std::transform_exclusive_scan - cppreference.com (original) (raw)

Defined in header
template< class InputIt, class OutputIt, class T, class BinaryOp, class UnaryOp >OutputIt transform_exclusive_scan ( InputIt first, InputIt last, OutputIt d_first, T init, BinaryOp binary_op, UnaryOp unary_op );	(1)	(since C++17) (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOp, class UnaryOp >ForwardIt2 transform_exclusive_scan ( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init, BinaryOp binary_op, UnaryOp unary_op );	(2)	(since C++17)

For each integer i in [0, std::distance(first, last)), performs the following operations in order:

Creates a sequence which is formed by init followed by the values transformed from the elements of [first, iter) in order by unary_op, where iter is the next ith iterator of first.
Computes the generalized noncommutative sum of the sequence over binary_op.
Assigns the result to *dest, where dest is the next ith iterator of d_first.

This overload participates in overload resolution only if all following conditions are satisfied:

The generalized noncommutative sum of a sequence of elements over a binary operation binary_op is defined as follows:

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.

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:

If any of the following conditions is satisfied, the behavior is undefined:

T is not MoveConstructible.
unary_op or binary_op modifies any element of [first, last).
unary_op or binary_op invalidates any iterator or subrange of [first, last].

first, last	-	the pair of iterators defining 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
unary_op	-	unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op.
binary_op	-	binary FunctionObject that will be applied in to the 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.

Iterator to the element past the last element written.

Given \(\scriptsize N\)N as std::distance(first, last):

1,2) \(\scriptsize O(N)\)O(N) applications of unary_op and binary_op respectively.

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.

unary_op is never applied to init.

#include #include #include #include #include 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(std::cout, " "), 0, std::plus{}, times_10); std::cout << "\n10 times inclusive sum: "; std::transform_inclusive_scan(data.begin(), data.end(), std::ostream_iterator(std::cout, " "), std::plus{}, times_10); std::cout << '\n'; }

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

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