Provides the nested typetype, which satisfiesTrivialType andStandardLayoutType and suitable for use as uninitialized storage for any object whose size is at mostLen and whosealignment requirement is a divisor ofAlign.

The default value ofAlign is the most stringent (the largest) alignment requirement for any object whose size is at mostLen. If the default value is not used,Align must be the value ofalignof(T) for some typeT, or the behavior is undefined.

The behavior is undefined ifLen==0.

It is implementation-defined whether anyextended alignment is supported.

If the program adds specializations forstd::aligned_storage, the behavior is undefined.

[edit]Member types

[edit]Helper types

[edit]Notes

The type defined bystd::aligned_storage<>::type can be used to create uninitialized memory blocks suitable to hold the objects of given type, optionally aligned stricter than their natural alignment requirement, for example on a cache or page boundary.

As with any other uninitialized storage, the objects are created usingplacement new and destroyed with explicit destructor calls.

[edit]Possible implementation

Except for default argument, aligned_storage is expressible in terms of alignas:

template<std::size_t Len,std::size_t Align=/* default alignment not implemented */>struct aligned_storage{struct type{        alignas(Align)unsignedchar data[Len];};};

[edit]Example

#include <cstddef>#include <iostream>#include <new>#include <string>#include <type_traits> template<class T,std::size_t N>class static_vector{// Properly aligned uninitialized storage for N T's    std::aligned_storage_t<sizeof(T), alignof(T)> data[N];std::size_t m_size=0; public:// Create an object in aligned storagetemplate<typename ...Args>void emplace_back(Args&&...args){if(m_size>= N)// Possible error handlingthrowstd::bad_alloc{}; // Construct value in memory of aligned storage using inplace operator new::new(&data[m_size]) T(std::forward<Args>(args)...);++m_size;} // Access an object in aligned storageconst T& operator[](std::size_t pos)const{// Note: std::launder is needed after the change of object model in P0137R1return*std::launder(reinterpret_cast<const T*>(&data[pos]));} // Destroy objects from aligned storage    ~static_vector(){for(std::size_t pos=0; pos< m_size;++pos)// Note: std::launder is needed after the change of object model in P0137R1std::destroy_at(std::launder(reinterpret_cast<T*>(&data[pos])));}}; int main(){    static_vector<std::string,10> v1;    v1.emplace_back(5,'*');    v1.emplace_back(10,'*');std::cout<< v1[0]<<'\n'<< v1[1]<<'\n';}

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[edit]See also

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