std::exclusive_scan
| Defined in header <numeric>
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| template< class InputIt, class OutputIt, class T > OutputIt exclusive_scan( InputIt first, InputIt last, |
(1) | (since C++17) (constexpr since C++20) |
| template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > |
(2) | (since C++17) |
| template< class InputIt, class OutputIt, class T, class BinaryOp > |
(3) | (since C++17) (constexpr since C++20) |
| template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, |
(4) | (since C++17) |
[0, std::distance(first, last)), performs the following operations in order:
- Creates a sequence which is formed by init followed by the elements of
[first,iter)in order, where iter is the next ith iterator of first. - Computes the generalized noncommutative sum of the sequence over op.
- Assigns the result to *dest, where dest is the next ith iterator of d_first.
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std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
|
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
The generalized noncommutative sum of a sequence of elements over a binary operation binary_op is defined as follows:
- If the sequence only has one element, the sum is the value of the element.
- Otherwise, performs the following operations in order:
- Selects any two adjacent elements elem1 and elem2 from the sequence.
- Calculates binary_op(elem1, elem2) and replaces the two elements in the sequence with the result.
- Repeats steps 1 and 2 until there is only one element in the sequence.
Given binary_op as the actual binary operation:
- The result is non-deterministic if the binary_op is not associative (such as floating-point addition).
- If any of the following values is not convertible to
T, the program is ill-formed:
- binary_op(init, *first)
- binary_op(init, init)
- binary_op(*first, *first)
- If any of the following conditions is satisfied, the behavior is undefined:
-
Tis not MoveConstructible. - binary_op modifies any element of
[first,last). - binary_op invalidates any iterator or subrange of
[first,last].
-
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 |
| init | - | the initial value |
| op | - | binary FunctionObject that will be applied in to the result of dereferencing the input iterators, the results of other op, and init |
| Type requirements | ||
-InputIt must meet the requirements of LegacyInputIterator.
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-OutputIt must meet the requirements of LegacyOutputIterator.
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-ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.
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Return value
Iterator to the element past the last element written.
Complexity
Given N as std::distance(first, last):
Exceptions
The overloads with a template parameter named ExecutionPolicy report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Example
#include <functional> #include <iostream> #include <iterator> #include <numeric> #include <vector> int main() { std::vector data{3, 1, 4, 1, 5, 9, 2, 6}; std::cout << "Exclusive sum: "; std::exclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " "), 0); std::cout << "\nInclusive sum: "; std::inclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << "\n\nExclusive product: "; std::exclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " "), 1, std::multiplies<>{}); std::cout << "\nInclusive product: "; std::inclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " "), std::multiplies<>{}); }
Output:
Exclusive sum: 0 3 4 8 9 14 23 25 Inclusive sum: 3 4 8 9 14 23 25 31 Exclusive product: 1 3 3 12 12 60 540 1080 Inclusive product: 3 3 12 12 60 540 1080 6480
See also
| computes the differences between adjacent elements in a range (function template) | |
| sums up or folds a range of elements (function template) | |
| computes the partial sum of a range of elements (function template) | |
| (C++17) |
applies an invocable, then calculates exclusive scan (function template) |
| (C++17) |
similar to std::partial_sum, includes the ith input element in the ith sum (function template) |