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.
template< class T > inline constexpr std::size_t rank_v = rank<T>::value; | (since C++17) |
| value
[static] | the number of dimensions of T or zero (public static member constant) |
| operator std::size_t | converts the object to std::size_t, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | std::size_t |
type | std::integral_constant<std::size_t, value> |
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> {}; |
#include <type_traits>
int main()
{
static_assert(
std::rank<int>{} == 0
&& std::rank<int[5]>{} == 1
&& std::rank<int[5][5]>{} == 2
&& std::rank<int[][5][5]>{} == 3 );
[[maybe_unused]] int ary[][3] = {{1, 2, 3}};
// The reason of rank of "ary[0]" is calculated as 0
static_assert(std::rank_v<decltype(ary[0])> == 0);
// 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
static_assert(std::rank_v<std::remove_cvref_t<decltype(ary[0])>> == 1);
}|
(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) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/types/rank