> it is false in the general case, since division by zero has a side effect in the form of invoking undefined behaviour.
They were careful to say “under the rules of C,” the rules define the behaviour of C. On the other hand, undefined behaviour is outside the rules, so I think they’re correct in what they’re saying.
The problem for me is that the compiler is not obliged to check that the code is following the rules. It puts so much extra weight on the shoulders of the programmer, though I appreciate that using only rules which can be checked by the compiler is hard too, especially back when C was standardised.
> They were careful to say "under the rules of C,"
Yes, and under the rules of C, division by zero has a side effect, namely invoking undefined behaviour.
> The problem for me is that the compiler is not obliged to check that the code is following the rules.
That part's actually fine (annoying, but ultimately a reasonable consequence of the "rules the compiler can check" issue); the real(ly bad and insidious) problem is that when the compiler does check that the code is following the rules, it's allowed to do it in deliberately backward way that uses any case of not following the rules as a excuse to break unrelated code.
Undefined behavior is not a side effect to be "invoked" by the rules of C. If UB happens, it means your program isn't valid. UB is not a side effect or any effect at all, it is the void left behind when the system of rules disappears.
They were careful to say “under the rules of C,” the rules define the behaviour of C. On the other hand, undefined behaviour is outside the rules, so I think they’re correct in what they’re saying.
The problem for me is that the compiler is not obliged to check that the code is following the rules. It puts so much extra weight on the shoulders of the programmer, though I appreciate that using only rules which can be checked by the compiler is hard too, especially back when C was standardised.