Comment by tialaramex

The C optimizer is not allowed to re-order, so, unless you've specifically used some implementation override you know exactly how C will lay out basic types.

Likewise packing isn't allowed by the standard, so you'd again only need to talk about packing if you want to.

This seems like a reasonable place to start. Like the way driving school teaches you a U-turn but not a J-turn. Is a J turn actually a thing you might need? Maybe, but it's definitely not where we should start.