[map.cons]

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

## 23.4 Associative containers [[associative]](associative#map.cons)

### 23.4.3 Class template map [[map]](map#cons)

#### 23.4.3.2 Constructors, copy, and assignment [map.cons]

[🔗](#lib:map,constructor)

`constexpr explicit map(const Compare& comp, const Allocator& = Allocator());
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11751)

*Effects*: Constructs an emptymap using the specified comparison object and allocator[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11757)

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

[🔗](#lib:map,constructor_)

`template<class InputIterator>
  constexpr map(InputIterator first, InputIterator last,
                const Compare& comp = Compare(), const Allocator& = Allocator());
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11770)

*Effects*: Constructs an emptymap using the specified comparison object and allocator,
and inserts elements from the range
[first, last)[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11778)

*Complexity*: Linear in N if the range
[first, last)
is already sorted with respect to comp and otherwise NlogN, where N is last - first[.](#4.sentence-1)

[🔗](#lib:map,constructor__)

`template<[container-compatible-range](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R>
  constexpr map(from_range_t, R&& rg, const Compare& comp = Compare(),
                const Allocator& = Allocator());
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11795)

*Effects*: Constructs an empty map using the specified comparison object and allocator,
and inserts elements from the range rg[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L11801)

*Complexity*: Linear in N if rg is already sorted with respect to comp and
otherwise NlogN, where N is ranges​::​distance(rg)[.](#6.sentence-1)