История изменений

6.5 Expressions:

7 An object shall have its stored value accessed only by an lvalue expression that has one of
the following types: 88)
— a type compatible with the effective type of the object,
— a qualified version of a type compatible with the effective type of the object,
— a type that is the signed or unsigned type corresponding to the effective type of the
object,
— a type that is the signed or unsigned type corresponding to a qualified version of the
effective type of the object,
— an aggregate or union type that includes one of the aforementioned types among its
members (including, recursively, a member of a subaggregate or contained union), or
— a character type.

Да, это UB. Можно использовать memcpy().

6.5 Expressions:

7 An object shall have its stored value accessed only by an lvalue expression that has one of
the following types: 88)
— a type compatible with the effective type of the object,
— a qualified version of a type compatible with the effective type of the object,
— a type that is the signed or unsigned type corresponding to the effective type of the
object,
— a type that is the signed or unsigned type corresponding to a qualified version of the
effective type of the object,
— an aggregate or union type that includes one of the aforementioned types among its
members (including, recursively, a member of a subaggregate or contained union), or
— a character type.