bsearch
NAME
bsearch - binary search of a sorted array
SYNOPSIS
#include <stdlib.h> I void *bsearch(const void * key , const void * base , size_t nmemb ,I size_t size , int (* compar )(const void *, const void *));
DESCRIPTION
The
R 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
R 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.
CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001, C89, C99
EXAMPLE
The example below first sorts an array of structures using
qsort(3),
then retrieves desired elements using
R 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);
}
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