< cpp‎ | algorithm
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations

Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
C library
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)