bsearch---binary search
#include <stdlib.h>
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Descriptionbsearch searches an array beginning at base for any element
that matches key, using binary search. nmemb is the element
count of the array; size is the size of each element.
The array must be sorted in ascending order with respect to the
comparison function compar (which you supply as the last argument of
bsearch).
You must define the comparison function (*compar) to have two
arguments; its result must be negative if the first argument is
less than the second, zero if the two arguments match, and
positive if the first argument is greater than the second (where
"less than" and "greater than" refer to whatever arbitrary
ordering is appropriate).
Returns
Returns a pointer to an element of array that matches key. If
more than one matching element is available, the result may point to
any of them.
Portability
bsearch is ANSI.
No supporting OS subroutines are required.