std::unordered_map emplace_hint() method

since C++11

// Non const version only
template <class... Args>
iterator emplace_hint( const_iterator hint, Args&&... args );

Inserts a new element to the container, using hint as a suggestion where the element should go. The element is constructed in-place, i.e. no copy or move operations are performed.

The constructor of the element type (value_type, that is, std::pair<const Key, T>) is called with exactly the same arguments as supplied to the function, forwarded with std::forward<Args>(args)....

Invalidation

If rehashing occurs due to the insertion, all iterators are invalidated.

Otherwise iterators are not affected. References are not invalidated.

Rehashing occurs only if the new number of elements is greater than max_load_factor() * bucket_count().

Parameters

• hint - iterator, used as a suggestion as to where to insert the new element
• args - arguments to forward to the constructor of the element

Return value

Returns an iterator to the newly inserted element. If the insertion failed because the element already exists, returns an iterator to the already existing element with the equivalent key.

Complexity

Average case, constant - O(1).
Worst case, linear in size of the container - O(size()).

Exceptions

If an exception is thrown by any operation, this function has no effect (strong exception guarantee).

Examples

important

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