| [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] |
| |
| |
