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    std::uninitialized_move_n

    From cppreference.com
     
    C++
     
    Memory management library
    (exposition only*)
    Allocators
    Uninitialized memory algorithms
    Constrained uninitialized memory algorithms
    Memory resources
    Uninitialized storage (until C++20)
    (until C++20*)
    (until C++20*)
    (until C++20*)

    Garbage collector support (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)
    (C++11)(until C++23)
     
    Defined in header <memory>
    template< class InputIt, class Size, class NoThrowForwardIt > std::pair<InputIt, NoThrowForwardIt> uninitialized_move_n( InputIt first, Size count, NoThrowForwardIt d_first );
    		 (1) (since C++17)
    (constexpr since C++26)
    template< class ExecutionPolicy, class ForwardIt, class Size, class NoThrowForwardIt > std::pair<ForwardIt, NoThrowForwardIt> uninitialized_move_n( ExecutionPolicy&& policy, ForwardIt first, Size count, NoThrowForwardIt d_first );
    		 (2) (since C++17)
    1) Copies the elements from first + [0, count) (using move semantics if supported) to an uninitialized memory area beginning at d_first as if by
    See More

    for (; count > 0; ++d_first, (void) ++first, --count)
        ::new (voidify(*d_first))
            typename std::iterator_traits<NoThrowForwardIt>::value_type(/* value */);
    return {first, d_first};

    where /* value */ is std::move(*first) if *first is of an lvalue reference type, or *first otherwise.
    If an exception is thrown during the initialization, some objects in first + [0, count) are left in a valid but unspecified state, and the objects already constructed are destroyed in an unspecified order.
    2) Same as (1), but executed according to policy.
    This overload participates in overload resolution only if all following conditions are satisfied:

    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)


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

    		(since C++20)

    Parameters

    first - the beginning of the range of the elements to move
    d_first - the beginning of the destination range
    count - the number of elements to move
    policy - the execution policy to use
    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

    As described above.

    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.

    Notes

    When the input iterator deferences to an rvalue, the behavior of std::uninitialized_move_n is same as std::uninitialized_copy_n.

    Feature-test macro Value Std Feature
    __cpp_lib_raw_memory_algorithms 202411L (C++26) constexpr for specialized memory algorithms, (1)

    Possible implementation

    template<class InputIt, class Size, class NoThrowForwardIt>
constexpr std::pair<InputIt, NoThrowForwardIt>
    uninitialized_move_n(InputIt first, Size count, NoThrowForwardIt d_first)
{
    using ValueType = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = d_first;
    try
    {
        for (; count > 0; ++first, (void) ++current, --count) {
            auto addr = static_cast<void*>(std::addressof(*current));
            if constexpr (std::is_lvalue_reference_v<decltype(*first)>)
                ::new (addr) ValueType(std::move(*first));
            else
                ::new (addr) ValueType(*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 retroactively 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 storage kept disallowed
    LWG 3918 C++17 additional temporary materialization was required
    when the input iterator deferences to a prvalue     		copies the element in this case

    See also

    (C++17)
    		 moves a range of objects to an uninitialized area of memory
    (function template) [edit]
    (C++11)
    		 copies a number of objects to an uninitialized area of memory
    (function template) [edit]
    (C++20)
    		 moves a number of objects to an uninitialized area of memory
    (algorithm function object)[edit]