| Brian Silverman | 598d029 | 2018-08-04 23:56:47 -0700 | [diff] [blame^] | 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 | `` |
| 11 | template<class SinglePassRange, class UnaryPredicate> |
| 12 | typename range_difference<const SinglePassRange>::type |
| 13 | count_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 | |
| 22 | Defined 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 | |
| 33 | Linear. Exactly `distance(rng)` invocations of `pred`. |
| 34 | |
| 35 | [endsect] |
| 36 | |
| 37 | |