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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.
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);
}
This page is part of release 3.52 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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Copyright 1993 David Metcalfe (davidprism.demon.co.uk) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END 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 (faithcs.unc.edu) |