Multi-key sort

multi-key-sort.cc

// Type definition
class Object {
public:
  int key1, key2, key3, key4;
};

// Comparator
bool comparator(const Object & lhs, const Object & rhs) {
  if (lhs.key1 == rhs.key1) {
    if (lhs.key2 == rhs.key2) {
      if (lhs.key3 == rhs.key3) {
        return lhs.key4 < rhs.key4;
      }
      return lhs.key3 < rhs.key3;
    }
    return lhs.key2 < rhs.key2;
  }
  return lhs.key1 < rhs.key1;
}

// Sort

vector<Object> objs;
// do something with objs
sort(objs.begin(), objs.end(), comparator);

多关键字排序，关键字次序：key1 > key2 > key3 > key4。