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

1. Computes the inclusive 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 the values transformed from the elements of [first, iter] in order by unary_op, where iter is the next ith iterator of first.
2. Computes the generalized noncommutative sum of the sequence over binary_op.
3. Assigns the result to *dest, where dest is the next ith iterator of d_first.

1. Same as (1), but each sequence created is formed by init followed by the elements of [first, iter] in order.

2,4) Same as (1,3), but executed according to policy.

These overloads participate 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:

• 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 sequence.
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 sequence.

The result is non-deterministic if the binary_op is not associative (such as floating-point addition).

For overloads (1,2), if binary_op(unary_op(*first), unary_op(*first)) is not convertible to the value type of decltype(first), the program is ill-formed.

For overloads (3,4), if any of the following values is not convertible to T, the program is ill-formed:

• binary_op(init, init)
• binary_op(init, unary_op(*first))
• binary_op(unary_op(*first), unary_op(*first))

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

• For overloads (1,2), the value type of decltype(first) is not MoveConstructible.
• For overloads (3,4), 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].

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Notes
• 6 Example
• 7 See also

[edit] Parameters

[edit] Return value

Iterator to the element past the last element written.

[edit] Complexity

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

1-4) \(\scriptsize O(N)\)O(N) applications of unary_op and binary_op respectively.

[edit] 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::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Notes

unary_op is never applied to init.

The parameter init appears last, differing from std::transform_exclusive_scan, because it is optional for this function.

[edit] Example

#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

[edit] See also