[vector.cons]

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

## 23.3 Sequence containers [[sequences]](sequences#vector.cons)

### 23.3.13 Class template vector [[vector]](vector#cons)

#### 23.3.13.2 Constructors [vector.cons]

[ð](#lib:vector,constructor)

`constexpr explicit vector(const Allocator&) noexcept;
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L9992)

*Effects*: Constructs an empty vector, using the
specified allocator[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L9997)

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

[ð](#lib:vector,constructor_)

`constexpr explicit vector(size_type n, const Allocator& = Allocator());
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10008)

*Preconditions*: T is *Cpp17DefaultInsertable* into vector[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10012)

*Effects*: Constructs a vector with n default-inserted elements using the specified allocator[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10017)

*Complexity*: Linear in n[.](#5.sentence-1)

[ð](#lib:vector,constructor__)

`constexpr vector(size_type n, const T& value,
                 const Allocator& = Allocator());
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10029)

*Preconditions*: T is*Cpp17CopyInsertable* into vector[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10034)

*Effects*: Constructs a vector with n copies of value, using the specified allocator[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10039)

*Complexity*: Linear in n[.](#8.sentence-1)

[ð](#lib:vector,constructor___)

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

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10052)

*Effects*: Constructs a vector equal to the
range [first, last), using the specified allocator[.](#9.sentence-1)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10057)

*Complexity*: Makes only N calls to the copy constructor ofT (where N is the distance betweenfirst andlast)
and no reallocations ifInputIterator meets the *Cpp17ForwardIterator* requirements[.](#10.sentence-1)

It makes orderN calls to the copy constructor ofT and orderlogN reallocations if they are just input iterators[.](#10.sentence-2)

[ð](#lib:vector,constructor____)

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

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10085)

*Effects*: Constructs a vector object with the elements of the range rg,
using the specified allocator[.](#11.sentence-1)

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10090)

*Complexity*: Initializes exactly N elements
from the results of dereferencing successive iterators of rg,
where N is ranges​::​distance(rg)[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L10096)

Performs no reallocations if:

- [(13.1)](#13.1)

R models ranges​::​[approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]"), andranges​::​distance(rg) <= ranges​::​reserve_hint(rg) is true, or

- [(13.2)](#13.2)

R models ranges​::​[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") andR does not model ranges​::​[approximately_sized_range](range.approximately.sized#concept:approximately_sized_range "25.4.3 Approximately sized ranges [range.approximately.sized]")[.](#13.sentence-1)

Otherwise, performs order logN reallocations and
order N calls to the copy or move constructor of T[.](#13.sentence-2)
