bsearch(3)



BSEARCH(3)                 Linux Programmer's Manual                BSEARCH(3)

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,  respec-
       tively, 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 |
       +----------+---------------+---------+

CONFORMING TO
       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);
       }

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

COLOPHON
       This  page  is  part of release 4.12 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/.

                                  2015-08-08                        BSEARCH(3)

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