1.\" Copyright (c) 1990, 1991, 1993, 1994 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. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.Dd July 17, 2019 33.Dt BSEARCH 3 34.Os 35.Sh NAME 36.Nm bsearch 37.Nd binary search of a sorted table 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdlib.h 42.Ft void * 43.Fn bsearch "const void *key" "const void *base" "size_t nmemb" "size_t size" "int (*compar) (const void *, const void *)" 44.Sh DESCRIPTION 45The 46.Fn bsearch 47function searches an array of 48.Fa nmemb 49objects, the initial member of which is 50pointed to by 51.Fa base , 52for a member that matches the object pointed to by 53.Fa key . 54The size of each member of the array is specified by 55.Fa size . 56.Pp 57The contents of the array should be in ascending sorted order according 58to the comparison function referenced by 59.Fa compar . 60The 61.Fa compar 62routine 63is expected to have 64two arguments which point to the 65.Fa key 66object and to an array member, in that order, and should return an integer 67less than, equal to, or greater than zero if the 68.Fa key 69object is found, respectively, to be less than, to match, or be 70greater than the array member. 71See the 72.Fa int_compare 73sample function in 74.Xr qsort 3 75for a comparison function that is also compatible with 76.Fn bsearch . 77.Sh RETURN VALUES 78The 79.Fn bsearch 80function returns a pointer to a matching member of the array, or a null 81pointer if no match is found. 82If two members compare as equal, which member is matched is unspecified. 83.Sh EXAMPLES 84A sample program that searches people by age in a sorted array: 85.Bd -literal 86#include <assert.h> 87#include <stdint.h> 88#include <stdio.h> 89#include <stdlib.h> 90#include <string.h> 91 92struct person { 93 const char *name; 94 int age; 95}; 96 97static int 98compare(const void *a, const void *b) 99{ 100 const int *age; 101 const struct person *person; 102 103 age = a; 104 person = b; 105 106 return (*age - person->age); 107} 108 109int 110main(void) 111{ 112 struct person *friend; 113 int age; 114 /* Sorted array */ 115 const struct person friends[] = { 116 { "paul", 22 }, 117 { "anne", 25 }, 118 { "fred", 25 }, 119 { "mary", 27 }, 120 { "mark", 35 }, 121 { "bill", 50 } 122 }; 123 const size_t len = sizeof(friends) / sizeof(friends[0]); 124 125 age = 22; 126 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 127 assert(strcmp(friend->name, "paul") == 0); 128 printf("name: %s\enage: %d\en", friend->name, friend->age); 129 130 age = 25; 131 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 132 133 /* 134 * For multiple elements with the same key, it is implementation 135 * defined which will be returned 136 */ 137 assert(strcmp(friend->name, "fred") == 0 || 138 strcmp(friend->name, "anne") == 0); 139 printf("name: %s\enage: %d\en", friend->name, friend->age); 140 141 age = 30; 142 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 143 assert(friend == NULL); 144 printf("friend aged 30 not found\en"); 145} 146.Ed 147.Sh SEE ALSO 148.Xr db 3 , 149.Xr lsearch 3 , 150.Xr qsort 3 151.\" .Xr tsearch 3 152.Sh STANDARDS 153The 154.Fn bsearch 155function conforms to 156.St -isoC . 157