1[/ 2 Copyright 2010 Neil Groves 3 Distributed under the Boost Software License, Version 1.0. 4 (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 5/] 6[section:count_if count_if] 7 8[heading Prototype] 9 10`` 11template<class SinglePassRange, class UnaryPredicate> 12typename range_difference<const SinglePassRange>::type 13count_if(const SinglePassRange& rng, UnaryPredicate pred); 14`` 15 16[heading Description] 17 18`count_if` returns the number of elements `x` in `rng` where `pred(x)` is `true`. 19 20[heading Definition] 21 22Defined in the header file `boost/range/algorithm/count_if.hpp` 23 24[heading Requirements] 25 26* `SinglePassRange` is a model of the __single_pass_range__ Concept. 27* `UnaryPredicate` is a model of the `UnaryPredicateConcept`. 28* `SinglePassRange`'s value type is a model of the `EqualityComparableConcept`. 29* The value type of `SinglePassRange` is convertible to the argument type of `UnaryPredicate`. 30 31[heading Complexity] 32 33Linear. Exactly `distance(rng)` invocations of `pred`. 34 35[endsect] 36 37 38