Defined in header <type_traits> | ||
---|---|---|
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.
Name | Definition |
---|---|
type | the trivial type suitable for storage of any type from Types |
template< std::size_t Len, class... Types > using aligned_union_t = typename aligned_union<Len,Types...>::type; | (since C++14) |
alignment_value
[static] | the strictest alignment requirement of all Types (public static member constant) |
#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)...})]; }; }; |
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 |
(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) |
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