std::accumulate

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library(C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library(C++11)

Atomic operations library(C++11)

Thread support library(C++11)

Filesystem library(C++17)

Technical Specifications

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Concepts and utilities: std::Sortable, std::projected, ...
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
is_execution_policy	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_3way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17)	uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17) compare_3way (C++20)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

Defined in header <numeric>
template<class InputIt, class T > T accumulate( InputIt first, InputIt last, T init );	(1)
template<class InputIt, class T, class BinaryOperation > T accumulate( InputIt first, InputIt last, T init,               BinaryOperation op );	(2)

Computes the sum of the given value init and the elements in the range [first, last). The first version uses operator+ to sum up the elements, the second version uses the given binary function op, both applying std::move to their operands on the left hand side(since C++20).

op must not have side effects.	(until C++11)
op must not invalidate any iterators, including the end iterators, nor modify any elements of the range involved, and also *last.	(since C++11)

Parameters

first, last	-	the range of elements to sum
init	-	initial value of the sum
op	-	binary operation function object that will be applied. The binary operator takes the current accumulation value a (initialized to init) and the value of the current element b. The signature of the function should be equivalent to the following:  Ret fun(const Type1 &a, const Type2 &b); The signature does not need to have const&. The type Type1 must be such that an object of type T can be implicitly converted to Type1. The type Type2 must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type2. The type Ret must be such that an object of type T can be assigned a value of type Ret. ​
Type requirements
- InputIt must meet the requirements of LegacyInputIterator.
- T must meet the requirements of CopyAssignable and CopyConstructible.

Return value

1) The sum of the given value and elements in the given range.

2) The result of left fold of the given range over op

Notes

std::accumulate performs a left fold. In order to perform a right fold, one must reverse the order of the arguments to the binary operator, and use reverse iterators.

Possible implementation

First version
template<class InputIt, class T> T accumulate(InputIt first, InputIt last, T init){for(; first != last;++first){ init = std::move(init)+*first;// std::move since C++20}return init;}
Second version
template<class InputIt, class T, class BinaryOperation> T accumulate(InputIt first, InputIt last, T init, BinaryOperation op){for(; first != last;++first){ init = op(std::move(init), *first);// std::move since C++20}return init;}

Example

Run this code

#include <iostream>#include <vector>#include <numeric>#include <string>#include <functional>   int main(){std::vector<int> v{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};   int sum = std::accumulate(v.begin(), v.end(), 0);   int product = std::accumulate(v.begin(), v.end(), 1, std::multiplies<int>());   auto dash_fold =[](std::string a, int b){return std::move(a)+'-'+std::to_string(b);};   std::string s = std::accumulate(std::next(v.begin()), v.end(), std::to_string(v[0]), // start with first element dash_fold);   // Right fold using reverse iteratorsstd::string rs = std::accumulate(std::next(v.rbegin()), v.rend(), std::to_string(v.back()), // start with last element dash_fold);   std::cout<<"sum: "<< sum <<'\n'<<"product: "<< product <<'\n'<<"dash-separated string: "<< s <<'\n'<<"dash-separated string (right-folded): "<< rs <<'\n';}

Output:

sum: 55 product: 3628800 dash-separated string: 1-2-3-4-5-6-7-8-9-10 dash-separated string (right-folded): 10-9-8-7-6-5-4-3-2-1

See also

adjacent_difference	computes the differences between adjacent elements in a range (function template)
inner_product	computes the inner product of two ranges of elements (function template)
partial_sum	computes the partial sum of a range of elements (function template)
reduce (C++17)	similar to std::accumulate, except out of order (function template)