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std::rank

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.

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>

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> {};

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

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)
(C++11)
 removes one extent from the given array type
(class template)
(C++11)
 removes all extents from the given array type
(class template)
(library fundamentals TS)
 variable template alias of std::rank::value
(variable template)

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