# std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::unordered_multiset

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< cpp‎ | container‎ | unordered multiset

unordered_multiset() : unordered_multiset( size_type(/*implementation-defined*/) ) {} explicit unordered_multiset( size_type bucket_count, const Hash& hash = Hash(), const key_equal& equal = key_equal(), const Allocator& alloc = Allocator() ); | (1) | (since C++11)
unordered_multiset( size_type bucket_count, const Allocator& alloc ) : unordered_multiset(bucket_count, Hash(), key_equal(), alloc) {} unordered_multiset( size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_multiset(bucket_count, hash, key_equal(), alloc) {} | (1) | (since C++14)
explicit unordered_multiset( const Allocator& alloc ); | (1) | (since C++11)
template< class InputIt > unordered_multiset( InputIt first, InputIt last, size_type bucket_count = /*implementation-defined*/, const Hash& hash = Hash(), const key_equal& equal = key_equal(), const Allocator& alloc = Allocator() ); | (2) | (since C++11)
template< class InputIt > unordered_multiset( InputIt first, InputIt last, size_type bucket_count, const Allocator& alloc ) : unordered_multiset(first, last, bucket_count, Hash(), key_equal(), alloc) {} | (2) | (since C++14)
template< class InputIt > unordered_multiset( InputIt first, InputIt last, size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_multiset(first, last, bucket_count, hash, key_equal(), alloc) {} | (2) | (since C++14)
unordered_multiset( const unordered_multiset& other ); | (3) | (since C++11)
unordered_multiset( const unordered_multiset& other, const Allocator& alloc ); | (3) | (since C++11)
unordered_multiset( unordered_multiset&& other ); | (4) | (since C++11)
unordered_multiset( unordered_multiset&& other, const Allocator& alloc ); | (4) | (since C++11)
unordered_multiset( std::initializer_list <value_type> init, size_type bucket_count = /*implementation-defined*/, const Hash& hash = Hash(), const key_equal& equal = key_equal(), const Allocator& alloc = Allocator() ); | (5) | (since C++11)
unordered_multiset( std::initializer_list <value_type> init, size_type bucket_count, const Allocator& alloc ) : unordered_multiset(init, bucket_count, Hash(), key_equal(), alloc) {} | (5) | (since C++14)
unordered_multiset( std::initializer_list <value_type> init, size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_multiset(init, bucket_count, hash, key_equal(), alloc) {} | (5) | (since C++14)

Constructs new container from a variety of data sources. Optionally uses user supplied `bucket_count` as a minimal number of buckets to create, `hash` as the hash function, `equal` as the function to compare keys and `alloc` as the allocator.

1) Constructs empty container. Sets `max_load_factor()` to 1.0. For the default constructor, the number of buckets is implementation-defined.
2) constructs the container with the contents of the range `[first, last)`. Sets `max_load_factor()` to 1.0.
3) copy constructor. Constructs the container with the copy of the contents of `other`, copies the load factor, the predicate, and the hash function as well. If `alloc` is not provided, allocator is obtained by calling std::allocator_traits <allocator_type>::select_on_container_copy_construction(other.get_allocator()).
4) move constructor. Constructs the container with the contents of `other` using move semantics. If `alloc` is not provided, allocator is obtained by move-construction from the allocator belonging to `other`.
5) constructs the container with the contents of the initializer list `init`, same as unordered_multiset(init.begin(), init.end()).

### Parameters

alloc | - | allocator to use for all memory allocations of this container
bucket_count | - | minimal number of buckets to use on initialization. If it is not specified, implementation-defined default value is used
hash | - | hash function to use
equal | - | comparison function to use for all key comparisons of this container
first, last | - | the range to copy the elements from
other | - | another container to be used as source to initialize the elements of the container with
init | - | initializer list to initialize the elements of the container with
Type requirements
- `InputIt` must meet the requirements of LegacyInputIterator.

### Complexity

1) constant
2) average case linear worst case quadratic in distance between `first` and `last`
3) linear in size of `other`
4) constant. If `alloc` is given and alloc != other.get_allocator(), then linear.
5) average case linear worst case quadratic in size of `init`

### Exceptions

Calls to `Allocator::allocate` may throw.

### Notes

After container move construction (overload (4)), references, pointers, and iterators (other than the end iterator) to `other` remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in §23.2.1[container.requirements.general]/12, and a more direct guarantee is under consideration via LWG 2321.

### Example

| This section is incomplete Reason: no example

### 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 2193 | C++11 | the default constructor is explicit | made non-explicit

### See also

operator= | assigns values to the container (public member function)

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