[section:binary_search binary_search]

[heading Prototype]

``
template<class ForwardRange, class Value>
bool binary_search(const ForwardRange& rng, const Value& val);

template<class ForwardRange, class Value, class BinaryPredicate>
bool binary_search(const ForwardRange& rng, const Value& val, BinaryPredicate pred);
``

[heading Description]

`binary_search` returns `true` if and only if the value `val` exists in the range `rng`.

[heading Definition]

Defined in the header file `boost/range/algorithm/binary_search.hpp`

[heading Requirements]

[*For the non-predicate versions of binary_search:]

* `ForwardRange` is a model of the __forward_range__ Concept.
* `Value` is a model of the `LessThanComparableConcept`.
* The ordering of objects of type `Value` is a [*/strict weak ordering/], as defined in the `LessThanComparableConcept` requirements.
* `ForwardRange`'s value type is the same type as `Value`.

[*For the predicate versions of binary_search:]

* `ForwardRange` is a model of the __forward_range__ Concept.
* `BinaryPredicate` is a model of the `StrictWeakOrderingConcept`.
* `ForwardRange`'s value type is the same type as `Value`.
* `ForwardRange`'s value type is convertible to `BinaryPredicate`'s argument type.

[heading Precondition:]

[*For the non-predicate version:]

`rng` is ordered in ascending order according to `operator<`.

[*For the predicate version:]

`rng` is ordered in ascending order according to the function object `pred`.

[heading Complexity]

For non-random-access ranges, the complexity is `O(N)` where `N` is `distance(rng)`.

For random-access ranges, the complexity is `O(log N)` where `N` is `distance(rng)`.

[endsect]