Defined in header <type_traits> | ||
---|---|---|
template< class T, unsigned N = 0> struct extent; | (since C++11) |
If T
is an array type, provides the member constant value
equal to the number of elements along the N
th dimension of the array, if N
is in [0, std::rank<T>::value)
. For any other type, or if T
is array of unknown bound along its first dimension and N
is 0, value
is 0.
template< class T, unsigned N = 0 > inline constexpr std::size_t extent_v = extent<T, N>::value; | (since C++17) |
value
[static] | the number of elements along the N th dimension of T (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, unsigned N = 0> struct extent : std::integral_constant<std::size_t, 0> {}; template<class T> struct extent<T[], 0> : std::integral_constant<std::size_t, 0> {}; template<class T, unsigned N> struct extent<T[], N> : std::extent<T, N-1> {}; template<class T, std::size_t I> struct extent<T[I], 0> : std::integral_constant<std::size_t, I> {}; template<class T, std::size_t I, unsigned N> struct extent<T[I], N> : std::extent<T, N-1> {}; |
#include <iostream> #include <type_traits> int main() { std::cout << std::extent<int[3]>::value << '\n'; //< default dimension is 0 std::cout << std::extent<int[3][4], 0>::value << '\n'; std::cout << std::extent<int[3][4], 1>::value << '\n'; std::cout << std::extent<int[3][4], 2>::value << '\n'; std::cout << std::extent<int[]>::value << '\n'; const auto ext = std::extent<int[9]>{}; std::cout << ext << '\n'; //< implicit conversion to std::size_t const int ints[] = {1,2,3,4}; std::cout << std::extent<decltype(ints)>::value << '\n'; //< array size }
Output:
3 3 4 0 0 9 4
(C++11) | checks if a type is an array type (class template) |
(C++11) | obtains the number of dimensions of an array type (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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