std::rank

< cpp‎ | types

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.

The behavior of a program that adds specializations for rank or rank_v (since C++17) is undefined.

Helper variable template

template< class T > inline 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>{} << "\n\n";
 
    std::cout << std::rank<int[5]>{} << '\n';
    std::cout << std::rank<int[5][5]>{} << '\n';
    std::cout << std::rank<int[][5][5]>{} << '\n';
}

Output:

is_array (C++11)	checks if a type is an array type (class template)
extent (C++11)	obtains the size of an array type along a specified dimension (class template)
remove_extent (C++11)	removes one extent from the given array type (class template)
remove_all_extents (C++11)	removes all extents from the given array type (class template)