
|
This allows the comparison function to access additional
|
|
data without using global variables, and thus
|
|
.Fn qsort_r
|
|
is suitable for use in functions which must be reentrant.
|
|
.Pp
|
|
The algorithms implemented by
|
|
.Fn qsort ,
|
|
.Fn qsort_r ,
|
|
and
|
|
.Fn heapsort
|
|
are
|
|
.Em not
|
|
stable, that is, if two members compare as equal, their order in
|
|
the sorted array is undefined.
|
|
The
|
|
.Fn mergesort
|
|
algorithm is stable.
|
|
.Pp
|
|
The
|
|
.Fn qsort
|
|
and
|
|
.Fn qsort_r
|
|
functions are an implementation of C.A.R.
|
|
Hoare's
|
|
.Dq quicksort
|
|
algorithm,
|
|
a variant of partition-exchange sorting; in particular, see
|
|
.An D.E. Knuth Ns 's
|
|
.%T "Algorithm Q" .
|
|
.Sy Quicksort
|
|
takes O N lg N average time.
|
|
This implementation uses median selection to avoid its
|
|
O N**2 worst-case behavior.
|
|
.Pp
|
|
The
|
|
.Fn heapsort
|
|
function is an implementation of
|
|
.An "J.W.J. William" Ns 's
|
|
.Dq heapsort
|
|
algorithm,
|
|
a variant of selection sorting; in particular, see
|
|
.An "D.E. Knuth" Ns 's
|
|
.%T "Algorithm H" .
|
|
.Sy Heapsort
|
|
takes O N lg N worst-case time.
|
|
Its
|
|
.Em only
|
|
advantage over
|
|
.Fn qsort
|
|
is that it uses almost no additional memory; while
|
|
.Fn qsort
|
|
does not allocate memory, it is implemented using recursion.
|
|
.Pp
|
|
The function
|
|
.Fn mergesort
|
|
requires additional memory of size
|
|
.Fa nmemb *
|
|
.Fa size
|
|
bytes; it should be used only when space is not at a premium.
|
|
The
|
|
.Fn mergesort
|
|
function
|
|
is optimized for data with pre-existing order; its worst case
|
|
time is O N lg N; its best case is O N.
|
|
.Pp
|
|
Normally,
|
|
.Fn qsort
|
|
is faster than
|
|
.Fn mergesort
|
|
is faster than
|
|
.Fn heapsort .
|
|
Memory availability and pre-existing order in the data can make this
|
|
untrue.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn qsort
|
|
and
|
|
.Fn qsort_r
|
|
functions
|
|
return no value.
|
|
.Pp
|
|
.Rv -std heapsort mergesort
|
|
.Sh COMPATIBILITY
|
|
Previous versions of
|
|
.Fn qsort
|
|
did not permit the comparison routine itself to call
|
|
.Fn qsort 3 .
|
|
This is no longer true.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn heapsort
|
|
and
|
|
.Fn mergesort
|
|
functions succeed unless:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa size
|
|
argument is zero, or,
|
|
the
|
|
.Fa size
|
|
argument to
|
|
.Fn mergesort
|
|
is less than
|
|
.Dq "sizeof(void *) / 2" .
|
|
.It Bq Er ENOMEM
|
|
The
|
|
.Fn heapsort
|
|
or
|
|
.Fn mergesort
|
|
functions
|
|
were unable to allocate memory.
|
|
.El
|
|
.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
|
|
.Rs
|
|
.%A McIlroy, P.M.
|
|
.%T "Optimistic Sorting and Information Theoretic Complexity"
|
|
.%J "Fourth Annual ACM-SIAM Symposium on Discrete Algorithms"
|
|
.%V January 1992
|
|
.Re
|
|
.Rs
|
|
.%A Bentley, J.L.
|
|
.%A McIlroy, M.D.
|
|
.%T "Engineering a Sort Function"
|
|
.%J "Software--Practice and Experience"
|
|
.%V Vol. 23(11)
|
|
.%P pp. 1249-1265
|
|
.%D November\ 1993
|
|
.Re
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn qsort
|
|
function
|
|
conforms to
|
|
.St -isoC .
|