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BSEARCH(3)		     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 mem-
     ber  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  ex-
     pected  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 compati-
     ble 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 ports 15.1		  July 17, 2019 		      BSEARCH(3)

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