< 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 InputIt, class Size, class OutputIt >
OutputIt copy_n( ExecutionPolicy&& policy, InputIt first, Size count, OutputIt 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 does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true


[edit] Parameters

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.

[edit] Return value

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

[edit] Complexity

Exactly count assignments, if count>0.

[edit] Exceptions

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, std::terminate is called.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] 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;

[edit] Example

#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';



[edit] See also

copies a range of elements to a new location
(function template)
parallelized version of std::copy_n
(function template)