exit() call inside a function which should return a reference

Question

In a library I have a function which searches for a key in a database and return a non-const reference to an object. I want to handle the case in which the key is not found,

Answer 1

The answer, as the other respondents, said, should be: throw an exception...

Type & get(const Key & k) {
     if( !my_db.key_exists(k) ) {
          std::stringstream error;
          error << "key " << k << " not found";
          throw std::runtime_error(error);
     }
     return my_db.at(k);
}