std::aligned_union

template< std::size_t Len, class... Types >
struct aligned_union;

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

Helper types

template< std::size_t Len, class... Types >
using aligned_union_t = typename aligned_union<Len,Types...>::type;

Member constants

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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also