std::extent - cppreference.com

De cppreference.com

Definido no cabeçalho `<type_traits>`

`template< class T, unsigned N = 0> struct extent;`		(desde C++11)

If T is an array type, provides the member constant value equal to the number of elements along the Nth 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.

Herdado de std::integral_constant

Member constants


	the number of elements along the `N`th dimension of `T` (membro estático público constante)

Member functions


	converte o objeto em `std::size_t`, retorna `value` Original: converts the object to `std::size_t`, returns `value` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (função pública membro)

Member types


Tipo Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`value_type`	`std::size_t`

`type`	`std::integral_constant<std::size_t, value>`

Possível implementação

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::integral_constant<std::size_t, std::extent<T, N-1>::value> {};

template<class T, std::size_t N>
struct extent<T[N], 0> : std::integral_constant<std::size_t, N> {};

template<class T, std::size_t I, unsigned N>
struct extent<T[I], N> : std::integral_constant<std::size_t, std::extent<T, N-1>::value> {};

Exemplo

#include <iostream>
#include <type_traits>

int main()
{
    std::cout << std::extent<int[3]>::value << '\n';
    std::cout << std::extent<int[3][4]>::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';
}

Saída:

Veja também


is_array (C++11)	verifica se o tipo é um tipo de matriz Original: checks if a type is an array type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (modelo de classe) [edit]

rank (C++11)	obtém o número de dimensões de um tipo de matriz Original: obtains the number of dimensions of an array type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (modelo de classe) [edit]

remove_extent (C++11)	remove uma medida do tipo matriz dada Original: removes one extent from the given array type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (modelo de classe) [edit]

remove_all_extents (C++11)	removes all extents from the given array type (modelo de classe) [edit]