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std::aligned_storage

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Defined in header <type_traits>
template< std::size_t Len, std::size_t Align = /*default-alignment*/ >
struct aligned_storage;
(desde C++11)
Proporciona la type miembro typedef, que es un tipo POD adecuado para uso como almacenamiento sin inicializar para cualquier objeto cuyo tamaño es como máximo Len y cuya alineación requisito es un divisor de Align. El valor predeterminado de Align es el requisito de alineación más estricta (la más grande) para cualquier objeto cuyo tamaño es como máximo 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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Contenido

[editar] Tipos de miembros

Nombre
Original:
Name
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Definition
type
el tipo de POD Len tamaño con Align alineación requisito
Original:
the POD type of size Len with alignment requirement Align
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[editar] Notas

El tipo definido por std::aligned_storage se puede utilizar para crear bloques de memoria sin inicializar adecuados para mantener los objetos de tipo dado, opcionalmente alineados estrictas de lo necesario, por ejemplo en una memoria caché o límite de la página .
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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[editar] Posible implementación

A excepción de argumento por defecto, aligned_storage es expresable en términos de 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;
};

[editar] Ejemplo

Una clase primitiva vector estático, demostrando creación, el acceso y la destrucción de los objetos en el almacenamiento alineados
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';
}

Output:

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

[editar] Ver también

alignas especificador
especifica que el almacenamiento para la variable debe estar alineado por (C++11) cantidad específica
Original:
specifies that the storage for the variable should be aligned by specific amount (C++11)
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[edit]
obtiene requisitos del tipo de alineación
Original:
obtains the type's alignment requirements
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(clase de plantilla) [edit]
define el tipo adecuado para su uso como almacenamiento sin inicializar todos los tipos dados
Original:
defines the type suitable for use as uninitialized storage for all given types
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(clase de plantilla) [edit]
Tipo POD con el requisito de alineación tan grande como cualquier otro tipo escalar
Original:
POD type with alignment requirement as great as any other scalar type
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(typedef) [edit]