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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); }