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std::aligned_storage

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aligned_storage(C++11)
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Defined in header <type_traits>
template< std::size_t Len, std::size_t Align = /*default-alignment*/ >
struct aligned_storage;
(seit C++11)
Stellt das Mitglied typedef type, das ein POD-Typ für die Verwendung als Speicher für jeden initialisierten Objekt, dessen Größe höchstens Len und deren Ausrichtung Anforderung ist ein Teiler von Align ist. Der Standardwert von Align ist die höchste (die größte) Angleichung Voraussetzung für jedes Objekt, dessen Größe höchstens 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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Inhaltsverzeichnis

[Bearbeiten] Mitglied Typen

Name
Original:
Name
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Definition
type
Die POD-Typ der Größe Len mit Angleichung Voraussetzung Align
Original:
the POD type of size Len with alignment requirement Align
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[Bearbeiten] Notes

Der Typ von std::aligned_storage definiert verwendet werden, um initialisierte Speicherblöcke geeignet sind, die Objekte des gegebenen Typs zu halten, gegebenenfalls strenger als notwendig ausgerichtet sind, zum Beispiel auf einem Cache oder Seitenbegrenzung zu erzeugen .
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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[Bearbeiten] Mögliche Implementierung

Außer Standard-Argument ist aligned_storage ausdrückbar der 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;
};

[Bearbeiten] Beispiel

Eine primitive statische Vektor Klasse demonstriert Erstellung, Zugriff und Zerstörung von Objekten in ausgerichtete Lagerung
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:

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

[Bearbeiten] Siehe auch

alignas Spezifizierer
gibt an, dass der Speicher für die Variable durch bestimmte Menge (C++11) ausgerichtet werden soll
Original:
specifies that the storage for the variable should be aligned by specific amount (C++11)
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[edit]
Ruft den Type der Alignment-Anforderungen
Original:
obtains the type's alignment requirements
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(Klassen-Template) [edit]
definiert die Art geeignet zur Verwendung als Speicher für alle initialisierten gegebenen Typen
Original:
defines the type suitable for use as uninitialized storage for all given types
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(Klassen-Template) [edit]
POD-Typ mit Angleichung Voraussetzung so groß wie alle anderen skalaren Typ
Original:
POD type with alignment requirement as great as any other scalar type
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(typedef) [edit]