3 ms·

I would be afraid to do this with C++. My friend once sent me a snippet, maybe 10 lines of C+++, asking "can you spot the UB?". So I'm staring at these 10 lin

• tstenner 24d ago
  Was it the one with the elided null check?
  • aka-rider 24d ago
    I don't remember the details, roughly it was unexpected invocation of move semantic, causing use after free in a loop. My all-time favourite example is (again, my memory, I may be a bit wrong): for (int i = 0; i < (size_t)limit; ++i) { } at some point limit could potentially become greater than INT_MAX, the compiler decided that i<limit could never be true because that would cause signed int overflow which is UB, so it "optimized" the loop into while(true) signed unsigned mismatch makes me shiver
    • dgrunwald 24d ago
      The compiler cannot optimize that into `while(true)` because the original code does not encounter undefined behavior when `limit` is small enough to fit into `int`. What it can do: infer that `limit <= INT_MAX` and use that to optimize the code following after the loop (and in some cases, even the code before the loop).
      • aka-rider 24d ago
        This isn't complete example. I don't remember the details unfortunately. But somehow compiler has decided that i <= limit is always true.