[unord.multimap.cnstr]

# 23 Containers library [[containers]](./#containers)

## 23.5 Unordered associative containers [[unord]](unord#multimap.cnstr)

### 23.5.4 Class template unordered_multimap [[unord.multimap]](unord.multimap#cnstr)

#### 23.5.4.2 Constructors [unord.multimap.cnstr]

[🔗](#lib:unordered_multimap,constructor)

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

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L14508)

*Effects*: Constructs an empty unordered_multimap using the
specified hash function, key equality predicate, and allocator, and
using at least n buckets[.](#1.sentence-1)

For the default constructor,
the number of buckets is implementation-defined[.](#1.sentence-2)

max_load_factor() returns 1.0[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L14517)

*Complexity*: Constant[.](#2.sentence-1)

[🔗](#lib:unordered_multimap,constructor_)

`template<class InputIterator>
  constexpr 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](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R>
  constexpr 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());
constexpr 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());
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L14541)

*Effects*: Constructs an empty unordered_multimap using the
specified hash function, key equality predicate, and allocator, and
using at least n buckets[.](#3.sentence-1)

If n is not
provided, the number of buckets is implementation-defined[.](#3.sentence-2)

Then
inserts elements from the range [f, l), rg, or il,
respectively[.](#3.sentence-3)

max_load_factor() returns 1.0[.](#3.sentence-4)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L14552)

*Complexity*: Average case linear, worst case quadratic[.](#4.sentence-1)