| 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.
|
| (until C++11) |
|
| (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 signature of the function should be equivalent to the following:
The signature does not need to have |
| Type requirements | ||
- InputIt must meet the requirements of InputIterator. | ||
- T must meet the requirements of CopyAssignable and CopyConstructible. | ||
Return value
Notes
Although std::accumulate performs left fold by default, right fold may be achieved by using reverse iterators, e.g. std::accumulate(v.rbegin(), v.rend(), init, binop).
Possible implementation
| First version |
|---|
template<class InputIt, class T>
T accumulate(InputIt first, InputIt last, T init)
{
for (; first != last; ++first) {
init = init + *first;
}
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(init, *first);
}
return init;
} |
Example
#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>());
std::string s = std::accumulate(std::begin(v), std::end(v), std::string{},
[](const std::string& a, int b) {
return a.empty() ? std::to_string(b)
: a + '-' + std::to_string(b);
});
std::cout << "sum: " << sum << '\n'
<< "product: " << product << '\n'
<< "dash-separated string: " << s << '\n';
}Output:
sum: 55 product: 3628800 dash-separated string: 1-2-3-4-5-6-7-8-9-10
See also
| computes the differences between adjacent elements in a range (function template) | |
| computes the inner product of two ranges of elements (function template) | |
| computes the partial sum of a range of elements (function template) | |
| reduce
(parallelism TS) | similar to std::accumulate, except out of order (function template) |
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