std::uninitialized_move_n

 

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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 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 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}; }

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)