我应该如何在此类的地图中重载“<”？

Question

I have the class tranzitie and a map<int, map<tranzitie, int>> . How should I overload the < operator for tranzitie in order for the map to work properly? It contains two chars and one string. I tried, but find() would't work well, considering values equal even though they weren't (in my perspective).

class tranzitie{
public:
    char litera;
    char top;
    string newst;

    bool operator==(const tranzitie& x);
    tranzitie& operator=(const tranzitie& x);
    tranzitie (const tranzitie& x);
    tranzitie(){};
    inline bool operator< (const tranzitie& rhs) const;
};

Answer 1

Prefer implement operator< as a free function instead of a member function. If you need to access the private members inside the operator< function you should make the operator< function a friend. In your case it is not needed as the members of tranzitie are public.

The easiest pattern to memorize is probably this:

bool operator<(const tranzitie& lhs, const tranzitie& rhs) {
  if (lhs.litera < rhs.litera) return true;
  if (rhs.litera < lhs.litera) return false;
  if (lhs.top < rhs.top) return true;
  if (rhs.top < lhs.top) return false;
  return lhs.newst < rhs.newst;
}

The best pattern to memorize is probably this:

bool operator<(const tranzitie& lhs, const tranzitie& rhs) {
  return
    std::tie(lhs.litera, lhs.top, lhs.newst) <
    std::tie(rhs.litera, rhs.top, rhs.newst);
}

Answer 2

You should compare all your data members:

 bool operator< (const tranzitie& rhs) const {
     if( litera == rhs.litera ) {
        if( top == rhs.top ) {
            return newst < rhs.newst;
        }
        return top < rhs.top;
     }
     return litera < rhs.litera;
 }