23 Containers library [containers]

23.5 Unordered associative containers [unord]

23.5.4 Class template unordered_multimap [unord.multimap]

23.5.4.2 Constructors [unord.multimap.cnstr]

unordered_multimap() : unordered_multimap(size_type(see below)) { }
explicit unordered_multimap(size_type n,
                            const hasher& hf = hasher(),
                            const key_equal& eql = key_equal(),
                            const allocator_type& a = allocator_type());

Effects: Constructs an empty unordered_multimap using the specified hash function, key equality predicate, and allocator, and using at least n buckets.

For the default constructor, the number of buckets is implementation-defined.

max_load_factor() returns 1.0.

Complexity: Constant.

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template<class InputIterator>
  unordered_multimap(InputIterator f, InputIterator l,
                     size_type n = see below,
                     const hasher& hf = hasher(),
                     const key_equal& eql = key_equal(),
                     const allocator_type& a = allocator_type());
template<container-compatible-range<value_type> R>
  unordered_multimap(from_range_t, R&& rg,
                     size_type n = see below,
                     const hasher& hf = hasher(),
                     const key_equal& eql = key_equal(),
                     const allocator_type& a = allocator_type());
unordered_multimap(initializer_list<value_type> il,
                   size_type n = see below,
                   const hasher& hf = hasher(),
                   const key_equal& eql = key_equal(),
                   const allocator_type& a = allocator_type());

Effects: Constructs an empty unordered_multimap using the specified hash function, key equality predicate, and allocator, and using at least n buckets.

If n is not provided, the number of buckets is implementation-defined.

Then inserts elements from the range [f, l), rg, or il, respectively.

max_load_factor() returns 1.0.

Complexity: Average case linear, worst case quadratic.