In telephone inband signalling is, or rather, was to control circuit setup and teardown by tone signals within the speech band that is also transmitted from speaker to listener. Had the unfortunate effect that you use a specific whistle on the phone and lose the connection. Soon got exploited in more creative ways.
Anyway, in C++'s std::string often the same thing happens. When in C, you have a char*, and you can null it to mark the no value case. Not so in C++. You need a special value, and usually this is the empty string "". Fine and dandy as long as you can be sure that that value will never actually occur. Once this happens all the code will already be riddled with if (val != "") and you never find them all. Bad luck, just like with Y2K.
Neither do you have Maybe, the Haskell way of avoiding null pointer exceptions completely.