[exclusive.scan]

# 26 Algorithms library [[algorithms]](./#algorithms)

## 26.10 Generalized numeric operations [[numeric.ops]](numeric.ops#exclusive.scan)

### 26.10.8 Exclusive scan [exclusive.scan]

[🔗](#lib:exclusive_scan)

`template<class InputIterator, class OutputIterator, class T>
  constexpr OutputIterator
    exclusive_scan(InputIterator first, InputIterator last,
                   OutputIterator result, T init);
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12710)

*Effects*: Equivalent to:return exclusive_scan(first, last, result, init, plus<>());

[🔗](#lib:exclusive_scan_)

`template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T>
  ForwardIterator2
    exclusive_scan(ExecutionPolicy&& exec,
                   ForwardIterator1 first, ForwardIterator1 last,
                   ForwardIterator2 result, T init);
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12728)

*Effects*: Equivalent to:return exclusive_scan(std::forward<ExecutionPolicy>(exec),
 first, last, result, init, plus<>());

[🔗](#lib:exclusive_scan__)

`template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
  constexpr OutputIterator
    exclusive_scan(InputIterator first, InputIterator last,
                   OutputIterator result, T init, BinaryOperation binary_op);
template<class ExecutionPolicy,
         class ForwardIterator1, class ForwardIterator2, class T, class BinaryOperation>
  ForwardIterator2
    exclusive_scan(ExecutionPolicy&& exec,
                   ForwardIterator1 first, ForwardIterator1 last,
                   ForwardIterator2 result, T init, BinaryOperation binary_op);
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12752)

*Mandates*: All of 

- [(3.1)](#3.1)

binary_op(init, init),

- [(3.2)](#3.2)

binary_op(init, *first), and

- [(3.3)](#3.3)

binary_op(*first, *first)

are convertible to T[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12763)

*Preconditions*: 

- [(4.1)](#4.1)

  T meets the [*Cpp17MoveConstructible*](utility.arg.requirements#:Cpp17MoveConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [31](utility.arg.requirements#tab:cpp17.moveconstructible "Table 31: Cpp17MoveConstructible requirements")) requirements[.](#4.1.sentence-1)

- [(4.2)](#4.2)

  binary_op neither invalidates iterators or subranges,
 nor modifies elements in
 the ranges [first, last] or [result, result + (last - first)][.](#4.2.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12774)

*Effects*: For each integer K in [0, last - first)
assigns through result + K the value of:*GENERALIZED_NONCOMMUTATIVE_SUM*( binary_op, init, *(first + 0), *(first + 1), …, *(first + K - 1))

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12783)

*Returns*: The end of the resulting range beginning at result[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12787)

*Complexity*: O(last - first) applications of binary_op[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12791)

*Remarks*: result may be equal to first[.](#8.sentence-1)

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12795)

[*Note [1](#note-1)*:

The difference between exclusive_scan and inclusive_scan is
that exclusive_scan excludes the ith input element
from the ith sum[.](#9.sentence-1)

If binary_op is not mathematically associative,
the behavior of exclusive_scan can be nondeterministic[.](#9.sentence-2)

— *end note*]