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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;
 (C++11およびそれ以降)
サイズは最もtypeとした、アラインメント要件Lenの除数である任意のオブジェクトの初期化されていないストレージとして使用するのに適したPOD型であるメンバのtypedefAlignは、用意されています。 Alignのデフォルト値は、ほとんどのサイズLenにある任意のオブジェクトの（最大）の最も厳しいアラインメント要件です.
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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目次

[編集] メンバータイプ

名前
Original:
Name
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 Definition
type
アライメント要件LenでサイズAlignのPOD型
Original:
the POD type of size Len with alignment requirement Align
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[編集] ノート

std::aligned_storageによって定義された型は、キャッシュやページ境界上例えば、必要に応じて、必要以上に厳格に整列、与えられた型のオブジェクトを保持するのに適した初期化されていないメモリブロックを作成するために使用することができます.
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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[編集] 可能な実装

デフォルトの引数を除き、aligned_storageはalignasの面で表現できる
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;
};

[編集] 例

プリミティブstatic vectorクラス、デモの作成、アクセス、および整列ストレージ内のオブジェクトの破壊
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: 

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

[編集] も参照してください

alignas指定子
変数の記憶領域が特定の量(C++11)で整列されるように指定します
Original:
specifies that the storage for the variable should be aligned by specific amount (C++11)
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[edit]
(C++11)
型の整列要求を取得します
Original:
obtains the type's alignment requirements
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(クラステンプレート) [edit]
(C++11)
指定されたすべてのタイプのための初期化されていないストレージとして使用するのに適したタイプを定義します
Original:
defines the type suitable for use as uninitialized storage for all given types
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(クラステンプレート) [edit]
(C++11)
他のスカラー型として素晴らしいとアラインメント要件とPOD型
Original:
POD type with alignment requirement as great as any other scalar type
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(typedef) [edit]
「http://ja.cppreference.com/mwiki/index.php?title=cpp/types/aligned_storage&oldid=28180」から取得