Well you only have guaranteed compatibility with C if a class is standard-layout, which requires that all members have the same access control (public, protecte

Well you only have guaranteed compatibility with C if a class is standard-layout, which requires that all members have the same access control (public, protected, private). So if there is any rule in C++ that mandates ordering within a "block" when there are multiple such "blocks", it's not for compatibility with C.