[valarray.cons]

# 29 Numerics library [[numerics]](./#numerics)

## 29.6 Numeric arrays [[numarray]](numarray#valarray.cons)

### 29.6.2 Class template valarray [[template.valarray]](template.valarray#valarray.cons)

#### 29.6.2.2 Constructors [valarray.cons]

[ð](#lib:valarray,constructor)

`valarray();
`

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7333)

*Effects*: Constructs a valarray that has zero length[.](#1.sentence-1)[249](#footnote-249 "This default constructor is essential, since arrays of valarray can be useful. After initialization, the length of an empty array can be increased with the resize member function.")

[ð](#lib:valarray,constructor_)

`explicit valarray(size_t n);
`

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7354)

*Effects*: Constructs a valarray that has length n[.](#2.sentence-1)

Each element of the array is [value-initialized](dcl.init#def:value-initialization "9.5 Initializers [dcl.init]")[.](#2.sentence-2)

[ð](#lib:valarray,constructor__)

`valarray(const T& v, size_t n);
`

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7366)

*Effects*: Constructs a valarray that has length n[.](#3.sentence-1)

Each element of the array is initialized with v[.](#3.sentence-2)

[ð](#lib:valarray,constructor___)

`valarray(const T* p, size_t n);
`

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7379)

*Preconditions*: [p, p + n) is a valid range[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7383)

*Effects*: Constructs a valarray that has length n[.](#5.sentence-1)

The values of the elements of the array are initialized with the
firstn values pointed to by the first argument[.](#5.sentence-2)[250](#footnote-250 "This constructor is the preferred method for converting a C array to a valarray object.")

[ð](#lib:valarray,constructor____)

`valarray(const valarray& v);
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7404)

*Effects*: Constructs a valarray that has the same length as v[.](#6.sentence-1)

The elements are initialized with the values of the corresponding
elements of v[.](#6.sentence-2)[251](#footnote-251 "This copy constructor creates a distinct array rather than an alias. Implementations in which arrays share storage are permitted, but they would need to implement a copy-on-reference mechanism to ensure that arrays are conceptually distinct.")

[ð](#lib:valarray,constructor_____)

`valarray(valarray&& v) noexcept;
`

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7424)

*Effects*: Constructs a valarray that has the same length as v[.](#7.sentence-1)

The elements are initialized with the values of the corresponding
elements of v[.](#7.sentence-2)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7430)

*Complexity*: Constant[.](#8.sentence-1)

[ð](#lib:valarray,constructor______)

`valarray(initializer_list<T> il);
`

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7441)

*Effects*: Equivalent to valarray(il.begin(), il.size())[.](#9.sentence-1)

[ð](#lib:valarray,constructor_______)

`valarray(const slice_array<T>&);
valarray(const gslice_array<T>&);
valarray(const mask_array<T>&);
valarray(const indirect_array<T>&);
`

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7455)

These conversion constructors convert one of the four reference templates
to avalarray[.](#10.sentence-1)

[ð](#lib:valarray,destructor)

`~valarray();
`

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7467)

*Effects*: The destructor is applied to every element of*this;
an implementation may return all allocated memory[.](#11.sentence-1)

[249)](#footnote-249)[249)](#footnoteref-249)

This default constructor is essential,
since arrays ofvalarray can be useful[.](#footnote-249.sentence-1)

After initialization, the length of an empty array can be increased with theresize member function[.](#footnote-249.sentence-2)

[250)](#footnote-250)[250)](#footnoteref-250)

This constructor is the
preferred method for converting a C array to avalarray object[.](#footnote-250.sentence-1)

[251)](#footnote-251)[251)](#footnoteref-251)

This copy constructor creates
a distinct array rather than an alias[.](#footnote-251.sentence-1)

Implementations in which arrays share storage are permitted, but they
would need to implement a copy-on-reference mechanism to ensure that arrays are
conceptually distinct[.](#footnote-251.sentence-2)
