ceph/src/boost/libs/range/doc/reference/algorithm/count_if.qbk

   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