> Is it even possible to have zero undefined behavior in languages that allow user-defined pointers? It kinda boils down to what exactly you mean by defined be

> Is it even possible to have zero undefined behavior in languages that allow user-defined pointers? It kinda boils down to what exactly you mean by defined behavior. A C programmer's take might be that you can run a conforming program in an emulated abstract machine and get defined results out of it. And then you can run the same thing on real hardware and expect to get the same result (modulo implementation defined behavior). This definition leaves some things out (e.g. performance, observable effects in the "real world") but it captures the computational semantics. Another programmer's take might be more akin to a portable assembler. In that case, you certainly could define reads and writes for arbitrary pointers, in the sense that they must cause corresponding (attempted) loads and stores at the machine level. However, the definition wouldn't be complete since it inevitably leaves much to the underlying implementation. Thus you could have "defined" C programs that show completely different behaviors depending on which implementation and hardware you used. It would be impossible to say what the program's output must be "in the abstract." For someone who just wants to output assembly, maybe that's fine. I'm not sure other people would be too satisfied with it. An out of bounds write could still blow up your program and be remotely exploitable; practically the same thing as undefined behavior, except that now your compiler is also barred from optimizing. There's quite a bit of tension between these two camps. Alternatively, you could fully define it at a great runtime cost and potential exclusion of real hardware implementations.