std::aligned_union
From cppreference.com
| Defined in header <type_traits>
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| template< std::size_t Len, class... Types > struct aligned_union; |
(since C++11) | |
Provides the nested type type, which is a trivial standard-layout type of a size and alignment suitable for use as uninitialized storage for an object of any of the types listed in Types. The size of the storage is at least Len. std::aligned_union also determines the strictest (largest) alignment requirement among all Types and makes it available as the constant alignment_value.
If sizeof...(Types) == 0 or if any of the types in Types is not a complete object type, the behavior is undefined.
It is implementation-defined whether any extended alignment is supported.
Member types
| Name | Definition |
type
|
the trivial type suitable for storage of any type from Types
|
Helper types
| template< std::size_t Len, class... Types > using aligned_union_t = typename aligned_union<Len,Types...>::type; |
(since C++14) | |
Member constants
| alignment_value [static] |
the strictest alignment requirement of all Types (public static member constant) |
Possible implementation
#include <algorithm> template <std::size_t Len, class... Types> struct aligned_union { static constexpr std::size_t alignment_value = std::max({alignof(Types)...}); struct type { alignas(alignment_value) char _s[std::max({Len, sizeof(Types)...})]; }; }; |
Example
| This section is incomplete Reason: no example |
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2979 | C++11 | complete type wasn't required | requires complete types |
See also
| (C++11) |
obtains the type's alignment requirements (class template) |
| (C++11) |
defines the type suitable for use as uninitialized storage for types of given size (class template) |