map对key排序

struct CmpByKeyLength 
{
  bool operator()(const string& k1, const string& k2) 
  {
    return k1.length() < k2.length();
  }
};

int main() 
{
  map<string, int, CmpByKeyLength> name_score_map;
  name_score_map["LiMin"] = 90; 
  name_score_map["ZiLinMi"] = 79; 
  name_score_map["BoB"] = 92; 
  name_score_map.insert(make_pair("Bing",99));
  name_score_map.insert(make_pair("Albert",86));
  for (map<string, int>::iterator iter = name_score_map.begin();
       iter != name_score_map.end();
       ++iter) 
  {
    cout << *iter << endl;
  }
  return 0;
}