Function template count

Function template count_if

hpx::parallel::v1::count_if

Synopsis

// In header: <hpx/parallel/detail/count.hpp>


template<typename ExPolicy, typename InIter, typename F> 
  unspecified count_if(ExPolicy && policy, InIter first, InIter last, F && f);

Description

Returns the number of elements in the range [first, last) satisfying a specific criteria. This version counts elements for which predicate f returns true.

	Note
	Complexity: Performs exactly last - first applications of the predicate.

Note

The assignments in the parallel count_if algorithm invoked with an execution policy object of type sequential_execution_policy execute in sequential order in the calling thread.

The assignments in the parallel count_if algorithm invoked with an execution policy object of type parallel_execution_policy or task_execution_policy are permitted to execute in an unordered fashion in unspecified threads, and indeterminately sequenced within each thread.

Parameters:

`f`	Specifies the function (or function object) which will be invoked for each of the elements in the sequence specified by [first, last).This is an unary predicate which returns true for the required elements. The signature of this predicate should be equivalent to: bool pred(const Type &a); The signature does not need to have const&, but the function must not modify the objects passed to it. The type Type must be such that an object of type InIter can be dereferenced and then implicitly converted to Type.
`first`	Refers to the beginning of the sequence of elements the algorithm will be applied to.
`last`	Refers to the end of the sequence of elements the algorithm will be applied to.
`policy`	The execution policy to use for the scheduling of the iterations.

Template Parameters:

`ExPolicy`	The type of the execution policy to use (deduced). It describes the manner in which the execution of the algorithm may be parallelized and the manner in which it executes the comparisons.
`F`	The type of the function/function object to use (deduced). Unlike its sequential form, the parallel overload of count_if requires F to meet the requirements of CopyConstructible.
`InIter`	The type of the source iterators used (deduced). This iterator type must meet the requirements of an input iterator.

Returns:

The count_if algorithm returns hpx::future<difference_type> if the execution policy is of type task_execution_policy and returns difference_type otherwise (where difference_type is defined by std::iterator_traits<InIter>::difference_type. The count algorithm returns the number of elements satisfying the given criteria.