The number of comparisons will be logarithmic (and as few as possible). The number of steps through the sequence will be logarithmic for random-access iterators (e.g., pointers), and linear otherwise.
The LWG has passed Defect Report 270, which notes: The proposed resolution reinterprets binary search. Instead of thinking about searching for a value in a sorted range, we view that as an important special case of a more general algorithm: searching for the partition point in a partitioned range. We also add a guarantee that the old wording did not: we ensure that the upper bound is no earlier than the lower bound, that the pair returned by equal_range is a valid range, and that the first part of that pair is the lower bound.
The actual effect of the first sentence is that a comparison functor passed by the user doesn't necessarily need to induce a strict weak ordering relation. Rather, it partitions the range.
bool std::binary_search | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val, | |||
_Compare | __comp | |||
) |
Determines whether an element exists in a range.
first | An iterator. | |
last | Another iterator. | |
val | The search term. | |
comp | A functor to use for comparisons. |
The comparison function should have the same effects on ordering as the function used for the initial sort.
Definition at line 4260 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned_pred, and std::lower_bound().
bool std::binary_search | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val | |||
) |
Determines whether an element exists in a range.
first | An iterator. | |
last | Another iterator. | |
val | The search term. |
Definition at line 4228 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned, and std::lower_bound().
pair<_ForwardIterator, _ForwardIterator> std::equal_range | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val, | |||
_Compare | __comp | |||
) |
Finds the largest subrange in which val could be inserted at any place in it without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. | |
comp | A functor to use for comparisons. |
std::make_pair(lower_bound(first, last, val, comp), upper_bound(first, last, val, comp))
Definition at line 4170 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned_pred, std::advance(), std::distance(), std::lower_bound(), and std::upper_bound().
Referenced by std::__debug::set< _Key, _Compare, _Allocator >::equal_range(), std::__debug::multiset< _Key, _Compare, _Allocator >::equal_range(), std::__debug::multimap< _Key, _Tp, _Compare, _Allocator >::equal_range(), std::__debug::map< _Key, _Tp, _Compare, _Allocator >::equal_range(), __gnu_cxx::__debug::hash_set< _Value, _HashFcn, _EqualKey, _Alloc >::equal_range(), __gnu_cxx::__debug::hash_multiset< _Value, _HashFcn, _EqualKey, _Alloc >::equal_range(), __gnu_cxx::__debug::hash_multimap< _Value, _Tp, _HashFcn, _EqualKey, _Alloc >::equal_range(), and __gnu_cxx::__debug::hash_map< _Value, _Tp, _HashFcn, _EqualKey, _Alloc >::equal_range().
pair<_ForwardIterator, _ForwardIterator> std::equal_range | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val | |||
) |
Finds the largest subrange in which val could be inserted at any place in it without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. |
std::make_pair(lower_bound(first, last, val), upper_bound(first, last, val))
Definition at line 4109 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned, std::advance(), std::distance(), std::lower_bound(), and std::upper_bound().
_ForwardIterator std::lower_bound | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val, | |||
_Compare | __comp | |||
) |
Finds the first position in which val could be inserted without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. | |
comp | A functor to use for comparisons. |
Definition at line 2934 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned_pred, std::advance(), and std::distance().
Referenced by std::map< _Key, _Tp, _Compare, _Allocator >::at(), and std::map< _Key, _Tp, _Compare, _Allocator >::operator[]().
_ForwardIterator std::lower_bound | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val | |||
) |
Finds the first position in which val could be inserted without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. |
Definition at line 2884 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned, std::advance(), and std::distance().
Referenced by std::__merge_adaptive(), std::__merge_without_buffer(), __gnu_cxx::__stl_next_prime(), std::tr1::__detail::_Prime_rehash_policy::_M_bkt_for_elements(), std::tr1::__detail::_Prime_rehash_policy::_M_need_rehash(), std::tr1::__detail::_Prime_rehash_policy::_M_next_bkt(), std::binary_search(), and std::equal_range().
_ForwardIterator std::upper_bound | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val, | |||
_Compare | __comp | |||
) |
Finds the last position in which val could be inserted without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. | |
comp | A functor to use for comparisons. |
Definition at line 3031 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned_pred, std::advance(), and std::distance().
_ForwardIterator std::upper_bound | ( | _ForwardIterator | __first, | |
_ForwardIterator | __last, | |||
const _Tp & | __val | |||
) |
Finds the last position in which val could be inserted without changing the ordering.
first | An iterator. | |
last | Another iterator. | |
val | The search term. |
Definition at line 2981 of file stl_algo.h.
References __glibcxx_function_requires, __glibcxx_requires_partitioned, std::advance(), and std::distance().
Referenced by std::__merge_adaptive(), std::__merge_without_buffer(), and std::equal_range().