bsearch - binary search of a sorted array.
key, const void base, size_t nmemb,
size_t size, int (compar)(const void *, const void *));
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.
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.
SVID 3, BSD 4.3, ISO 9899