1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. 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 8.1 (Berkeley) 6/4/93 37.\" $FreeBSD$ 38.\" 39.Dd June 4, 1993 40.Dt QSORT 3 41.Os 42.Sh NAME 43.Nm qsort, heapsort, mergesort 44.Nd sort functions 45.Sh SYNOPSIS 46.Fd #include <stdlib.h> 47.Ft void 48.Fn qsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)" 49.Ft int 50.Fn heapsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)" 51.Ft int 52.Fn mergesort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)" 53.Sh DESCRIPTION 54The 55.Fn qsort 56function is a modified partition-exchange sort, or quicksort. 57The 58.Fn heapsort 59function is a modified selection sort. 60The 61.Fn mergesort 62function is a modified merge sort with exponential search 63intended for sorting data with pre-existing order. 64.Pp 65The 66.Fn qsort 67and 68.Fn heapsort 69functions sort an array of 70.Fa nmemb 71objects, the initial member of which is pointed to by 72.Fa base . 73The size of each object is specified by 74.Fa size . 75.Fn Mergesort 76behaves similarly, but 77.Em requires 78that 79.Fa size 80be greater than 81.Dq "sizeof(void *) / 2" . 82.Pp 83The contents of the array 84.Fa base 85are sorted in ascending order according to 86a comparison function pointed to by 87.Fa compar , 88which requires two arguments pointing to the objects being 89compared. 90.Pp 91The comparison function must return an integer less than, equal to, or 92greater than zero if the first argument is considered to be respectively 93less than, equal to, or greater than the second. 94.Pp 95The functions 96.Fn qsort 97and 98.Fn heapsort 99are 100.Em not 101stable, that is, if two members compare as equal, their order in 102the sorted array is undefined. 103The function 104.Fn mergesort 105is stable. 106.Pp 107The 108.Fn qsort 109function is an implementation of C.A.R. Hoare's ``quicksort'' algorithm, 110a variant of partition-exchange sorting; in particular, see D.E. Knuth's 111Algorithm Q. 112.Fn Qsort 113takes O N lg N average time. 114This implementation uses median selection to avoid its 115O N**2 worst-case behavior. 116.Pp 117The 118.Fn heapsort 119function is an implementation of J.W.J. William's ``heapsort'' algorithm, 120a variant of selection sorting; in particular, see D.E. Knuth's Algorithm H. 121.Fn Heapsort 122takes O N lg N worst-case time. 123Its 124.Em only 125advantage over 126.Fn qsort 127is that it uses almost no additional memory; while 128.Fn qsort 129does not allocate memory, it is implemented using recursion. 130.Pp 131The function 132.Fn mergesort 133requires additional memory of size 134.Fa nmemb * 135.Fa size 136bytes; it should be used only when space is not at a premium. 137.Fn Mergesort 138is optimized for data with pre-existing order; its worst case 139time is O N lg N; its best case is O N. 140.Pp 141Normally, 142.Fn qsort 143is faster than 144.Fn mergesort 145is faster than 146.Fn heapsort . 147Memory availability and pre-existing order in the data can make this 148untrue. 149.Sh RETURN VALUES 150The 151.Fn qsort 152function 153returns no value. 154.Pp 155Upon successful completion, 156.Fn heapsort 157and 158.Fn mergesort 159return 0. 160Otherwise, they return \-1 and the global variable 161.Va errno 162is set to indicate the error. 163.Sh ERRORS 164The 165.Fn heapsort 166and 167.Fn mergesort 168functions succeed unless: 169.Bl -tag -width Er 170.It Bq Er EINVAL 171The 172.Fa size 173argument is zero, or, 174the 175.Fa size 176argument to 177.Fn mergesort 178is less than 179.Dq "sizeof(void *) / 2" . 180.It Bq Er ENOMEM 181.Fn Heapsort 182or 183.Fn mergesort 184were unable to allocate memory. 185.El 186.Sh COMPATIBILITY 187Previous versions of 188.Fn qsort 189did not permit the comparison routine itself to call 190.Fn qsort 3 . 191This is no longer true. 192.Sh SEE ALSO 193.Xr sort 1 , 194.Xr radixsort 3 195.Rs 196.%A Hoare, C.A.R. 197.%D 1962 198.%T "Quicksort" 199.%J "The Computer Journal" 200.%V 5:1 201.%P pp. 10-15 202.Re 203.Rs 204.%A Williams, J.W.J 205.%D 1964 206.%T "Heapsort" 207.%J "Communications of the ACM" 208.%V 7:1 209.%P pp. 347-348 210.Re 211.Rs 212.%A Knuth, D.E. 213.%D 1968 214.%B "The Art of Computer Programming" 215.%V Vol. 3 216.%T "Sorting and Searching" 217.%P pp. 114-123, 145-149 218.Re 219.Rs 220.%A Mcilroy, P.M. 221.%T "Optimistic Sorting and Information Theoretic Complexity" 222.%J "Fourth Annual ACM-SIAM Symposium on Discrete Algorithms" 223.%V January 1992 224.Re 225.Rs 226.%A Bentley, J.L. 227.%T "Engineering a Sort Function" 228.%J "bentley@research.att.com" 229.%V January 1992 230.Re 231.Sh STANDARDS 232The 233.Fn qsort 234function 235conforms to 236.St -ansiC . 237