public member function
<unordered_map>
template <class... Args>
iterator emplace_hint ( const_iterator position, Args&&... args );
Construct and insert element with hint
Inserts a new element in the unordered_multimap container. This new element is constructed in place using args as the arguments for the element's constructor. position points to a location in the container suggested as a hint on where to start the search for its insertion point (the container may or may not use this suggestion to optimize the insertion operation).
This effectively increases the container size by one.
A similar member function exists, insert, which either copies or moves an existing object into the container, and may also take a position hint.
Parameters
- position
- Position suggested as a hint for the insertion operation. This value may be used by the container to optimize the operation.
Member type const_iterator is a forward iterator type.
- args
Arguments used to construct a new object of the mapped type for the inserted element.
Arguments forwarded to construct the new element (of type
pair<const key_type, mapped_type>).
This can be one of:
- Two arguments: one for the
key, the other for the
mapped value.
- A single argument of a
pair type with a value for the
key as first member, and a value for the
mapped value as second.
-
piecewise_construct as first argument, and two additional arguments with
tuples to be forwarded as arguments for the
key value and for the
mapped value respectivelly.
See
pair::pair for more info.
Return value
An iterator to the newly inserted element.
Member type iterator is a forward iterator.
The storage for the new element is allocated using allocator_traits<allocator_type>::construct(), which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Complexity
Average case: constant.
Worst case: linear in container size.
May trigger a rehash (not included).
Iterator validity
On most cases, all iterators in the container remain valid after the insertion. The only exception being when the growth of the container forces a rehash. In this case, all iterators in the container are invalidated.
A rehash is forced if the new container size after the insertion operation would increase above its capacity threshold (calculated as the container's bucket_count multiplied by its max_load_factor).
References remain valid in all cases, even after a rehash.