xref: /freebsd/lib/libc/stdlib/bsearch.3 (revision 345e740a1bd30cd8511dfc0957dc0eaef4353d5c)

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.\"     @(#)bsearch.3	8.3 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd July 17, 2019
.Dt BSEARCH 3
.Os
.Sh NAME
.Nm bsearch
.Nd binary search of a sorted table
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft void *
.Fn bsearch "const void *key" "const void *base" "size_t nmemb" "size_t size" "int (*compar) (const void *, const void *)"
.Sh DESCRIPTION
The
.Fn bsearch
function searches an array of
.Fa nmemb
objects, the initial member of which is
pointed to by
.Fa base ,
for a member that matches the object pointed to by
.Fa key .
The size of each member of the array is specified by
.Fa size .
.Pp
The contents of the array should be in ascending sorted order according
to the comparison function referenced by
.Fa compar .
The
.Fa compar
routine
is expected to have
two arguments which point to the
.Fa 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
.Fa key
object is found, respectively, to be less than, to match, or be
greater than the array member.
See the
.Fa int_compare
sample function in
.Xr qsort 3
for a comparison function that is also compatible with
.Fn bsearch .
.Sh RETURN VALUES
The
.Fn bsearch
function returns a pointer to a matching member of the array, or a null
pointer if no match is found.
If two members compare as equal, which member is matched is unspecified.
.Sh EXAMPLES
A sample program that searches people by age in a sorted array:
.Bd -literal
#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct person {
	const char 	*name;
	int 		age;
};

static int
compare(const void *a, const void *b)
{
	const int *age;
	const struct person *person;

	age = a;
	person = b;

	return (*age - person->age);
}

int
main(void)
{
	struct person *friend;
	int age;
	/* Sorted array */
	const struct person friends[] = {
		{ "paul", 22 },
		{ "anne", 25 },
		{ "fred", 25 },
		{ "mary", 27 },
		{ "mark", 35 },
		{ "bill", 50 }
	};
	const size_t len = sizeof(friends) / sizeof(friends[0]);

	age = 22;
	friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
	assert(strcmp(friend->name, "paul") == 0);
	printf("name: %s\enage: %d\en", friend->name, friend->age);

	age = 25;
	friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);

	/*
	 * For multiple elements with the same key, it is implementation
	 * defined which will be returned
	 */
	assert(strcmp(friend->name, "fred") == 0 ||
	    strcmp(friend->name, "anne") == 0);
	printf("name: %s\enage: %d\en", friend->name, friend->age);

	age = 30;
	friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
	assert(friend == NULL);
	printf("friend aged 30 not found\en");
}
.Ed
.Sh SEE ALSO
.Xr db 3 ,
.Xr lsearch 3 ,
.Xr qsort 3
.\" .Xr tsearch 3
.Sh STANDARDS
The
.Fn bsearch
function conforms to
.St -isoC .