bsearch — binary search of a sorted array


#include <stdlib.h>
void *bsearch( const void *key,
  const void *base,
  size_t nmemb,
  size_t size,
  int (*compar)(const void *, const void *));


The bsearch() function searches an array of nmemb objects, the initial member of which is pointed to by base, for a member that matches the object pointed to by key. The size of each member of the array is specified by size.

The contents of the array should be in ascending sorted order according to the comparison function referenced by compar. The compar routine is expected to have two arguments which point to the key object and to an array member, in that order, and should return an integer less than, equal to, or greater than zero if the key object is found, respectively, to be less than, to match, or be greater than the array member.


The bsearch() function returns a pointer to a matching member of the array, or NULL if no match is found. If there are multiple elements that match the key, the element returned is unspecified.


SVr4, 4.3BSD, POSIX.1-2001, C89, C99.


The example below first sorts an array of structures using qsort(3), then retrieves desired elements using bsearch().

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct mi {
    int nr;
    char *name;
} months[] = {
    { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
    { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
    { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }

#define nr_of_months (sizeof(months)/sizeof(months[0]))

static int
compmi(const void *m1, const void *m2)
    struct mi *mi1 = (struct mi *) m1;
    struct mi *mi2 = (struct mi *) m2;
    return strcmp(mi1−>name, mi2−>name);

main(int argc, char **argv)
    int i;

    qsort(months, nr_of_months, sizeof(struct mi), compmi);
    for (i = 1; i < argc; i++) {
        struct mi key, *res; = argv[i];
        res = bsearch(&key, months, nr_of_months,
                      sizeof(struct mi), compmi);
        if (res == NULL)
            printf("'%s': unknown month\n", argv[i]);
            printf("%s: month #%d\n", res−>name, res−>nr);


hsearch(3), lsearch(3), qsort(3), tsearch(3)


This page is part of release 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at−pages/.

  Copyright 1993 David Metcalfe (

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages
Modified Mon Mar 29 22:41:16 1993, David Metcalfe
Modified Sat Jul 24 21:35:16 1993, Rik Faith (