efficient comparator for an std::map with a struct key

Question

I have a struct of following type which I am planning use as a key in a map. Hence I write a comparator like below. I would like to know if there is a more elegant yet efficient way of doing this.
May be using std::pair or something.

struct T 
{
  int a, b, c, d;

  bool operator< (const T& r) {
    if (a < r.a)
       return true
    else if (a == r.a)
       if (b < r.b)
          return true;
       else if (b == r.b)
            if (c < r.c) 
                return true;
            else if (c == r.c)
                if (d < r.d)
                   return true;
    return false;
  }
}

Answer 1

Can you use C++11? If so:

struct T {
    int a, b, c, d;

    bool operator<(const T& rhs) const {
        return tied() < rhs.tied();
    }

private:
    std::tuple<int, int, int, int> tied() const {
        return std::make_tuple(a, b, c, d);
    }
};

Alternatively, I would prefer returning at each possible opportunity to avoid the error-prone awkward nesting approach:

bool operator<(const T& rhs) const {
    if (a != rhs.a) return a < rhs.a;
    if (b != rhs.b) return b < rhs.b;
    if (c != rhs.c) return c < rhs.c;
    return d < rhs.d;
}