Type punning through a union is explicitly defined to work in C99 and C11 (footnote 95 in C11):
> If the member used to read the contents of a union object is not the same as the member last used to store a value in the object, the appropriate part of the object representation of the value is reinterpreted as an object representation in the new type as described in 6.2.6 (a process sometimes called ‘‘type punning’’).
Please don't help spread the myth that compiler writers can break this idiom. That said, I use memcpy in my own code.
> If the member used to read the contents of a union object is not the same as the member last used to store a value in the object, the appropriate part of the object representation of the value is reinterpreted as an object representation in the new type as described in 6.2.6 (a process sometimes called ‘‘type punning’’).
Please don't help spread the myth that compiler writers can break this idiom. That said, I use memcpy in my own code.