Thegeneralized, noncommutative sum of a sequence of elements over a binary operationbinary_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 elementselem1 andelem2 from the sequence.
2. Calculatesbinary_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.

Givenbinary_op as the actual binary operation:

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

• For overloads(1-4), ifbinary_op(*first,*first) is not convertible to thevalue type ofdecltype(first), the program is ill-formed.

• For overloads(5,6), if any of the following values is not convertible toT, the program 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:

• For overloads(1-4), the value type ofdecltype(first) is notMoveConstructible.
• For overloads(5,6),T is notMoveConstructible.
• binary_op modifies any element of[first, last).
• binary_op invalidates any iterator or subrange of[first, last].

[edit]Parameters

[edit]Return value

Iterator to the element past the last element written.

[edit]Complexity

Given\(\scriptsize N\)N asstd::distance(first, last):

[edit]Exceptions

The overloads with a template parameter namedExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory,std::bad_alloc is thrown.

[edit]Example

#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<>{});}

Exclusive sum: 0 3 4 8 9 14 23 25Inclusive sum: 3 4 8 9 14 23 25 31 Exclusive product: 1 3 3 12 12 60 540 1080Inclusive product: 3 3 12 12 60 540 1080 6480

[edit]See also

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