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count_if
Description

Returns the number of elements within a sequence with a type for which a given unary function object evaluates to true.

Synopsis
template<
    typename Sequence,
    typename F
    >
typename result_of::count_if<Sequence, F>::type count_if(
    Sequence const& seq, F f);

Table 1.56. Parameters

Parameter

Requirement

Description

seq

A model of Forward Sequence, f(e) is a valid expression, convertible to bool, for each element e in seq

The sequence to search

f

A unary function object

The search predicate


Expression Semantics
count_if(seq, f)

Return type: int

Semantics: Returns the number of elements in seq where f evaluates to true.

Complexity

Linear. At most result_of::size<Sequence>::value comparisons.

Header
#include <boost/fusion/algorithm/query/count_if.hpp>
#include <boost/fusion/include/count_if.hpp>
Example
const vector<int,int,int> vec(1,2,3);
assert(count_if(vec,odd()) == 2);

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