# std::uninitialized_move_n

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< cpp‎ | memory

Defined in header `<memory>` |  |
template< class InputIt, class Size, class ForwardIt > std::pair<InputIt, ForwardIt> uninitialized_move_n( InputIt first, Size count, ForwardIt d_first ); | (1) | (since C++17)
template< class ExecutionPolicy, class InputIt, class Size, class ForwardIt > std::pair<InputIt, ForwardIt> uninitialized_move_n( ExecutionPolicy&& policy, InputIt first, Size count, ForwardIt d_first ); | (2) | (since C++17)

1) Moves `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<ForwardIt>::value_type(std::move(*first));

If an exception is thrown during the initialization, some objects in the source range 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 does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

### Parameters

first | - | the beginning of 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.
- No increment, assignment, comparison, or indirection through valid instances of `ForwardIt` 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::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 ForwardIt>
    std::pair<InputIt, ForwardIt> uninitialized_move_n(InputIt first, Size count, ForwardIt d_first)
    {
        typedef typename std::iterator_traits<ForwardIt>::value_type Value;
        ForwardIt current = d_first;
        try {
            for (; count > 0; ++first, (void) ++current, --count) {
                ::new (static_cast<void*>(std::addressof(*current))) Value(std::move(*first));
            }
        } catch (...) {
            for (; d_first != current; ++d_first) {
                d_first->~Value();
            }
            throw;
        }
        return {first, current};
    }

### Example

| This section is incomplete Reason: no example

### See also

uninitialized_move (C++17) | moves a range of objects to an uninitialized area of memory (function template)
uninitialized_copy_n (C++11) | copies a number of objects to an uninitialized area of memory (function template)

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