3 ms·

This is not a problem that C or C++ programmers actually encounter, ever.

• ncruces 6mo ago
  I actually encountered it a couple weeks ago. Can you spot the infinite loop in this function? char* strcpy(char* restrict d, const char* restrict s) { stpcpy(d, s); return d; } I'll help. A call to `stpcpy` that ignores the return value can be swapped with a call to the (more likely to be optimized) `strcpy`. Since that's infinite recursion, and there is no forward progress, it's undefined behavior and anything goes. This isn't just theory, it actually broke things in practice for me.
  • rssoconnor 6mo ago
    Naming an externally linked function with the prefix "str" is by itself UB since that prefix is reserved for <string.h>.
    • ncruces 6mo ago
      Right. I am doing a standard library replacement, and forgot I needed to compile freestanding. Oops. My bad. So `str` and `mem` are reserved. But then so are `to` and `is` (by <ctype.h>). Just forget about having a function named `is_valid_user`. And so are `mtx_`, `cnd_`, `thrd_`, `atomic_`, `memory_`... Which is why... everything in C is UB.