Read a text file,C++

Question

I wanted to read this text file which has 6 columns. The problem is in the second column the input is in form of class interval and I don't know how to read that,the last I tried isn't doing the job. Moreover I wanted to print the second column and third but it's doing something else. Any help please.

#include <iostream>
#include <cmath>
#include <fstream>
#include <sstream>
int main()
{

    std::ifstream f("t2kflux.txt");
    std::string line;
    while (std::getline(f, line))
    {
        float serial;
        double Energy, Energy2;
        double mu;
        double mubar;
        double e;
        double ebar;
        std::istringstream ss(line);
        ss >> serial >> Energy >> Energy2 >> mu >> mubar >> e >> ebar;
        std::cout << Energy << "\t" << mu << "\n";
    }
}

The data sample is

                        Flux (/cm^2/1E21p.o.t/50MeV)
Bin#    Energy (GeV)    numu            anti-numu       nue             anti-nue
---------------------------------------------------------------------------------
1        0.00- 0.05     1.27e+04        1.64e+04        1.80e+02        2.97e+01
2        0.05- 0.10     5.40e+04        5.41e+04        1.02e+03        1.23e+02
3        0.10- 0.15     1.11e+05        3.98e+04        2.17e+03        2.12e+02
4        0.15- 0.20     1.75e+05        3.10e+04        3.23e+03        2.86e+02
5        0.20- 0.25     2.62e+05        2.78e+04        4.08e+03        3.56e+02
6        0.25- 0.30     3.68e+05        2.77e+04        4.73e+03        4.15e+02
7        0.30- 0.35     4.83e+05        2.83e+04        5.27e+03        4.61e+02
8        0.35- 0.40     5.97e+05        2.92e+04        5.58e+03        4.93e+02
9        0.40- 0.45     7.21e+05        2.97e+04        5.80e+03        5.18e+02
10       0.45- 0.50     8.89e+05        2.93e+04        5.77e+03        5.31e+02
11       0.50- 0.55     1.11e+06        2.93e+04        5.72e+03        5.35e+02
12       0.55- 0.60     1.24e+06        2.98e+04        5.53e+03        5.31e+02
13       0.60- 0.65     1.23e+06        2.92e+04        5.33e+03        5.26e+02
14       0.65- 0.70     1.14e+06        2.80e+04        5.03e+03        5.15e+02
15       0.70- 0.75     9.10e+05        2.59e+04        4.76e+03        5.05e+02

Answer 1

From what I understand of what you are trying to do I think you have two problems.

The first is you are reading the first three lines as if they were data but they are not, they are header information. So I think you need to just skip past the first three lines:

// Skip first three lines
std::getline(f, line);
std::getline(f, line);
std::getline(f, line);

The other is you need to read the dash '-' character between your class interval values.

So all in all something like this:

#include <iostream>
#include <cmath>
#include <fstream>
#include <sstream>

int main()
{

    std::ifstream f("t2kflux.txt");
    std::string line;

    // Skip first three lines
    std::getline(f, line);
    std::getline(f, line);
    std::getline(f, line);

    while(std::getline(f, line))
    {
        float serial;
        double Energy, Energy2;
        double mu;
        double mubar;
        double e;
        double ebar;

        char dash; // to absorb the '-' separator

        std::istringstream ss(line);

        ss >> serial >> Energy >> dash >> Energy2 >> mu >> mubar >> e >> ebar;

        std::cout << Energy << "\t" << mu << "\n";
    }
}

Answer 2

I have written the following code and it is working fine for me. I hope this may help you.

#include<iostream>
#include<cmath>
#include<fstream>
#include<string>
#include<sstream>
 int main()
{
std::ifstream f("honey.txt");
std::string line;
while(std::getline(f,line))
{
float serial;
std::string Energy,Energy2;
std::string mu;
std::string mubar;
std::string e;
std::string ebar;
std::istringstream ss(line);
ss>>serial>>Energy>>Energy2>>mu>>mubar>>e>>ebar;
std::cout<<Energy<<"\t"<<mu<<"\n";
}
}

Other approach to solve this problem is:

Step 1: First create a program that removes dash(-) from the file.

Step 2: Use your program(as in question) and it will work correctly.