[unix-history] / lib / libc / stdlib / qsort.3

.\" 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.
.\"
.\"     @(#)qsort.3	6.7 (Berkeley) 6/29/91
.\"
.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 .
Commit	Line	Data
15637ed4 RG	1	.\" Copyright (c) 1990, 1991 The Regents of the University of California.
	2	.\" All rights reserved.
	3	.\"
	4	.\" This code is derived from software contributed to Berkeley by
	5	.\" the American National Standards Committee X3, on Information
	6	.\" Processing Systems.
	7	.\"
	8	.\" Redistribution and use in source and binary forms, with or without
	9	.\" modification, are permitted provided that the following conditions
	10	.\" are met:
	11	.\" 1. Redistributions of source code must retain the above copyright
	12	.\" notice, this list of conditions and the following disclaimer.
	13	.\" 2. Redistributions in binary form must reproduce the above copyright
	14	.\" notice, this list of conditions and the following disclaimer in the
	15	.\" documentation and/or other materials provided with the distribution.
	16	.\" 3. All advertising materials mentioning features or use of this software
	17	.\" must display the following acknowledgement:
	18	.\" This product includes software developed by the University of
	19	.\" California, Berkeley and its contributors.
	20	.\" 4. Neither the name of the University nor the names of its contributors
	21	.\" may be used to endorse or promote products derived from this software
	22	.\" without specific prior written permission.
	23	.\"
	24	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	25	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	26	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	27	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	28	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	29	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	30	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	31	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	32	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	33	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	34	.\" SUCH DAMAGE.
	35	.\"
	36	.\" @(#)qsort.3 6.7 (Berkeley) 6/29/91
	37	.\"
	38	.Dd June 29, 1991
	39	.Dt QSORT 3
	40	.Os
	41	.Sh NAME
	42	.Nm qsort, heapsort
	43	.Nd sort functions
	44	.Sh SYNOPSIS
	45	.Fd #include <stdlib.h>
	46	.Ft void
	47	.Fn qsort "void base" "size_t nmemb" "size_t size" "int (compar)(const void , const void )"
	48	.Ft int
	49	.Fn heapsort "void base" "size_t nmemb" "size_t size" "int (compar)(const void , const void )"
	50	.Sh DESCRIPTION
	51	The
	52	.Fn qsort
	53	function is a modified partition-exchange sort, or quicksort.
	54	The
	55	.Fn heapsort
	56	function is a modified selection sort.
	57	.Pp
	58	The
	59	.Fn qsort
	60	and
	61	.Fn heapsort
	62	functions sort an array of
	63	.Fa nmemb
	64	objects, the initial member of which is pointed to by
65	.Fa base .
66	The size of each object is specified by
67	.Fa size .
68	.Pp
69	The contents of the array are sorted in ascending order according to
70	a comparison function pointed to by
71	.Fa compar ,
72	which is called with two arguments that point to the objects being
73	compared.
74	.Pp
75	The comparison function must return an integer less than, equal to, or
76	greater than zero if the first argument is considered to be respectively
77	less than, equal to, or greater than the second.
78	.Pp
79	The functions
80	.Fn qsort
81	and
82	.Fn heapsort
83	are
84	.Em not
85	stable, that is, if two members compare as equal, their order in
86	the sorted array is undefined.
87	.Pp
88	The
89	.Fn qsort
90	function is an implementation of C.A.R. Hoare's ``quicksort'' algorithm,
91	a variant of partition-exchange sorting; in particular, see D.E. Knuth's
92	Algorithm Q.
93	.Fn Qsort
94	takes O N lg N average time.
95	This implementation uses median selection to avoid the traditional
96	O N**2 worst-case behavior.
97	.Pp
98	The
99	.Fn heapsort
100	function is an implementation of J.W.J. William's ``heapsort'' algorithm,
101	a variant of selection sorting; in particular, see D.E. Knuth's Algorithm H.
102	.Fn Heapsort
103	takes O N lg N worst-case time.
104	Its
105	.Em only
106	advantage over
107	.Fn qsort
108	is that it uses no additional memory.
109	.Sh RETURN VALUES
110	The
111	.Fn qsort
112	function
113	returns no value.
114	.Pp
115	Upon successful completion,
116	.Fn heapsort
117	returns 0.
118	Otherwise, it returns \-1 and the global variable
119	.Va errno
120	is set to indicate the error.
121	.Sh ERRORS
122	The
123	.Fn heapsort
124	function succeeds unless:
125	.Bl -tag -width Er
126	.It Bq Er EINVAL
127	The
128	.Fa size
129	argument is zero.
130	.Sh COMPATIBILITY
131	Previous versions of
132	.Fn qsort
133	did not permit the comparison routine to itself call
134	.Fn qsort 3 .
135	This is no longer true.
136	.Sh SEE ALSO
137	.Xr sort 1 ,
138	.Xr radixsort 3
139	.Rs
140	.%A Hoare, C.A.R.
141	.%D 1962
142	.%T "Quicksort"
143	.%J "The Computer Journal"
144	.%V 5:1
145	.%P pp. 10-15
146	.Re
147	.Rs
148	.%A Williams, J.W.J
149	.%D 1964
150	.%T "Heapsort"
151	.%J "Communications of the ACM"
152	.%V 7:1
153	.%P pp. 347-348
154	.Re
155	.Rs
156	.%A Knuth, D.E.
157	.%D 1968
158	.%B "The Art of Computer Programming"
159	.%V Vol. 3
160	.%T "Sorting and Searching"
161	.%P pp. 114-123, 145-149
162	.Re
163	.Sh STANDARDS
164	The
165	.Fn qsort
166	function
167	conforms to
168	.St -ansiC .