[midjji]

There is absolutely undefined behaviour there. Undefined behaviour is defined not as nasal daemons but as: The compiler implementer does not guarantee that this behaviour will be hardware, circumstance, compiler version, or os consistent, nor that we will warn if we change this.

Packed is technically not a undefined behaviour, but it is certainly a trap. Especially because the compiler macros leads people to make defines which select packed by compiler automatically. Then the special case of didn't recognize compiler is just left empty, meaning compiles but no longer does what you think.

[fifjdynb]

You don't get to decide what UB means. It really does mean nasal demons are a possibility: all bets are off when you run that executable. Use of the term "undefined behaviour" to mean something else may be on the increase, unfortunately (https://mars.nasa.gov/technology/helicopter/status/298/what-...), but if we're talking about C, it's meaning is fixed.

[midjji]

I didnt, the deterministic nature of computer programs guarantees that what I wrote is the actual outcome.