NAME

std::transform_exclusive_scan - std::transform_exclusive_scan

Synopsis

Defined in header <numeric>
template< class InputIt, class OutputIt, class T,

class BinaryOperation, class UnaryOperation> (since C++17)
OutputIt transform_exclusive_scan( InputIt first, InputIt (until C++20)
last, OutputIt d_first, T init,

BinaryOperation binary_op, UnaryOperation unary_op );
template< class InputIt, class OutputIt, class T,

class BinaryOperation, class UnaryOperation>
constexpr OutputIt transform_exclusive_scan( InputIt first, (since C++20)
InputIt last, OutputIt d_first, (1)
T init, BinaryOperation binary_op,

UnaryOperation unary_op );
template< class ExecutionPolicy,

class ForwardIt1, class ForwardIt2,
class T, class BinaryOperation, class UnaryOperation >
ForwardIt2 transform_exclusive_scan( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first, T init,

BinaryOperation binary_op, UnaryOperation unary_op );

Transforms each element in the range [first, last) with unary_op, then computes an
exclusive prefix sum operation using binary_op over the resulting range, with init
as the initial value, and writes the results to the range beginning at d_first.
"exclusive" means that the i-th input element is not included in the i-th sum.

Formally, assigns through each iterator i in [d_first, d_first + (last - first)) the
value of the generalized noncommutative sum of init, unary_op(*j)... for every j in
[first, first + (i - d_first)) over binary_op,

where generalized noncommutative sum GNSUM(op, a
1, ..., a
N) is defined as follows:

* if N=1, a
1
* if N > 1, op(GNSUM(op, a
1, ..., a
K), GNSUM(op, a
M, ..., a
N)) for any K where 1 < K+1 = M ≤ N

In other words, the summation operations may be performed in arbitrary order, and
the behavior is nondeterministic if binary_op is not associative.

Overload (2) is executed according to policy. This overload does not participate in
overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) is true.

unary_op and binary_op shall not invalidate iterators (including the end iterators)
or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first +
(last - first)). Otherwise, the behavior is undefined.

Parameters

first, last - the range of elements to sum
d_first - the beginning of the destination range, may be equal to
first
policy - the execution policy to use. See execution policy for
details.
init - the initial value
unary FunctionObject that will be applied to each element
unary_op - of the input range. The return type must be acceptable as
input to binary_op.
binary FunctionObject that will be applied in to the
binary_op - result of unary_op, the results of other binary_op, and
init.

Type requirements

-
InputIt must meet the requirements of LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
T must meet the requirements of MoveConstructible. All of binary_op(init,
unary_op(*first)), binary_op(init, init), and binary_op(unary_op(*first),
unary_op(*first)) must be convertible to T.

Return value

Iterator to the element past the last element written.

Complexity

O(last - first) applications of each of binary_op and unary_op.

Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as
follows:

* If execution of a function invoked as part of the algorithm throws an exception
and ExecutionPolicy is one of the standard policies, std::terminate is called.
For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Notes

unary_op is not applied to init.

Example

// Run this code

#include <functional>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>

int main()
{
std::vector data {3, 1, 4, 1, 5, 9, 2, 6};

auto times_10 = [](int x) { return x * 10; };

std::cout << "10 times exclusive sum: ";
std::transform_exclusive_scan(data.begin(), data.end(),
std::ostream_iterator<int>(std::cout, " "),
0, std::plus<int>{}, times_10);
std::cout << "\n10 times inclusive sum: ";
std::transform_inclusive_scan(data.begin(), data.end(),
std::ostream_iterator<int>(std::cout, " "),
std::plus<int>{}, times_10);
}

Output:

10 times exclusive sum: 0 30 40 80 90 140 230 250
10 times inclusive sum: 30 40 80 90 140 230 250 310