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[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 "23.2.2.1Introduction[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)