Defined in header <algorithm>
template< class InputIt, class Size, class OutputIt >
OutputIt copy_n( InputIt first, Size count, OutputIt result );
(1) (since C++11)
template< class ExecutionPolicy, class ForwardIt1, class Size, class ForwardIt2 >
ForwardIt2 copy_n( ExecutionPolicy&& policy, ForwardIt1 first, Size count, ForwardIt2 result );
(2) (since C++17)
1) Copies exactly count values from the range beginning at first to the range beginning at result, if count>0. Does nothing otherwise.
2) Same as (1), but executed according to policy. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true


first - the beginning of the range of elements to copy from
count - number of the elements to copy
result - the beginning of the destination range
policy - the execution policy to use. See execution policy for details.
Type requirements
-InputIt must meet the requirements of InputIterator.
-OutputIt must meet the requirements of OutputIterator.
-ForwardIt1, ForwardIt2 must meet the requirements of ForwardIterator.

Return value

Iterator in the destination range, pointing past the last element copied if count>0 or result otherwise.


Exactly count assignments, if count>0.


The overload with a template parameter named ExecutionPolicy reports errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the three 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.

Possible implementation

template< class InputIt, class Size, class OutputIt>
OutputIt copy_n(InputIt first, Size count, OutputIt result)
    if (count > 0) {
        *result++ = *first;
        for (Size i = 1; i < count; ++i) {
            *result++ = *++first;
    return result;


#include <iostream>
#include <string>
#include <algorithm>
#include <iterator>
int main()
    std::string in = "1234567890";
    std::string out;
    std::copy_n(in.begin(), 4, std::back_inserter(out));
    std::cout << out << '\n';



See also

copies a range of elements to a new location
(function template)

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