NAME
bsearch, bsearch_b, bsearch_s – binary search of a sorted table
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
QVoid *
bsearch(const void *key, QVoid *base, size_t nmemb, size_t size, int (*compar) (const void *, const void *));
QVoid *
bsearch_b(const void *key, QVoid *base, size_t nmemb, size_t size, int (^compar) (const void *, const void *));
#define __STDC_WANT_LIB_EXT1__ 1
QVoid *
bsearch_s(const void *key, QVoid *base, rsize_t nmemb, rsize_t size, int (*compar) (const void *, const void *, void *), void *context);
DESCRIPTION
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. See the int_compare sample function in qsort(3) for a comparison function that is also compatible with bsearch().
The bsearch_b() function behaves identically to bsearch(), except the callback compar takes a block pointer instead of a function pointer.
The bsearch_s() function behaves identically to bsearch(), except the callback compar is called with a third argument, context, which is passed through from the caller. Runtime-constraint violation occurs if:
-
nmemb or size is greater than RSIZE_MAX
-
nmemb is not zero and any of key, base, or compar is a null pointer
On a runtime-constraint violation, the runtime-constraint handler is invoked, bsearch_s() does not search the array, and a null pointer is returned. Note that the handler is called before bsearch_s() returns, and the handler function might not return. If nmemb is zero, the comparison function is not called, no match is found, and key, base, and compar may be null pointers.
RETURN VALUES
The bsearch(), bsearch_b(), and bsearch_s() functions return a pointer to a matching member of the array, or a null pointer if no match is found. bsearch_s() also returns a null pointer if there is a runtime-constraint violation. If two members compare as equal, which member is matched is unspecified.
EXAMPLES
A sample program that searches people by age in a sorted array:
#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\nage: %d\n", 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\nage: %d\n", friend->name, friend->age);
age = 30;
friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
assert(friend == NULL);
printf("friend aged 30 not found\n");
}
SEE ALSO
STANDARDS
The bsearch() function conforms to ISO/IEC 9899:2024 (“ISO C23”), where it is specified as a qualifier-preserving function.
The bsearch_s() function conforms to ISO/IEC 9899:2024 (“ISO C23”), section K.3.6.3.2. Like bsearch(), it is specified as a qualifier-preserving function.
HISTORY
The bsearch(), initially specified in the -svid1, first appeared in AT&T System V Release 2 UNIX and later in 4.3BSD. It was first standardized in ISO/IEC 9899:1990 (“ISO C90”).
The bsearch_b() function first appeared in Mac OS X and was later added to FreeBSD 11.0 as an extension.
The bsearch_s() function first appeared in FreeBSD 16.0. It was first standardized in ISO/IEC 9899:2011 (“ISO C11”).