Your wording only works for "implementation defined", not "undefined". Both exist in the standard, and the former is quite sane to use. E.g., on any normal arch

Your wording only works for "implementation defined", not "undefined". Both exist in the standard, and the former is quite sane to use. E.g., on any normal architecture, specifying signed integer overflow to be implementation defined would have been great, though on e.g. the JS-style machine that abuses IEEE floats in limited range as integers, addition get's weird once the point floats to the left of where you'd normally write it by hand (in non-scientific notation). y = x; x += 1; x -= 1; true == (x != y); But I don't know of any actual integer machine that would want integer overflow to actually be UB.