libs/range/doc/reference/algorithm/count_if.qbk
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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)
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[section:count_if count_if]
[heading Prototype]
``
template<class SinglePassRange, class UnaryPredicate>
typename range_difference<const SinglePassRange>::type
count_if(const SinglePassRange& rng, UnaryPredicate pred);
``
[heading Description]
`count_if` returns the number of elements `x` in `rng` where `pred(x)` is `true`.
[heading Definition]
Defined in the header file `boost/range/algorithm/count_if.hpp`
[heading Requirements]
* `SinglePassRange` is a model of the __single_pass_range__ Concept.
* `UnaryPredicate` is a model of the `UnaryPredicateConcept`.
* `SinglePassRange`'s value type is a model of the `EqualityComparableConcept`.
* The value type of `SinglePassRange` is convertible to the argument type of `UnaryPredicate`.
[heading Complexity]
Linear. Exactly `distance(rng)` invocations of `pred`.
[endsect]
