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std::extent

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C++
 
Утилиты библиотеки
 
Поддержка типов
Основные типы
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Basic types
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Основные типы
Исправлены типы целых ширину (C++11)
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is_same(C++11)
is_base_of(C++11)
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alignment_of(C++11)
rank(C++11)
extent(C++11)
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remove_cv
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Введите черта констант
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Type trait constants
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integral_constant(C++11)
 
Заголовочный файл <type_traits>
template< class T, unsigned N = 0>
struct extent;
 (начиная с 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.

Содержание

Унаследован от std::integral_constant

Member constants

value
[static]
 the number of elements along the Nth dimension of T
(public static константа-член)

Member functions

operator std::size_t
преобразует объект в std::size_t, возвращает value
Original:
converts the object to std::size_t, returns value
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(public функция-член)

Member types

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

[править] Возможная реализация

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> {};

[править] Пример

#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';
}

Вывод: 

3
3
4
0
0

[править] См. также

(C++11)
проверяет, является ли тип является типом массива
Original:
checks if a type is an array type
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(шаблон класса) [edit]
(C++11)
получает число измерений массива
Original:
obtains the number of dimensions of an array type
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(шаблон класса) [edit]
(C++11)
удаляет одну степень от данного типа массива
Original:
removes one extent from the given array type
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(шаблон класса) [edit]
(C++11)
 removes all extents from the given array type
(шаблон класса) [edit]
Источник — «http://ru.cppreference.com/mwiki/index.php?title=cpp/types/extent&oldid=31402»