< cpp‎ | memory
Dynamic memory management
Uninitialized storage
(deprecated since c++17)
(deprecated since c++17)
(deprecated since c++17)
Garbage collection support
C Library
Low level memory management
Defined in header <memory>
template< class InputIt, class Size, class ForwardIt >
ForwardIt uninitialized_copy_n( InputIt first, Size count, ForwardIt d_first);
(1) (since C++11)
template< class ExecutionPolicy, class InputIt, class Size, class ForwardIt >
ForwardIt uninitialized_copy_n( ExecutionPolicy&& policy, InputIt first, Size count, ForwardIt d_first);
(2) (since C++17)
1) Copies count elements from a range beginning at first to an uninitialized memory area beginning at d_first as if by
for ( ; n > 0; ++d_first, (void) ++first, --n)
   ::new (static_cast<void*>(std::addressof(*d_first)))
      typename iterator_traits<ForwardIt>::value_type(*first);
If an exception is thrown during the initialization, the function has no effects.
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 the elements to copy
d_first - 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.
ForwardIt must meet the requirements of ForwardIterator.
No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions.

[edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

Linear in count.

[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 ForwardIt>
ForwardIt uninitialized_copy_n(InputIt first, Size count, ForwardIt d_first)
    typedef typename std::iterator_traits<ForwardIt>::value_type Value;
    ForwardIt current = d_first;
    try {
        for (; count > 0; ++first, (void) ++current, --count) {
            ::new (static_cast<void*>(std::addressof(*current))) Value(*first);
    } catch (...) {
        for (; d_first != current; ++d_first) {
    return current;

[edit] Example

#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>
#include <vector>
int main()
    std::vector<std::string> v = {"This", "is", "an", "example"};
    std::string* p;
    std::size_t sz;
    std::tie(p, sz)  = std::get_temporary_buffer<std::string>(v.size());
    sz = std::min(sz, v.size());
    std::uninitialized_copy_n(v.begin(), sz, p);
    for (std::string* i = p; i != p+sz; ++i) {
        std::cout << *i << ' ';


This is an example

[edit] See also

copies a range of objects to an uninitialized area of memory
(function template) [edit]
parallelized version of std::uninitialized_copy_n
(function template) [edit]