1.\" 2.\" The contents of this file are subject to the terms of the 3.\" Common Development and Distribution License (the "License"). 4.\" You may not use this file except in compliance with the License. 5.\" 6.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 7.\" or http://www.opensolaris.org/os/licensing. 8.\" See the License for the specific language governing permissions 9.\" and limitations under the License. 10.\" 11.\" When distributing Covered Code, include this CDDL HEADER in each 12.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. 13.\" If applicable, add the following below this CDDL HEADER, with the 14.\" fields enclosed by brackets "[]" replaced with your own identifying 15.\" information: Portions Copyright [yyyy] [name of copyright owner] 16.\" 17.\" 18.\" Copyright 1989 AT&T 19.\" Copyright (c) 2002, Sun Microsystems, Inc. All Rights Reserved 20.\" Copyright 2020 Oxide Computer Company 21.\" 22.Dd October 11, 2020 23.Dt QSORT 3C 24.Os 25.Sh NAME 26.Nm qsort , 27.Nm qsort_r 28.Nd quick sort 29.Sh SYNOPSIS 30.In stdlib.h 31.Ft void 32.Fo qsort 33.Fa "void *base" 34.Fa "size_t nel" 35.Fa "size_t width" 36.Fa "int (*compar)(const void *, const void *)" 37.Fc 38.Ft void 39.Fo qsort_r 40.Fa "void *base" 41.Fa "size_t nel" 42.Fa "size_t width" 43.Fa "int (*compar_arg)(const void *, const void *, void *)" 44.Fa "void *arg" 45.Fc 46.Sh DESCRIPTION 47The 48.Fn qsort 49function is an implementation of the quick-sort algorithm. 50It sorts a table of data in place. 51The contents of the table are sorted in ascending order according to the 52user-supplied comparison function. 53.Pp 54The 55.Fa Ibase 56argument points to the element at the base of the table. 57The 58.Fa nel 59argument is the number of elements in the table. 60The 61.Fa width 62argument specifies the size of each element in bytes. 63The 64.Fa compar 65arguments that point to the elements being compared. 66The comparison function need not compare every byte, so arbitrary data may be 67contained in the elements in addition to the values being compared. 68.Pp 69The function must return an integer less than, equal to, or greater than zero 70to indicate if the first argument is to be considered less than, equal to, or 71greater than the second argument. 72.Pp 73The contents of the table are sorted in ascending order according to the user 74supplied comparison function. 75The relative order in the output of two items that compare as equal is 76unpredictable. 77.Pp 78The 79.Fn qsort_r 80function behaves similarly to the 81.Fn qsort 82function, except that its comparison function, 83.Fn compar_arg , 84takes an extra argument which is the 85.Fn qsort_r 86argument 87.Fa arg . 88This allows one to avoid global data in the comparison function, unlike 89with the 90.Fn qsort 91function. 92.Pp 93The 94.Fn qsort 95and 96.Fn qsort_r 97function safely allows concurrent access by multiple threads 98to disjoint data, such as overlapping subtrees or tables. 99.Sh EXAMPLES 100.Sy Example 1 101Program sorts. 102.Pp 103The following program sorts a simple array: 104.Bd -literal 105#include <stdlib.h> 106#include <stdio.h> 107 108static int 109intcompare(const void *p1, const void *p2) 110{ 111 int i = *((int *)p1); 112 int j = *((int *)p2); 113 114 if (i > j) 115 return (1); 116 if (i < j) 117 return (-1); 118 return (0); 119} 120 121int 122main() 123{ 124 int i; 125 int a[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 }; 126 size_t nelems = sizeof (a) / sizeof (int); 127 128 qsort((void *)a, nelems, sizeof (int), intcompare); 129 130 for (i = 0; i < nelems; i++) { 131 (void) printf("%d ", a[i]); 132 } 133 134 (void) printf("\en"); 135 return (0); 136} 137.Ed 138.Sh INTERFACE STABILITY 139.Sy Standard 140.Sh MT-LEVEL 141.Sy MT-Safe 142.Sh SEE ALSO 143.Xr sort 1 , 144.Xr bsearch 3C , 145.Xr lsearch 3C , 146.Xr string 3C , 147.Xr attributes 5 , 148.Xr standards 5 149