std::rank
From cppreference.com
| 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.
If the program adds specializations for std::rank or std::rank_v(since C++17), the behavior is undefined.
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
Run this code
#include <type_traits>
static_assert(std::rank<int>{} == 0);
static_assert(std::rank<int[5]>{} == 1);
static_assert(std::rank<int[5][5]>{} == 2);
static_assert(std::rank<int[][5][5]>{} == 3);
int main()
{
[[maybe_unused]] int ary[][3] = {{1, 2, 3}};
// The rank of reference type, e.g., ary[0], that is int(&)[3], is 0:
static_assert(std::rank_v<decltype(ary[0])> == 0);
static_assert(std::is_same_v<decltype(ary[0]), int(&)[3]>);
// The solution is to remove the reference type.
static_assert(std::rank_v<std::remove_cvref_t<decltype(ary[0])>> == 1);
}
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) |