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std::uninitialized_move_n(3)  C++ Standard Libary std::uninitialized_move_n(3)

NAME
       std::uninitialized_move_n - std::uninitialized_move_n

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

	  std::pair<InputIt,				     NoThrowForwardIt>
       (1) (since C++17)
	      uninitialized_move_n( InputIt first, Size	count,

				    NoThrowForwardIt d_first );
	  template< class ExecutionPolicy, class ForwardIt,

		    class Size,	class NoThrowForwardIt >
	  std::pair<ForwardIt,				     NoThrowForwardIt>
       (2) (since C++17)
	      uninitialized_move_n( ExecutionPolicy&& policy, ForwardIt
	  first,

				    Size count,	NoThrowForwardIt d_first );

	  1) Moves count elements from a range beginning at first to an	unini-
       tialized	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<NoThrowFor-
       wardIt>::value_type(std::move(*first));
	  If an	exception is thrown during the initialization, some objects in
       first + [0, n)
	  are left in a	valid but unspecified state, and 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 par-
       ticipates 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 ele-
       ments to	move
	  d_first	     -		the beginning of the destination range
	  count		     -		the number of elements to move
	  policy	     -		the execution policy to	use. See  exe-
       cution 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 LegacyForwardItera-
       tor.
	  -
	  No increment,	assignment, comparison,	or indirection	through	 valid
       instances of
	  NoThrowForwardIt may throw exceptions.

Return value
	  A  pair  whose  first	element	is an iterator to the element past the
       last element moved
	  in the source	range, and whose second	element	is an iterator to  the
       element past the
	  last element moved in	the destination	range.

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::termi-
       nate 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>
       std::pair<InputIt, NoThrowForwardIt>
	   uninitialized_move_n(InputIt	 first,	 Size  count, NoThrowForwardIt
       d_first)	{
	   using    Value    =	  typename    std::iterator_traits<NoThrowFor-
       wardIt>::value_type;
	   NoThrowForwardIt current = d_first;
	   try
	   {
	       for (; count > 0; ++first, (void) ++current, --count)
		   ::new	(static_cast<void*>(std::addressof(*current)))
       Value(std::move(*first));
	   }
	   catch (...)
	   {
	       std::destroy(d_first, current);
	       throw;
	   }
	   return {first, current}; }

Example
       // Run this code

	#include <cstdlib>
	#include <iomanip>
	#include <iostream>
	#include <memory>
	#include <string>

	void print(auto	rem, auto first, auto last)
	{
	    for	(std::cout << rem; first != last; ++first)
		std::cout << std::quoted(*first) << ' ';
	    std::cout << '\n';
	}

	int main()
	{
	    std::string	in[]{"One", "Definition", "Rule"};
	    print("initially, in: ", std::begin(in), std::end(in));

	    if (
		constexpr auto sz = std::size(in);
		void*	 out	=     std::aligned_alloc(alignof(std::string),
       sizeof(std::string) * sz))
	    {
		try
		{
		    auto first{static_cast<std::string*>(out)};
		    auto last{first + sz};
		    std::uninitialized_move_n(std::begin(in), sz, first);

		    print("after move, in: ", std::begin(in), std::end(in));
		    print("after move, out: ", first, last);

		    std::destroy(first,	last);
		}
		catch (...)
		{
		    std::cout << "Exception!\n";
		}
		std::free(out);
	    }
	}

Possible output:
	initially, in: "One" "Definition" "Rule"
	after move, in:	"" "" ""
	after move, out: "One" "Definition" "Rule"

	  Defect reports

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

	     DR	      Applied	 to		    Behavior	as   published
       Correct behavior
	  LWG 3870 C++20      this algorithm might create objects on  a	 const
       kept disallowed
			      storage

See also
	  uninitialized_move		moves  a range of objects to an	unini-
       tialized	area of
	  (C++17)		       memory
				       (function template)
	  uninitialized_copy_n	       copies a	number of objects to an	unini-
       tialized	area of
	  (C++11)		       memory
				       (function template)
	  ranges::uninitialized_move_n moves a number of objects to an	unini-
       tialized	area of
	  (C++20)		       memory
				       (niebloid)

http://cppreference.com		  2024.06.10	  std::uninitialized_move_n(3)

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