Class Template unordered_multiset

:idprefix: unordered_multiset_

`boost::unordered_multiset` — An unordered associative container that stores values. The same key can be stored multiple times.

Synopsis

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Description

*Template Parameters*

_Key_

`Key` must be https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container (i.e. `allocator_traits` can destroy it).

_Hash_

A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type `std::size_t`.

_Pred_

A binary function object that implements an equivalence relation on values of type `Key`. A binary function object that induces an equivalence relation on values of type `Key`. It takes two arguments of type `Key` and returns a value of type bool.

_Allocator_

An allocator whose value type is the same as the container's value type.

Allocators using https://en.cppreference.com/w/cpp/named_req/Allocator#Fancy_pointers[fancy pointers] are supported.

The elements are organized into buckets. Keys with the same hash code are stored in the same bucket and elements with equivalent keys are stored next to each other.

The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash.

Configuration macros

`BOOST_UNORDERED_ENABLE_SERIALIZATION_COMPATIBILITY_V0`