< cpp‎ | memory
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Garbage collection support
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)

Defined in header <memory>
template< class InputIt, class Size, class NoThrowForwardIt >

NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count,

                                       NoThrowForwardIt d_first );
(1) (since C++11)
template< class ExecutionPolicy, class ForwardIt,

          class Size, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy_n( ExecutionPolicy&& policy,
                                       ForwardIt first, Size count,

                                       NoThrowForwardIt 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 std::iterator_traits<NoThrowForwardIt>::value_type(*first);
If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.

If d_first + [0n) overlaps with first + [0n), the behavior is undefined.

(since C++20)
2) Same as (1), but executed according to policy. This overload participates in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)


[edit] Parameters

first - the beginning of the range of the elements to copy
count - the number of 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 LegacyInputIterator.
ForwardIt must meet the requirements of LegacyForwardIterator.
NoThrowForwardIt must meet the requirements of LegacyForwardIterator.
No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt 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 and ExecutionPolicy is one of the 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.

[edit] Possible implementation

template<class InputIt, class Size, class NoThrowForwardIt>
NoThrowForwardIt uninitialized_copy_n(InputIt first, Size count, NoThrowForwardIt d_first)
    using T = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = d_first;
        for (; count > 0; ++first, (void) ++current, --count)
            ::new (static_cast<void*>(std::addressof(*current))) T(*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 << ' ';
    std::cout << '\n';

Possible output:

This is an example

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2133 C++98 the effect description used a for loop with the iteration
expression ++d_first, ++first, --n, which results
in argument-dependent lookups of operator,
discards the value
of one operand to
disable those ADLs
LWG 2433 C++11 this algorithm might be hijacked by overloaded operator& uses std::addressof
LWG 3870 C++20 this algorithm might create objects on a const storage kept disallowed

[edit] See also

copies a range of objects to an uninitialized area of memory
(function template) [edit]
copies a number of objects to an uninitialized area of memory