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{{cpp/title|aligned_storage}}
{{cpp/meta/navbar}}
{{dcl begin}}
{{dcl header|type_traits}}
{{dcl|since=c++11|deprecated=c++23|1=
template< std::size_t Len, std::size_t Align = /* default-alignment */ >
struct aligned_storage;
}}
{{dcl end}}

Provides the nested type ''{{tt|type}}'', which satisfies {{named req|TrivialType}} and {{named req|StandardLayoutType}} and suitable for use as uninitialized storage for any object whose size is at most {{tt|Len}} and whose [[cpp/language/object#Alignment|alignment requirement]] is a divisor of {{tt|Align}}.

The default value of {{tt|Align}} is the most stringent (the largest) alignment requirement for any object whose size is at most {{tt|Len}}. If the default value is not used, {{tt|Align}} must be the value of {{c|alignof(T)}} for some type {{tt|T}}, or the behavior is undefined.

The behavior is undefined if {{c|1=Len == 0}}.

It is implementation-defined whether any [[cpp/language/object#Alignment|extended alignment]] is supported.

{{cpp/types/nospec}}

===Member types===
{{dsc begin}}
{{dsc hitem|Name|Definition}}
{{dsc|{{tt|type}}|a [[cpp/named req/TrivialType|trivial]] and [[cpp/named req/StandardLayoutType|standard-layout]] type of at least size {{tt|Len}} with alignment requirement {{tt|Align}}}}
{{dsc end}}

===Helper types===
{{dcl begin}}
{{dcl|since=c++14|deprecated=c++23|1=
template< std::size_t Len, std::size_t Align = /* default-alignment */ >
using aligned_storage_t = typename aligned_storage<Len, Align>::type;
}}
{{dcl end}}

===Notes===
The type defined by {{tt|std::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 using [[cpp/language/new|placement new]] and destroyed with explicit destructor calls.

===Possible implementation===
Except for default argument, aligned_storage is expressible in terms of alignas:
{{eq fun
|1=
template<std::size_t Len, std::size_t Align = /* default alignment not implemented */>
struct aligned_storage
{
    struct type
    {
        alignas(Align) unsigned char data[Len];
    };
};
}}

===Example===
{{example
|A primitive static vector class, demonstrating creation, access, and destruction of objects in aligned storage.
|code=
#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 storage
    template<typename ...Args> void emplace_back(Args&&... args)
    {
        if (m_size >= N) // Possible error handling
            throw std::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 storage
    const T& operator[](std::size_t pos) const
    {
        // Note: std::launder is needed after the change of object model in P0137R1
        return *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 P0137R1
            std::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';
}
|output=
*****
**********
}}

===See also===
{{dsc begin}}
{{dsc inc|cpp/language/dsc alignas}}
{{dsc inc|cpp/types/dsc alignment_of}}
{{dsc inc|cpp/memory/c/dsc aligned_alloc}}
{{dsc inc|cpp/types/dsc aligned_union}}
{{dsc inc|cpp/types/dsc max_align_t}}
{{dsc inc|cpp/utility/dsc launder}}
{{dsc end}}

{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

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