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std::extent

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Defined in header <type_traits>
template< class T, unsigned N = 0>
struct extent;
(since C++11)

If T is an array type, provides the member constant value equal to the number of elements along the Nth dimension of the array, if N is in [0, std::rank<T>::value). For any other type, or if T is array of unknown bound along its first dimension and N is 0, value is 0.

Contents

Inherited from std::integral_constant

Member constants

value
[static]
the number of elements along the Nth dimension of T
(public static member constant)

Member functions

operator std::size_t
converts the object to std::size_t, returns value
(public member function)

Member types

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

[edit] Possible implementation

[edit] Example

#include <iostream>
#include <type_traits>
 
int main()
{
    std::cout << std::extent<int[3]>::value << '\n';
    std::cout << std::extent<int[3][4]>::value << '\n';
    std::cout << std::extent<int[3][4],1>::value << '\n';
    std::cout << std::extent<int[3][4],2>::value << '\n';
    std::cout << std::extent<int[]>::value << '\n';
}

Output:

3
3
4
0
0

[edit] See also

(C++11)
checks if a type is an array type
(class template) [edit]
(C++11)
obtains the number of dimensions of an array type
(class template) [edit]
removes one extent from the given array type
(class template) [edit]
removes all extents from the given array type
(class template) [edit]