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.
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';
[[maybe_unused]] int ary[][3]={ {1,2,3} };
// The reason of rank of "ary[0]" is calculated as 0
std::cout << std::rank<decltype(ary[0])>::value << '\n';
// is that rank cannot deal with reference type. i.e. int(&)[3]
static_assert(std::is_same_v<decltype(ary[0]), int(&)[3]>);
// The solution is to remove reference type
std::cout << std::rank<std::remove_cvref_t<decltype(ary[0])>>::value << '\n';
}
Output:
0 1 2 3 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) |
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