问CSV文件未从buffor获取数据

EN

#include <iostream>
#include <string>
#include <fstream>
#include <math.h>
#include <stdio.h>

using namespace std;

 int main ()
{
int num = 0;

fstream file;

string file_name;

cout << "Input file name: ";
cin>>file_name;
file.open(file_name.c_str());

if (file.fail())
{
    cout << "Unable to open file - try again" << endl;
    main ();
} else
{

file << "VALUE" << "\t" << "1/x" << "\t" << "sqrt" << endl;


while (num < 200)
{
    file << num << "\t" << 1/num << "\t" << sqrt(num) << endl;
    num ++;
}

file.close();
return 0;
}
}