Reading a csv file and storing the data in an array using C++ in Visual Studio Code

Question

I have a csv file called "input.csv" (UTF-8, no CR, LF only). It looks like

it has 51 rows and 3 columns. I have to read the csv file and perform some mathematical operations on the data. I have tried couple of codes to read the csv file in c++ but none of them seem to work. I tried these link

I am using these codes and changing the file name but I am not getting any outputs. I cannot seem to figure out the problem. currently I am using this code taken from second link

#include <iterator>
#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <string>

class CSVRow
{
    public:
        std::string_view operator[](std::size_t index) const
        {
            return std::string_view(&m_line[m_data[index] + 1], m_data[index + 1] -  (m_data[index] + 1));
        }
        std::size_t size() const
        {
            return m_data.size() - 1;
        }
        void readNextRow(std::istream& str)
        {
            std::getline(str, m_line);

            m_data.clear();
            m_data.emplace_back(-1);
            std::string::size_type pos = 0;
            while((pos = m_line.find(',', pos)) != std::string::npos)
            {
                m_data.emplace_back(pos);
                ++pos;
            }
            // This checks for a trailing comma with no data after it.
            pos   = m_line.size();
            m_data.emplace_back(pos);
        }
    private:
        std::string         m_line;
        std::vector<int>    m_data;
};

std::istream& operator>>(std::istream& str, CSVRow& data)
{
    data.readNextRow(str);
    return str;
}   
int main()
{
    std::ifstream       file("input.csv");

    CSVRow              row;
    while(file >> row)
    {
        std::cout << "4th Element(" << row[3] << ")\n";
    }
}

Does anyone knows where is the problem?

When you step through the program with the debugger (and set it up in VS Code if you haven't already. Using a debugger to help you debug can save you insane amounts of time) Is input.csv successfully opened? — user4581301
– user4581301, Commented Jul 26, 2021 at 22:06
m_data.emplace_back(pos); appears to be strong the location of the comma, not the value found between the commas. — user4581301
– user4581301, Commented Jul 26, 2021 at 22:22

user4581301 · Accepted Answer · 2021-07-26 22:40:38Z

The first issue is that you are reading floating point numbers into integer vector, so that is going to lose information.

    // std::vector<int>    m_data;   // Don't need this if you know
                                     // there is always three values.
    // std::string         m_line;   // Don't need this.

    // Have a member for each column
    double col1;
    double col2;
    double col3;

Your second issue is that the code above is used to parse strings. You need to convert that into reading floating point numbers.

    void readNextRow(std::istream& str)
    {
        std::string line;
        std::getline(str, line);

        std::stringstream linestream(line);
        char comma1;
        char comma2;
        bool ok = false;

        if (linestream >> col1 >> comma1 >> col2 >> comma2 >> col3) {
            // Read worked.
            if (comma1 == ',' && comma2 == ',') {
               // There were commas
               ok = true;
            }
        }
      
        if (!ok) {
            str.setstate(std::ios::failbit);
        }
    }

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