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std::extent

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Defined in header <type_traits>
template< class T, unsigned N = 0>
struct extent;
(a partir do 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.

Índice

Inherited from std::integral_constant

Member constants

value
[estática]
the number of elements along the Nth dimension of T
(membro estático público constante)

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operator std::size_t
converte o objeto em std::size_t, retorna value
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converts the object to std::size_t, returns value
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(função pública membro)

Member types

Tipo
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Type
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Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

[editar] 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> {};

[editar] 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';
}

Output:

3
3
4
0
0

[editar] Veja também

(C++11)
verifica se o tipo é um tipo de matriz
Original:
checks if a type is an array type
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(modelo de classe) [edit]
(C++11)
obtém o número de dimensões de um tipo de matriz
Original:
obtains the number of dimensions of an array type
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(modelo de classe) [edit]
remove uma medida do tipo matriz dada
Original:
removes one extent from the given array type
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(modelo de classe) [edit]
removes all extents from the given array type
(modelo de classe) [edit]