https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127898
--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> --- buffer.data[buffer.len++] = c; So there is no sequence point between the buffer.data and buffer.len in c. So the question becomes which one is evaluated first. Buffer.data depends on buffer.len due to the counted_by attribute too. So buffer.len could be incremented first or buffer.len could be accessed for buffer.data. So this in theory could be undefined code. Unless gcc makes it defined which access happens first.
