std::rank

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Defined in header <type_traits>
template< class T >
struct rank;
(since C++11)

If T is an array type, provides the member constant value equal to the number of dimensions of the array. For any other type, value is 0.

Contents

[edit] Helper variable template

template< class T >
constexpr std::size_t rank_v = rank<T>::value;
(since C++17)

Inherited from std::integral_constant

Member constants

value
[static]
the number of dimensions of T or zero
(public static member constant)

Member functions

operator std::size_t
converts the object to std::size_t, returns value
(public member function)
operator()
(C++14)
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

template<class T>
struct rank : public std::integral_constant<std::size_t, 0> {};
 
template<class T>
struct rank<T[]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};
 
template<class T, std::size_t N>
struct rank<T[N]> : public std::integral_constant<std::size_t, rank<T>::value + 1> {};

[edit] Example

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

Output:

3
4
0

[edit] See also

(C++11)
checks if a type is an array type
(class template)
(C++11)
obtains the size of an array type along a specified dimension
(class template)
removes one extent from the given array type
(class template)
removes all extents from the given array type
(class template)
(library fundamentals TS)
variable template alias of std::rank::value
(variable template)