std::extent
From cppreference.com
Defined in header <type_traits>
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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.
Helper variable template
template< class T, unsigned N = 0 > inline constexpr std::size_t extent_v = extent<T, N>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
value [static] |
the number of elements along the N th dimension of T (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, 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> {}; |
Example
Run this code
#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
See also
(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) |