std::aligned_storage

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C++
 
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aligned_storage(C++11)
aligned_union(C++11)
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Elemento definito nell'header <type_traits>
template<std::size_t Len, std::size_t Align =/*default-alignment*/>
struct aligned_storage;
(dal C++11)
Fornisce il type membro typedef, che è un tipo POD adatto all'uso come memoria non inizializzata per qualsiasi oggetto la cui dimensione è al massimo e Len cui allineamento requisito è un divisore di Align. Il valore predefinito di Align è il requisito più rigoroso allineamento (il più grande) per qualsiasi oggetto la cui dimensione è al massimo 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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Indice

[modifica]Membri tipi

Nome
Original:
Name
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 Definition
type
il tipo di POD Len dimensioni con Align allineamento requisito
Original:
the POD type of size Len with alignment requirement Align
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[modifica]Note

Tipo definito dal std::aligned_storage può essere usato per creare blocchi di memoria non inizializzate adatti a contenere gli oggetti di tipo determinato, eventualmente allineati rigorose del necessario, per esempio in una cache o limite di pagina.
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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[modifica]Possibile implementazione

Fatta eccezione per argomento di default, aligned_storage è esprimibile in termini di 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 {typedefstruct{ alignas(Align)unsignedchar data[Len];} type;};

[modifica]Esempio

Una classe primitiva vettore statico, dimostrando la creazione, l'accesso, e la distruzione di oggetti in memoria allineati
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'stypename 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 storagetemplate<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 storageconst T& operator[](size_t pos)const{returnreinterpret_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: 

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

[modifica]Vedi anche

alignas specificatore
specifica che il deposito per la variabile deve essere allineato (C++11) quantità specifica
Original:
specifies that the storage for the variable should be aligned by specific amount (C++11)
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[modifica]
(C++11)
ottiene requisiti di allineamento del tipo
Original:
obtains the type's alignment requirements
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(classe template)[modifica]
(C++11)
definisce il tipo adatto per l'uso come memoria non inizializzata per tutti i tipi di dati
Original:
defines the type suitable for use as uninitialized storage for all given types
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(classe template)[modifica]
(C++11)
Tipo di POD con il requisito di allineamento così grande come qualsiasi altro scalare
Original:
POD type with alignment requirement as great as any other scalar type
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(typedef)[modifica]
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