discard_iterator#

class discard_iterator#

discard_iterator is an iterator which represents a special kind of pointer that ignores values written to it upon dereference.

This iterator is useful for ignoring the output of certain algorithms without wasting memory capacity or bandwidth. discard_iterator may also be used to count the size of an algorithm’s output which may not be known a priori.

The following code snippet demonstrates how to use discard_iterator to ignore one of the output ranges of reduce_by_key

#include <cuda/iterator>
#include <thrust/reduce.h>
#include <thrust/device_vector.h>

int main()
{
  thrust::device_vector<int> keys{1, 3, 3, 3, 2, 2, 1};
  thrust::device_vector<int> values{9, 8, 7, 6, 5, 4, 3};

  thrust::device_vector<int> result(4);

  // we are only interested in the reduced values
  // use discard_iterator to ignore the output keys
  thrust::reduce_by_key(keys.begin(), keys.end(),
                        values.begin(),
                        cuda::discard_iterator{},
                        result.begin());

  // result is now [9, 21, 9, 3]

  return 0;
}

Public Types

using iterator_concept = ::cuda::std::random_access_iterator_tag#
using iterator_category = ::cuda::std::random_access_iterator_tag#
using difference_type = ::cuda::std::ptrdiff_t#
using value_type = void#
using pointer = void#
using reference = void#

Public Functions

constexpr discard_iterator() = default#

Default constructs a discard_iterator at index zero.

template<class _Integer, ::cuda::std::enable_if_t<::cuda::std::__integer_like<_Integer>, int> = 0>
inline constexpr discard_iterator(
_Integer __index,
) noexcept#

Constructs a discard_iterator with a given index.

Parameters:

__index – The index used for the discard iterator

inline constexpr difference_type index() const noexcept#

Returns the stored index.

inline constexpr __discard_proxy operator*() const noexcept#

Dereferences the discard_iterator returning a proxy that discards all values that are assigned to it.

inline constexpr __discard_proxy operator[](
difference_type,
) const noexcept#

Subscipts the discard_iterator returning a proxy that discards all values that are assigned to it.

inline constexpr discard_iterator &operator++() noexcept#

Increments the stored index.

inline constexpr discard_iterator operator++(int) noexcept#

Increments the stored index.

inline constexpr discard_iterator &operator--() noexcept#

Decrements the stored index.

inline constexpr discard_iterator operator--(int) noexcept#

Decrements the stored index.

inline constexpr discard_iterator operator+(
difference_type __n,
) const noexcept#

Returns a copy of this discard_iterator advanced by a number of elements.

Parameters:

__n – The number of elements to advance

inline constexpr discard_iterator &operator+=(
difference_type __n,
) noexcept#

Advances the index of this discard_iterator by a number of elements.

Parameters:

__n – The number of elements to advance

inline constexpr discard_iterator operator-(
difference_type __n,
) const noexcept#

Returns a copy of this discard_iterator decremented by a number of elements.

Parameters:

__n – The number of elements to decrement

inline constexpr discard_iterator &operator-=(
difference_type __n,
) noexcept#

Decrements the index of the discard_iterator by a number of elements.

Parameters:

__n – The number of elements to decrement

Friends

inline friend constexpr discard_iterator operator+(
difference_type __n,
const discard_iterator &__x,
) noexcept#

Returns a copy of a discard_iterator advanced by a number of elements.

Parameters:

  • __n – The number of elements to advance

  • __x – The original discard_iterator

inline friend constexpr difference_type operator-(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Returns the distance between two discard_iterator's.

Parameters:
Returns:

__rhs.__index_ - __lhs.__index_

inline friend constexpr difference_type operator-(
const discard_iterator &__lhs,
::cuda::std::default_sentinel_t,
) noexcept#

Returns the distance between a default_sentinel and a discard_iterator.

Parameters:

__lhs – The discard_iterator

Returns:

-__lhs.__index_

inline friend constexpr difference_type operator-(
::cuda::std::default_sentinel_t,
const discard_iterator &__rhs,
) noexcept#

Returns the distance between a discard_iterator and a default_sentinel.

Parameters:

__rhs – The discard_iterator

Returns:

__rhs.__index_

inline friend constexpr bool operator==(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Compares two discard_iterator for equality by comparing the indices.

inline friend constexpr bool operator==(
const discard_iterator &__lhs,
::cuda::std::default_sentinel_t,
) noexcept#

Compares a discard_iterator with default_sentinel.

Parameters:

__lhs – is zero

Returns:

True if the index of

inline friend constexpr bool operator<(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Compares two discard_iterator for less than by comparing the indices.

inline friend constexpr bool operator<=(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Compares two discard_iterator for less equal by comparing the indices.

inline friend constexpr bool operator>(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Compares two discard_iterator for greater than by comparing the indices.

inline friend constexpr bool operator>=(
const discard_iterator &__lhs,
const discard_iterator &__rhs,
) noexcept#

Compares two discard_iterator for greater equal by comparing the indices.

template<class _Integer = ::cuda::std::ptrdiff_t, ::cuda::std::enable_if_t<::cuda::std::__integer_like<_Integer>, int> = 0>
inline constexpr discard_iterator make_discard_iterator(
_Integer __index = 0,
)#

Creates a discard_iterator from an optional index.

Parameters:

__index – The index of the discard_iterator within a range. The default index is 0.

Returns:

A new discard_iterator with __index as the counter.