Re: Union C++ standard

David,


>>> In C, type-punning via unions is allowed (i.e., fully defined behaviour
>>
>> That is not true.  Writing into one member and then reading from
>> another member is undefined behavior.
>
> No, it is correct. It would be helpful if you looked at the full


You have misunderstood the C conformance model, which revolves around
the use of "shall" and "shall not", and the kind of section in which
they appear (e.g., Constraints). See:
http://c0x.shape-of-code.com/4..html


For a longer discussion see: http://knosof.co.uk/cbook/


> """
> 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"). This might be a
> trap representation.
> """
>
> These quotations are from C18 (draft N2346), which is the current C
> standard (until C23 is finalised). They have not changed since C99,


This footnote was added in response to this DR (so it must have come
after C99):
http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_283.htm

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