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.\" @(#)bsearch.3 8.3 (Berkeley) 4/19/94 33.\" $FreeBSD$ 34.\" 35.Dd July 17, 2019 36.Dt BSEARCH 3 37.Os 38.Sh NAME 39.Nm bsearch 40.Nd binary search of a sorted table 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In stdlib.h 45.Ft void * 46.Fn bsearch "const void *key" "const void *base" "size_t nmemb" "size_t size" "int (*compar) (const void *, const void *)" 47.Sh DESCRIPTION 48The 49.Fn bsearch 50function searches an array of 51.Fa nmemb 52objects, the initial member of which is 53pointed to by 54.Fa base , 55for a member that matches the object pointed to by 56.Fa key . 57The size of each member of the array is specified by 58.Fa size . 59.Pp 60The contents of the array should be in ascending sorted order according 61to the comparison function referenced by 62.Fa compar . 63The 64.Fa compar 65routine 66is expected to have 67two arguments which point to the 68.Fa key 69object and to an array member, in that order, and should return an integer 70less than, equal to, or greater than zero if the 71.Fa key 72object is found, respectively, to be less than, to match, or be 73greater than the array member. 74See the 75.Fa int_compare 76sample function in 77.Xr qsort 3 78for a comparison function that is also compatible with 79.Fn bsearch . 80.Sh RETURN VALUES 81The 82.Fn bsearch 83function returns a pointer to a matching member of the array, or a null 84pointer if no match is found. 85If two members compare as equal, which member is matched is unspecified. 86.Sh EXAMPLES 87A sample program that searches people by age in a sorted array: 88.Bd -literal 89#include <assert.h> 90#include <stdint.h> 91#include <stdio.h> 92#include <stdlib.h> 93#include <string.h> 94 95struct person { 96 const char *name; 97 int age; 98}; 99 100static int 101compare(const void *a, const void *b) 102{ 103 const int *age; 104 const struct person *person; 105 106 age = a; 107 person = b; 108 109 return (*age - person->age); 110} 111 112int 113main(void) 114{ 115 struct person *friend; 116 int age; 117 /* Sorted array */ 118 const struct person friends[] = { 119 { "paul", 22 }, 120 { "anne", 25 }, 121 { "fred", 25 }, 122 { "mary", 27 }, 123 { "mark", 35 }, 124 { "bill", 50 } 125 }; 126 const size_t len = sizeof(friends) / sizeof(friends[0]); 127 128 age = 22; 129 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 130 assert(strcmp(friend->name, "paul") == 0); 131 printf("name: %s\enage: %d\en", friend->name, friend->age); 132 133 age = 25; 134 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 135 136 /* 137 * For multiple elements with the same key, it is implementation 138 * defined which will be returned 139 */ 140 assert(strcmp(friend->name, "fred") == 0 || 141 strcmp(friend->name, "anne") == 0); 142 printf("name: %s\enage: %d\en", friend->name, friend->age); 143 144 age = 30; 145 friend = bsearch(&age, friends, len, sizeof(friends[0]), compare); 146 assert(friend == NULL); 147 printf("friend aged 30 not found\en"); 148} 149.Ed 150.Sh SEE ALSO 151.Xr db 3 , 152.Xr lsearch 3 , 153.Xr qsort 3 154.\" .Xr tsearch 3 155.Sh STANDARDS 156The 157.Fn bsearch 158function conforms to 159.St -isoC . 160