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