bsearch(3) — Linux manual page

bsearch(3)              Library Functions Manual              bsearch(3)

NAME

       bsearch - binary search of a sorted array

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #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]));

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 │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C89, C99, SVr4, 4.3BSD.

EXAMPLES

       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);
       }

SEE ALSO

       hsearch(3), lsearch(3), qsort(3), tsearch(3)

COLOPHON

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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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