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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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bsearch(3) Library Functions Manual bsearch(3)
bsearch - binary search of a sorted array
Standard C library (libc, -lc)
#include <stdlib.h>
void *bsearch(const void key[.size], const void base[.size * .nmemb],
size_t nmemb, size_t size,
int (*compar)(const void [.size], const void [.size]));
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.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ bsearch() │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
POSIX.1-2001, C89, C99, SVr4, 4.3BSD.
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>
#define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))
struct mi {
int nr;
const char *name;
};
static struct mi 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" }
};
static int
compmi(const void *m1, const void *m2)
{
const struct mi *mi1 = m1;
const struct mi *mi2 = m2;
return strcmp(mi1->name, mi2->name);
}
int
main(int argc, char *argv[])
{
qsort(months, ARRAY_SIZE(months), sizeof(months[0]), compmi);
for (size_t i = 1; i < argc; i++) {
struct mi key;
struct mi *res;
key.name = argv[i];
res = bsearch(&key, months, ARRAY_SIZE(months),
sizeof(months[0]), compmi);
if (res == NULL)
printf("'%s': unknown month\n", argv[i]);
else
printf("%s: month #%d\n", res->name, res->nr);
}
exit(EXIT_SUCCESS);
}
hsearch(3), lsearch(3), qsort(3), tsearch(3)
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Linux man-pages 6.9.1 2024-06-15 bsearch(3)
Pages that refer to this page: hsearch(3), lsearch(3), qsort(3), tsearch(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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