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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 (until C++20) last, OutputIt d_first, T init ); template< class InputIt, class OutputIt, class T > constexpr OutputIt exclusive_scan( InputIt (since C++20) first, InputIt last, OutputIt d_first, T init ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > ForwardIt2 exclusive_scan( ExecutionPolicy&& (2) (since C++17) policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init ); template< class InputIt, class OutputIt, (1) class T, class BinaryOperation > OutputIt exclusive_scan( InputIt first, InputIt (since C++17) last, (until C++20) OutputIt d_first, T init, BinaryOperation binary_op ); template< class InputIt, class OutputIt, class T, class BinaryOperation > constexpr OutputIt exclusive_scan( InputIt (since C++20) first, InputIt last, (3) OutputIt d_first, T init, BinaryOperation binary_op ); template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOperation > ForwardIt2 exclusive_scan( ExecutionPolicy&& (4) (since C++17) policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init, BinaryOperation binary_op ); Computes an exclusive prefix sum operation using binary_op (or std::plus<>() for overloads (1-2)) for the range [first, last), using init as the ini- tial 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, *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 arbi- trary order, and the behavior is nondeterministic if binary_op is not associative. Overloads (2,4) are executed according to policy. These overloads do 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. binary_op shall not invalidate iterators (including the end itera- tors) 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 binary FunctionObject that will be applied in to the result of binary_op - dereferencing the input iterators, 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 LegacyFor- wardIterator. - T must meet the requirements of MoveConstructible. and bi- nary_op(init, *first), binary_op(init, init), and binary_op(*first, *first) must be con- vertible to T Return value Iterator to the element past the last element written. Complexity O(last - first) applications of the binary operation 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 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 ith input element (C++17) in the ith sum (function template) http://cppreference.com 2022.07.31 std::exclusive_scan(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Complexity | Exceptions | Example | Output: | See also
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