How to read data from a csv file in C++ ?

In this article we will discuss and create a class to read data from a CSV File.

What is a CSV File ?

A csv file is a kind of flat file used to store the data. In this each row contains data separated by comma.
For example,

20,hi,99
3,4,5
a,b,c
3,4,1

Creating a Class CSVReader to read Data from CSV File

Let’s create a class CSVReader that provides API to read data from a CSV File

/*
 * A class to read data from a csv file.
 */
class CSVReader
{
	std::string fileName;
	std::string delimeter;

public:
	CSVReader(std::string filename, std::string delm = ",") :
			fileName(filename), delimeter(delm)
	{ }

	// Function to fetch data from a CSV File
	std::vector<std::vector<std::string> > getData();
};

It accepts the filename as constructor argument and provides a member function that reads the content of CSV file and returns the data in a vector of vector<std::string> i.e.

// Function to fetch data from a CSV File
std::vector<std::vector<std::string> > getData();

All comma separated elements in a single row will be stored in vector of strings i.e.

std::vector<std::string>

Now Data of each row i.e. vector<string> will be stored in another vector i.e.

std::vector<std::vector<std::string> >

This member function will parse the content of csv file line by line and store data in vector< vector <string> > i.e.

/*
* Parses through csv file line by line and returns the data
* in vector of vector of strings.
*/
std::vector<std::vector<std::string> > CSVReader::getData()
{
	std::ifstream file(fileName);

	std::vector<std::vector<std::string> > dataList;

	std::string line = "";
	// Iterate through each line and split the content using delimeter
	while (getline(file, line))
	{
		std::vector<std::string> vec;
		boost::algorithm::split(vec, line, boost::is_any_of(delimeter));
		dataList.push_back(vec);
	}
	// Close the File
	file.close();

	return dataList;
}

Let’s create an object of class CSVReader class and read the data from csv file i.e.

// Creating an object of CSVWriter
CSVReader reader("example.csv");

// Get the data from CSV File
std::vector<std::vector<std::string> > dataList = reader.getData();

Complete example is as follows,

#include <iostream>
#include <fstream>
#include <vector>
#include <iterator>
#include <string>
#include <algorithm>
#include <boost/algorithm/string.hpp>

/*
 * A class to read data from a csv file.
 */
class CSVReader
{
	std::string fileName;
	std::string delimeter;

public:
	CSVReader(std::string filename, std::string delm = ",") :
			fileName(filename), delimeter(delm)
	{ }

	// Function to fetch data from a CSV File
	std::vector<std::vector<std::string> > getData();
};

/*
* Parses through csv file line by line and returns the data
* in vector of vector of strings.
*/
std::vector<std::vector<std::string> > CSVReader::getData()
{
	std::ifstream file(fileName);

	std::vector<std::vector<std::string> > dataList;

	std::string line = "";
	// Iterate through each line and split the content using delimeter
	while (getline(file, line))
	{
		std::vector<std::string> vec;
		boost::algorithm::split(vec, line, boost::is_any_of(delimeter));
		dataList.push_back(vec);
	}
	// Close the File
	file.close();

	return dataList;
}
int main()
{
	// Creating an object of CSVWriter
	CSVReader reader("example.csv");

	// Get the data from CSV File
	std::vector<std::vector<std::string> > dataList = reader.getData();

	// Print the content of row by row on screen
	for(std::vector<std::string> vec : dataList)
	{
		for(std::string data : vec)
		{
			std::cout<<data << " , ";
		}
		std::cout<<std::endl;
	}
	return 0;

}

Output:

20 , hi , 99 , 
3 , 4 , 5 , 
a , b , c , 
3 , 4 , 1 ,

To Compile the above code use following command in Linux,

g++ –std=c++11 example.cpp