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template<class SinglePassRange, class UnaryPredicate> typename range_difference<const SinglePassRange>::type count_if(const SinglePassRange& rng, UnaryPredicate pred);
count_if returns the
number of elements x
in rng where pred(x)
is true.
Defined in the header file boost/range/algorithm/count_if.hpp
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.
SinglePassRange
is convertible to the argument type of UnaryPredicate.
Linear. Exactly distance(rng) invocations of pred.