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std::aligned_storage

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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)
Числовые пределы
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Numeric limits
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numeric_limits
С числовым ограничивает интерфейс
Время тип информации
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Runtime type information
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Тип черты
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Type traits
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Первичные категории типа
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Primary type categories
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is_void(C++11)
is_array(C++11)
is_pointer(C++11)
is_enum(C++11)
is_union(C++11)
is_class(C++11)
is_function(C++11)
is_object(C++11)
is_scalar(C++11)
is_compound(C++11)
is_integral(C++11)
is_floating_point(C++11)
is_fundamental(C++11)
is_arithmetic(C++11)
is_reference(C++11)
is_lvalue_reference(C++11)
is_rvalue_reference(C++11)
is_member_pointer(C++11)
is_member_object_pointer(C++11)
is_member_function_pointer(C++11)
Тип свойства
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Type properties
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is_const(C++11)
is_volatile(C++11)
is_pod(C++11)
is_empty(C++11)
is_polymorphic(C++11)
is_abstract(C++11)
Поддерживаемые операции
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Supported operations
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is_constructible
is_trivially_constructible
is_nothrow_constructible		(C++11)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible		(C++11)
(C++11)
(C++11)
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible		(C++11)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible		(C++11)
(C++11)
(C++11)
is_assignable
is_trivially_assignable
is_nothrow_assignable		(C++11)
(C++11)
(C++11)
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable		(C++11)
(C++11)
(C++11)
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable		(C++11)
(C++11)
(C++11)
is_destructible
is_trivially_destructible
is_nothrow_destructible		(C++11)
(C++11)
(C++11)
has_virtual_destructor(C++11)
Отношения собственности и запросов
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Relationships and property queries
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is_same(C++11)
is_base_of(C++11)
is_convertible(C++11)
alignment_of(C++11)
rank(C++11)
extent(C++11)
Тип модификаций
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Type modifications
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remove_cv
remove_const
remove_volatile		(C++11)
(C++11)
(C++11)
add_cv
add_const
add_volatile		(C++11)
(C++11)
(C++11)
make_signed(C++11)
make_unsigned(C++11)
Тип преобразования
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Type transformations
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aligned_storage(C++11)
aligned_union(C++11)
decay(C++11)
enable_if(C++11)
conditional(C++11)
common_type(C++11)
underlying_type(C++11)
result_of(C++11)
Введите черта констант
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Type trait constants
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integral_constant(C++11)
 
Заголовочный файл <type_traits>
template< std::size_t Len, std::size_t Align = /*default-alignment*/ >
struct aligned_storage;
 (начиная с C++11)
Обеспечивает член ЬурейеЕ type, что POD тип подходит для использования в качестве неинициализированные для хранения любой объект, размер которого не превышает Len и, выравнивание требованием является делителем Align. Значение по умолчанию Align является наиболее строгим (самый большой) требование выравнивания для любого объекта, размер которого не превышает Len.
Original:
Provides the member typedef type, which is a POD type suitable for use as uninitialized storage for any object whose size is at most Len and whose alignment requirement is a divisor of Align. The default value of Align is the most stringent (the largest) alignment requirement for any object whose size is at most Len.
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Содержание

[править] Член типов

Имя
Original:
Name
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 Definition
type
POD тип размера Len с выравниванием Align требования
Original:
the POD type of size Len with alignment requirement Align
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[править] Notes

Тип определяется std::aligned_storage может быть использован для создания неинициализированных блоков памяти подходят для хранения объектов данного типа, необязательно соответствие строгим, чем это необходимо, например, в кэш или границы страницы.
Original:
The type defined by std::aligned_storage can be used to create uninitialized memory blocks suitable to hold the objects of given type, optionally aligned stricter than necessary, for example on a cache or page boundary.
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[править] Возможная реализация

Кроме аргумент по умолчанию, aligned_storage выражается в терминах alignas
Original:
Except for default argument, aligned_storage is expressible in terms of alignas:
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template<std::size_t Len, std::size_t Align>
struct aligned_storage {
    typedef struct {
        alignas(Align) unsigned char data[Len];
    } type;
};

[править] Пример

Примитивных статический класс вектор, демонстрируя создания, доступа и уничтожения объектов в соответствие хранения
Original:
A primitive static vector class, demonstrating creation, access, and destruction of objects in aligned storage
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#include <iostream>
#include <type_traits>
#include <string>
 
template<class T, std::size_t N>
class static_vector
{
    // propertly aligned uninitialized storage for N T's
    typename std::aligned_storage <sizeof(T), std::alignment_of<T>::value>::type data[N];
    std::size_t m_size;
public:
 
    static_vector() : m_size(0) {};
    // Create an object in aligned storage
    template<typename ...Args> void emplace_back(Args&&... args)
    {
        new(data+m_size) T(std::forward<Args>(args)...);
        m_size++; // bounds check omitted
    }
 
    // Access an object in aligned storage
    const T& operator[](size_t pos) const
    {
        return reinterpret_cast<const T&>(data[pos]);
    }
    // Delete objects from aligned storage
    ~static_vector()
    {
        for(std::size_t pos = 0; pos < m_size; ++pos) {
            reinterpret_cast<const T*>(data+pos)->~T();
        }
    }
};
 
int main()
{
    static_vector<std::string, 10> v1;
    v1.emplace_back(std::string(5, '*'));
    v1.emplace_back(std::string(10, '*'));
    std::cout << v1[0] << '\n' << v1[1] << '\n';
}

Вывод: 

*****
**********

[править] См. также

alignas спецификатор
указывает, что для хранения переменной должны быть согласованы конкретные (C++11) сумму
Original:
specifies that the storage for the variable should be aligned by specific amount (C++11)
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[edit]
(C++11)
получает выравнивания типа требований
Original:
obtains the type's alignment requirements
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(шаблон класса) [edit]
(C++11)
определяет тип подходит для использования в качестве неинициализированные для хранения всех данных типов
Original:
defines the type suitable for use as uninitialized storage for all given types
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(шаблон класса) [edit]
(C++11)
POD типа с требованием выравнивания так велика, как любой другой тип скаляра
Original:
POD type with alignment requirement as great as any other scalar type
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(определение типа) [edit]
Источник — «http://ru.cppreference.com/mwiki/index.php?title=cpp/types/aligned_storage&oldid=31396»