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[/
Copyright 2010 Neil Groves
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
/]
[section:equal_range equal_range]
[heading Prototype]
``
template<
class ForwardRange,
class Value
>
std::pair<typename range_iterator<ForwardRange>::type,
typename range_iterator<ForwardRange>::type>
equal_range(ForwardRange& rng, const Value& val);
template<
class ForwardRange,
class Value
>
std::pair<typename range_iterator<const ForwardRange>::type,
typename range_iterator<const ForwardRange>::type>
equal_range(const ForwardRange& rng, const Value& val);
template<
class ForwardRange,
class Value,
class SortPredicate
>
std::pair<typename range_iterator<ForwardRange>::type,
typename range_iterator<ForwardRange>::type>
equal_range(ForwardRange& rng, const Value& val, SortPredicate pred);
template<
class ForwardRange,
class Value,
class SortPredicate
>
std::pair<typename range_iterator<const ForwardRange>::type,
typename range_iterator<const ForwardRange>::type>
equal_range(const ForwardRange& rng, const Value& val, SortPredicate pred);
``
[heading Description]
`equal_range` returns a range in the form of a pair of iterators where all of the elements are equal to `val`. If no values are found that are equal to `val`, then an empty range is returned, hence `result.first == result.second`. For the non-predicate versions of `equal_range` the equality of elements is determined by `operator<`.
For the predicate versions of `equal_range` the equality of elements is determined by `pred`.
[heading Definition]
Defined in the header file `boost/range/algorithm/equal_range.hpp`
[heading Requirements]
[*For the non-predicate versions:]
* `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:]
* `ForwardRange` is a model of the __forward_range__ Concept.
* `SortPredicate` is a model of the `StrictWeakOrderingConcept`.
* `ForwardRange`'s value type is the same as `Value`.
* `ForwardRange`'s value type is convertible to both of `SortPredicate`'s argument types.
[heading Precondition:]
For the non-predicate versions: `rng` is ordered in ascending order according to `operator<`.
For the predicate versions: `rng` is ordered in ascending order according to `pred`.
[heading Complexity]
For random-access ranges, the complexity is `O(log N)`, otherwise the complexity is `O(N)`.
[endsect]
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