[class.slice]

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

## 29.6 Numeric arrays [[numarray]](numarray#class.slice)

### 29.6.4 Class slice [class.slice]

#### [29.6.4.1](#overview) Overview [[class.slice.overview]](class.slice.overview)

[🔗](#lib:slice)

namespace std {class slice {public: slice();
 slice(size_t, size_t, size_t);
 slice(const slice&);

 size_t start() const;
 size_t size() const;
 size_t stride() const; friend bool operator==(const slice& x, const slice& y); };}

[1](#overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8393)

The slice class represents a BLAS-like slice from an array[.](#overview-1.sentence-1)

Such a slice is specified by a starting index, a length, and a
stride[.](#overview-1.sentence-2)[252](#footnote-252 "BLAS stands for Basic Linear Algebra Subprograms. C++ programs can instantiate this class. See, for example, Dongarra, Du Croz, Duff, and Hammerling: A set of Level 3 Basic Linear Algebra Subprograms; Technical Report MCS-P1-0888, Argonne National Laboratory (USA), Mathematics and Computer Science Division, August, 1988.")

[252)](#footnote-252)[252)](#footnoteref-252)

BLAS stands for*Basic Linear Algebra Subprograms*[.](#footnote-252.sentence-1)

C++ programs can instantiate this class[.](#footnote-252.sentence-2)

See, for example,
Dongarra, Du Croz, Duff, and Hammerling:*A set of Level 3 Basic Linear Algebra Subprograms*;
Technical Report MCS-P1-0888,
Argonne National Laboratory (USA),
Mathematics and Computer Science Division,
August, 1988[.](#footnote-252.sentence-3)

#### [29.6.4.2](#cons.slice) Constructors [[cons.slice]](cons.slice)

[🔗](#lib:slice,constructor)

`slice();
slice(size_t start, size_t length, size_t stride);
`

[1](#cons.slice-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8420)

The default constructor is equivalent to slice(0, 0, 0)[.](#cons.slice-1.sentence-1)

A default constructor is provided only to permit the declaration of arrays of slices[.](#cons.slice-1.sentence-2)

The constructor with arguments for a slice takes a start, length, and stride
parameter[.](#cons.slice-1.sentence-3)

[2](#cons.slice-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8426)

[*Example [1](#cons.slice-example-1)*:

slice(3, 8, 2) constructs a slice which selects elements 3,5,7,…,17 from an array[.](#cons.slice-2.sentence-1)

— *end example*]

#### [29.6.4.3](#slice.access) Access functions [[slice.access]](slice.access)

[🔗](#lib:start,slice)

`size_t start() const;
size_t size() const;
size_t stride() const;
`

[1](#slice.access-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8444)

*Returns*: The start, length, or stride specified
by a slice object[.](#slice.access-1.sentence-1)

[2](#slice.access-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8449)

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

#### [29.6.4.4](#slice.ops) Operators [[slice.ops]](slice.ops)

[🔗](#lib:stride,slice_)

`friend bool operator==(const slice& x, const slice& y);
`

[1](#slice.ops-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L8462)

*Effects*: Equivalent to:return x.start() == y.start() && x.size() == y.size() && x.stride() == y.stride();