std::uninitialized_copy_n(3)

NAME
std::uninitialized_copy_n - std::uninitialized_copy_n

Synopsis
   Defined in header <memory>
   template< class InputIt, class Size, class NoThrowForwardIt >
   NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count, (1) (since C++11)
                        NoThrowForwardIt d_first );
   template< class ExecutionPolicy, class ForwardIt,
             class Size, class NoThrowForwardIt >
   NoThrowForwardIt uninitialized_copy_n( ExecutionPolicy&& policy, (2) (since C++17)
                        ForwardIt first, Size
   count,
                        NoThrowForwardIt d_first );
   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 + [0, n) overlaps with first + [0, n), the behavior is (since C++20)
   undefined.
   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)

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.

Return value
   Iterator to the element past the last element copied.

Complexity
   Linear in count.

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.

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;
    try
    {
        for (; count > 0; ++first, (void) ++current, --count)
            ::new (static_cast<void*>(std::addressof(*current))) T(*first);
    }
    catch (...)
    {
        for (; d_first != current; ++d_first)
            d_first->~T();
        throw;
    }
    return current; }

Example
// Run this code
 #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 << ' ';
         i->~basic_string<char>();
     }
     std::cout << '\n';
     std::return_temporary_buffer(p);
 }

Possible output:
 This is an example
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       the effect description used a for loop with
                       the iteration discards the value
   LWG 2133 C++98 expression ++d_first, ++first, --n, which of one operand to
                       results disable those ADLs
                       in argument-dependent lookups of operator,
   LWG 2433 C++11 this algorithm might be hijacked by uses std::addressof
                       overloaded operator&
   LWG 3870 C++20 this algorithm might create objects on a kept disallowed
                       const storage

See also
                        copies a range of objects to an uninitialized area of
   uninitialized_copy memory
                        (function template)
   ranges::uninitialized_copy_n copies a number of objects to an uninitialized area of
   (C++20) memory
                        (niebloid)