C++, 정렬할 때 메모리 문제

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>
using namespace std;
 
// class for sort
class sort_class
{
private:
string string1, string2;
//string string1, string2, string3, string4, string5, string6, string7, string8;
//string string9, string10, string11, string12, string13, string14, string15; 
public:
sort_class(const string& init_string1, const string& init_string2);
 
friend int Compare_By_string1(const sort_class& lhs, const sort_class& rhs);
//friend int Compare_By_string1234(const sort_class& lhs, const sort_class& rhs);
friend ostream& operator<<(ostream& os, const sort_class& obj)
{
	os<<obj.string1<<','<<obj.string2;
	return os;
}
};
 
sort_class::sort_class(const string& init_string1, const string& init_string2)
:string1(init_string1), string2(init_string2){}
 
// function that sorts by string1, 2개 열을 정렬
int Compare_By_string1(const sort_class& lhs, const sort_class& rhs)
{
	return (lhs.string1<rhs.string1);
}
 
// 4개 열을 정렬
/* 
int Compare_By_string1234(const sort_class& lhs, const sort_class& rhs)
{
	if(lhs.string1==rhs.string1)
	{
		if(lhs.string2==rhs.string2)
		{
			if(lhs.string3==rhs.string3)
			{
				return (lhs.string4<rhs.string4);
			}
			else if(lhs.string3!=rhs.string3)
			{
				return (lhs.string3<rhs.string3);
			}
		}
		else if(lhs.string2!=rhs.string2)
		{
			return (lhs.string2<rhs.string2);
		}
	}
	else if(lhs.string1!=rhs.string1)
	{
		return (lhs.string1<rhs.string1);
	}
}
*/
int main()
{
    // read 2001.csv file and put them into the test_vector
    ifstream file("2001.csv");
    vector<sort_class> test_vector;
 
    string string1, string2;
    while(getline(file, string1,',')
    &&getline(file,string2,'\n'))
    {
        test_vector.push_back(sort_class(string1,string2));
    }
    file.close();
 
    // sort the test_vector by string1
    sort(test_vector.begin(), test_vector.end(),Compare_By_string1);
 
    // write the sorted test_vector on out_2001.csv file
    ofstream fout("out_2001.csv");
    std::ostream_iterator<sort_class> output_iterator(fout,"\n");
    std::copy(test_vector.begin(),test_vector.end(),output_iterator);
    fout.close();
 
    return 0;
}