The problem with C and C++ isn't so much that undefined behavior exists, but the fact that the rules that determine when a program has defined behavior aren't f

The problem with C and C++ isn't so much that undefined behavior exists, but the fact that the rules that determine when a program has defined behavior aren't formalized rigorously enough. The C and C++ specifications are written in natural language, which always leaves room for ambiguity, no matter how pedantically one tries to write. If you want to convince a single other person that a C program you have written has no undefined behavior, then you and that person have to hopefully interpret English the same way. It would be completely hopeless to try to convince a hundred people that a nontrivial C program has no undefined behavior. And successful programs typically have way more than a hundred users.