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std::exclusive_scan(3) C++ Standard Libary std::exclusive_scan(3) NAME std::exclusive_scan - std::exclusive_scan Synopsis Defined in header <numeric> template< class InputIt, class OutputIt, class T > (since C++17) OutputIt exclusive_scan( InputIt first, InputIt last, (1) (const- expr since C++20) OutputIt d_first, T init ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, (2) (since C++17) ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init ); template< class InputIt, class OutputIt, class T, class BinaryOp > (since C++17) OutputIt exclusive_scan( InputIt first, InputIt last, (3) (const- expr since C++20) OutputIt d_first, T init, BinaryOp op ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOp > ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, (4) (since C++17) ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init, BinaryOp op ); 1) Equivalent to exclusive_scan(first, last, d_first, init, std::plus<>(). 3) Computes the exclusive prefix sum using op. For each integer i in [0, std::distance(first, last)), performs the following operations in order: 1. Creates a sequence which is formed by init followed by the ele- ments of [first, iter) in order, where iter is the next i th iterator of first. 2. Computes the generalized noncommutative sum of the sequence over op. 3. Assigns the result to *dest, where dest is the next i th iterator of d_first. 2,4) Same as (1,3), but executed according to policy. These overloads participate in overload resolution only if 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: 1. Selects any two adjacent elements elem1 and elem2 from the se- quence. 2. Calculates binary_op(elem1, elem2) and replaces the two elements in the sequence with the result. 3. Repeats steps 1 and 2 until there is only one element in the se- quence. Given binary_op as the actual binary operation: * The result is non-deterministic if the binary_op is not associa- tive (such as floating-point addition). * If any of the following values is not convertible to T, the pro- gram 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: * T is 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. See execution policy for details. 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. - OutputIt must meet the requirements of LegacyOutputIterator. - ForwardIt1, ForwardIt2 must meet the requirements of LegacyFor- wardIterator. Return value Iterator to the element past the last element written. Complexity Given \(\scriptsize N\)N as std::distance(first, last): 1,2) \(\scriptsize O(N)\)O(N) applications of std::plus<>(). 3,4) \(\scriptsize O(N)\)O(N) applications of op. 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 ExecutionPolicy is one of the standard policies, std::termi- nate is called. For any other ExecutionPolicy, the behavior is implementation- defined. * If the algorithm fails to allocate memory, std::bad_alloc is thrown. 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}; 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 adjacent_difference range (function template) accumulate sums up or folds a range of elements (function template) partial_sum computes the partial sum of a range of ele- ments (function template) transform_exclusive_scan applies an invocable, then calculates ex- clusive scan (C++17) (function template) inclusive_scan similar to std::partial_sum, includes the i^th input (C++17) element in the i^th sum (function template) http://cppreference.com 2024.06.10 std::exclusive_scan(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Example | Output: | See also
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