c++, 조건부 sort하기

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
 
class record{
private:
    string _class;
    int _score;
 
    bool read_class(istream &in){
        string str;
        if(!getline(in, str, ','))
            return false;
        _class = str.substr(6, string::npos);
        return true;
    }
    bool read_score(istream &in){
        string str;
        if(!getline(in, str, '\n'))
            return false;
        _score = atoi(str.c_str());
        return true;
    }
public:
    bool operator<(const record &rhs) const{
        return _class!=rhs._class?_class>rhs._class:_class=="A"?_score<rhs._score:_score>rhs._score;
    }
    bool operator>(const record &rhs) const{
        return rhs < *this;
    }
    istream &read_from(istream &in){
        return (read_class(in) && read_score(in)), in;
    }
    ostream &write_to(ostream &out) const{
        return (out << "class_" << _class << "," << _score << endl);
    }
};
 
istream &operator>>(istream &in, record &r){
    return r.read_from(in);
}
ostream &operator<<(ostream &out, const record &r){
    return r.write_to(out);
}
 
int main(void)
{
    vector<record> records;
 
    {
        ifstream in("./test.csv");
        record r;
        while(in >> r)
        {
            records.push_back(r);
        }
        in.close();
    }
 
    sort(records.begin(), records.end(), greater<record>());
 
    {
        ofstream out("./result.csv",ios::app);
        ostream_iterator<record> out_iter(out);
        copy(records.begin(), records.end(), out_iter);
        out.close();
    }
    return 0;
}