std::extents, std::dextents, std::dims

Defined in header <mdspan>

Defined in header `<mdspan>`
template< class IndexType, std::size_t... Extents > class extents;	(1)	(since C++23)
template< class IndexType, std::size_t Rank > using dextents = /* see below */	(2)	(since C++23)
template< std::size_t Rank, class IndexType = std::size_t > using dims = std::dextents<IndexType, Rank>;	(3)	(since C++26)

template< class IndexType, std::size_t... Extents >
class extents;

(1)

(since C++23)

template< class IndexType, std::size_t Rank >
using dextents = /* see below */

(2)

(since C++23)

template< std::size_t Rank, class IndexType = std::size_t >
using dims = std::dextents<IndexType, Rank>;

(3)

(since C++26)

1) Represents a multidimensional index space of rank equal to sizeof...(Extents).

2) A convenient alias template for an all-dynamic extents. Let d denote std::dynamic_extent, each specialization of it dextents<IndexType, Rank> is equivalent to extents<IndexType /*, d, d, ..., d*/> (i.e. d is repeated a total of Rank times).

3) A convenient alias template for an all-dynamic extents with std::size_t as the default index type.

Each specialization of extents models regular and is TriviallyCopyable.

Template parameters

IndexType	-	the type of each non-dynamic `Extents`. Shall be a signed or unsigned integer type. Otherwise, the program is ill-formed
Extents	-	represents extent (size of an integer interval) for each rank index. Each element of it is either equal to std::dynamic_extent (in this case, it represents a dynamic extent and the extent size will be determined dynamically), or is representable as a value of type `IndexType` (then it represents a static extent and the extent size is just the value of it), or else the program is ill-formed
Rank	-	denotes the rank of an all-dynamic `extents`

Member types

Member type	Definition
`index_type`	`IndexType`
`size_type`	std::make_unsigned_t<index_type>
`rank_type`	`std::size_t`

Data members

Member name	Definition
std::array<index_type,rank_dynamic()> `dynamic-extents` (private)	An array which stores the size of each dynamic extents. (exposition-only member object*)

Member functions

(constructor)	constructs an `extents` (public member function)
Observers
rank [static]	returns the static rank of an `extents` (public static member function)
rank_dynamic [static]	returns the dynamic rank of an `extents` (public static member function)
static_extent [static]	returns static extent size of an `extents` at a certain rank index (public static member function)
extent	returns dynamic extent size of an `extents` at a certain rank index (public member function)
Helpers
fwd-prod-of-extents	returns the product of extent size in range `[`0`,` i`)` (exposition-only member function*)
rev-prod-of-extents	returns the product of extents size in range `[`i+1`,` rank()`)` (exposition-only member function*)
index-cast	casts the input into an integer type (exposition-only member function*)
dynamic-index (private)	returns the number of dynamic extents below a certain rank index (exposition-only member function*)
dynamic-index-inv (private)	returns the number `r` such that in range `[`0`,` r+1`)` there is exactly `i + 1` dynamic extents for a certain argument `i` (exposition-only member function*)

Non-member functions

operator==

(C++23)

compare underlying extents in each dimension of two extents
(function)

rank (C++11)	obtains the number of dimensions of an array type (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)

std::extents, std::dextents, std::dims

Template parameters

Member types

Data members

Member functions

Observers

Helpers

Non-member functions

Deduction guides(C++23)

Example

See also