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.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
bsearch() Thread safety MT-Safe


POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.


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

main(int argc, char *argv[])
    qsort(months, nr_of_months, sizeof(months[0]), compmi);
    for (int i = 1; i < argc; i++) {
        struct mi key;
        struct mi *res; = argv[i];
        res = bsearch(&key, months, nr_of_months,
                      sizeof(months[0]), 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 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at−pages/.

  Copyright 1993 David Metcalfe (

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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 (