---
name: "bsearch"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/bsearch"
---

# bsearch(3)

binary search of a sorted array

## NAME

bsearch - binary search of a sorted array

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdlib.h>
```

**void \*bsearch(**size\_t n, size\_t size;               **const void** *key***\[***size***\], const void** *base***\[***size* **\*** *n***\],**               **size\_t** *n***, size\_t** *size***,**               **typeof(int (const void \[***size***\], const void \[***size***\]))**                   **\****compar***);**

## DESCRIPTION

The **bsearch**() function searches an array of *n* 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.

## RETURN VALUE

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.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **bsearch**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

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

## EXAMPLES

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

```
#include <stdcountof.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct mi {
    int         nr;
    const char  *name;
};
static struct mi  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" }
};
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);
}
int
main(int argc, char *argv[])
{
    qsort(months, countof(months), sizeof(months[0]), compmi);
    for (size_t i = 1; i < argc; i++) {
        struct mi key;
        struct mi *res;
        key.name = argv[i];
        res = bsearch(&key, months, countof(months),
                      sizeof(months[0]), compmi);
        if (res == NULL)
            printf("'%s': unknown month\n", argv[i]);
        else
            printf("%s: month #%d\n", res->name, res->nr);
    }
    exit(EXIT_SUCCESS);
}
```

## SEE ALSO

[**hsearch**(3)](/hsearch/3.md), [**lsearch**(3)](/lsearch/3.md), [**qsort**(3)](/qsort/3.md), [**tsearch**(3)](/tsearch/3.md)