NAME¶
bsearch - binary search of a sorted array
SYNOPSIS¶
#include <stdlib.h>
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
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.
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).
| Interface |
Attribute |
Value |
| bsearch () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
EXAMPLE¶
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);
}
int
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;
key.name = argv[i];
res = bsearch(&key, months, nr_of_months,
sizeof(struct mi), compmi);
if (res == NULL)
printf("'%s': unknown month\n", argv[i]);
else
printf("%s: month #%d\n", res->name, res->nr);
}
exit(EXIT_SUCCESS);
}
COLOPHON¶
This page is part of release 5.04 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 https://www.kernel.org/doc/man-pages/.
