It's simple: "string" literals in C++ are pointers to characters. std::vector has a constructor which takes a begin and end iterator and creates a vector with c

It's simple: "string" literals in C++ are pointers to characters. std::vector has a constructor which takes a begin and end iterator and creates a vector with contents copied from that range. Pointers are iterators in C++, and chars are implicitly convertible to ints, so overload resolution selects the aforementioned constructor. The pointer to "1" and the pointer to "2" don't point into the same object, so trying to iterate from one to the other eventually causes a dereference past the end of "1" which is undefined behavior.