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std::rank(3) C++ Standard Libary std::rank(3) NAME std::rank - std::rank Synopsis Defined in header <type_traits> template< class T > (since C++11) struct rank; 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 > (since C++17) inline constexpr std::size_t rank_v = rank<T>::value; Inherited from std::integral_constant Member constants value the number of dimensions of T or zero [static] (public static member constant) Member functions operator std::size_t converts the object to std::size_t, returns value (public member function) operator() returns value (C++14) (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 <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<de- cltype(ary[0])>>::value << '\n'; } Output: 0 1 2 3 0 1 See also is_array checks if a type is an array type (C++11) (class template) extent obtains the size of an array type along a speci- fied dimension (C++11) (class template) remove_extent removes one extent from the given array type (C++11) (class template) remove_all_extents removes all extents from the given array type (C++11) (class template) http://cppreference.com 2022.07.31 std::rank(3)
NAME | Synopsis | Member constants | Member functions | Member types | Possible implementation | Example | Output: | See also
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