# std::uninitialized_move

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Defined in header `<memory>` |  |
template< class InputIt, class NoThrowForwardIt > NoThrowForwardIt uninitialized_move( InputIt first, InputIt last, NoThrowForwardIt d_first ); | (1) | (since C++17)
template< class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt > NoThrowForwardIt uninitialized_move( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, NoThrowForwardIt d_first ); | (2) | (since C++17)

1) Moves elements from the range `[`first`,` last`)` to an uninitialized memory area beginning at d_first as if by
for (; first != last; ++d_first, (void) ++first)
::new (static_cast<void*>(std::addressof(*d_first)))
typename std::iterator_traits<NoThrowForwardIt>::value_type(std::move(*first));
If an exception is thrown during the initialization, some objects in `[`first`,` last`)` are left in a valid but unspecified state, and the objects already constructed are destroyed in an unspecified order.

If d_first`+` `[`​0​`,` std::distance(first, last)`)` overlaps with `[`first`,` last`)`, the behavior is undefined. | (since C++20)

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. | (until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. | (since C++20)

### Parameters

first, last | - | the range of the elements to move
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 moved.

### Complexity

Linear in the distance between first and last.

### 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 NoThrowForwardIt>
    NoThrowForwardIt uninitialized_move(InputIt first, InputIt last, NoThrowForwardIt d_first)
    {
        using Value = typename std::iterator_traits<NoThrowForwardIt>::value_type;
        NoThrowForwardIt current = d_first;
        try
        {
            for (; first != last; ++first, (void) ++current)
                ::new (static_cast<void*>(std::addressof(*current))) Value(std::move(*first));
            return current;
        }
        catch (...)
        {
            std::destroy(d_first, current);
            throw;
        }
    }

### 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[]{"Home", "Work!"};
        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(std::begin(in), std::end(in), 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: "Home" "Work!"
    after move, in: "" ""
    after move, out: "Home" "Work!"

### 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

### See also

uninitialized_copy | copies a range of objects to an uninitialized area of memory (function template)
uninitialized_move_n (C++17) | moves a number of objects to an uninitialized area of memory (function template)
ranges::uninitialized_move (C++20) | moves a range of objects to an uninitialized area of memory (niebloid)

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