BSEARCH(3)             FreeBSD Library Functions Manual             BSEARCH(3)

NAME
     bsearch - binary search of a sorted table

LIBRARY
     Standard C Library (libc, -lc)

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, respectively,
     to be less than, to match, or be greater than the array member.  See the
     int_compare sample function in qsort(3) for a comparison function that is
     also compatible with bsearch().

RETURN VALUES
     The bsearch() function returns a pointer to a matching member of the
     array, or a null pointer if no match is found.  If two members compare as
     equal, which member is matched is unspecified.

EXAMPLES
     A sample program that searches people by age in a sorted array:

     #include <assert.h>
     #include <stdint.h>
     #include <stdio.h>
     #include <stdlib.h>
     #include <string.h>

     struct person {
             const char      *name;
             int             age;
     };

     static int
     compare(const void *a, const void *b)
     {
             const int *age;
             const struct person *person;

             age = a;
             person = b;

             return (*age - person->age);
     }

     int
     main(void)
     {
             struct person *friend;
             int age;
             /* Sorted array */
             const struct person friends[] = {
                     { "paul", 22 },
                     { "anne", 25 },
                     { "fred", 25 },
                     { "mary", 27 },
                     { "mark", 35 },
                     { "bill", 50 }
             };
             const size_t len = sizeof(friends) / sizeof(friends[0]);

             age = 22;
             friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
             assert(strcmp(friend->name, "paul") == 0);
             printf("name: %s\nage: %d\n", friend->name, friend->age);

             age = 25;
             friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);

             /*
              * For multiple elements with the same key, it is implementation
              * defined which will be returned
              */
             assert(strcmp(friend->name, "fred") == 0 ||
                 strcmp(friend->name, "anne") == 0);
             printf("name: %s\nage: %d\n", friend->name, friend->age);

             age = 30;
             friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
             assert(friend == NULL);
             printf("friend aged 30 not found\n");
     }

SEE ALSO
     db(3), lsearch(3), qsort(3)

STANDARDS
     The bsearch() function conforms to ISO/IEC 9899:1990 ("ISO C90").

FreeBSD 13.1-RELEASE-p6          July 17, 2019         FreeBSD 13.1-RELEASE-p6