Example of UBSan enum error

undefined-enum

$ cat undefined.cc
#include <stdexcept>

enum Enum {
    A,
    B,
    C,
    Invalid
};

bool decode(int userInput, Enum& e) {
    e = static_cast<Enum>(userInput);
    return e < Invalid;
}

int main() {
    Enum e;
    decode(2, e); // true
    decode(10, e); // false
    // do something with e...
}
$ clang++ undefined.cc -fsanitize=undefined 
$ ./a.out 
undefined.cc:12:12: runtime error: load of value 10, which is not a valid value for type 'Enum'