How to write data in a CSV file in C++
In this article we will discuss, how to create a class to write data to 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,
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20,hi,99 3,4,5 a,b,c 3,4,1 |
Creating a CSVWriter Class to store Data to CSV File
Let’s create a class CSVWriter that provides API to store data to CSV File
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/* * A class to create and write data in a csv file. */ class CSVWriter { std::string fileName; std::string delimeter; int linesCount; public: CSVWriter(std::string filename, std::string delm = ",") : fileName(filename), delimeter(delm), linesCount(0) {} /* * Member function to store a range as comma seperated value */ template<typename T> void addDatainRow(T first, T last); }; |
Its constructor accepts the filename as an argument. It also provide a template member function that accepts a range as an argument and store all of them in last row, separated by comma i.e.
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/* * This Function accepts a range and appends all the elements in the range * to the last row, seperated by delimeter (Default is comma) */ template<typename T> void CSVWriter::addDatainRow(T first, T last) { std::fstream file; // Open the file in truncate mode if first line else in Append Mode file.open(fileName, std::ios::out | (linesCount ? std::ios::app : std::ios::trunc)); // Iterate over the range and add each lement to file seperated by delimeter. for (; first != last; ) { file << *first; if (++first != last) file << delimeter; } file << "\n"; linesCount++; // Close the file file.close(); } |
As this function expects a range, we can pass iterator of any container like vector/set or an array.
Let’s create an object of CSVWriter class i.e.
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// Creating an object of CSVWriter CSVWriter writer("example.csv"); |
Write a Vector of strings to CSV file using CSVWriter class
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// Creating a vector of strings std::vector<std::string> dataList_1 = { "20", "hi", "99" }; // Adding vector to CSV File writer.addDatainRow(dataList_1.begin(), dataList_1.end()); |
Write a Set to CSV file using CSVWriter class
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// Create a set of integers std::set<int> dataList_2 = { 3, 4, 5}; // Adding Set to CSV File writer.addDatainRow(dataList_2.begin(), dataList_2.end()); |
Write an Array to CSV file using CSVWriter class
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// An array of int int arr [] = {3,4,1}; // Wrote an elements in array to csv file. writer.addDatainRow(arr , arr + sizeof(arr) / sizeof(int)); |
Check complete example as follows,
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#include <iostream> #include <fstream> #include <vector> #include <set> #include <iterator> #include <string> #include <algorithm> /* * A class to create and write data in a csv file. */ class CSVWriter { std::string fileName; std::string delimeter; int linesCount; public: CSVWriter(std::string filename, std::string delm = ",") : fileName(filename), delimeter(delm), linesCount(0) {} /* * Member function to store a range as comma seperated value */ template<typename T> void addDatainRow(T first, T last); }; /* * This Function accepts a range and appends all the elements in the range * to the last row, seperated by delimeter (Default is comma) */ template<typename T> void CSVWriter::addDatainRow(T first, T last) { std::fstream file; // Open the file in truncate mode if first line else in Append Mode file.open(fileName, std::ios::out | (linesCount ? std::ios::app : std::ios::trunc)); // Iterate over the range and add each lement to file seperated by delimeter. for (; first != last; ) { file << *first; if (++first != last) file << delimeter; } file << "\n"; linesCount++; // Close the file file.close(); } int main() { // Creating an object of CSVWriter CSVWriter writer("example.csv"); std::vector<std::string> dataList_1 = { "20", "hi", "99" }; // Adding vector to CSV File writer.addDatainRow(dataList_1.begin(), dataList_1.end()); // Create a set of integers std::set<int> dataList_2 = { 3, 4, 5}; // Adding Set to CSV File writer.addDatainRow(dataList_2.begin(), dataList_2.end()); std::string str = "abc"; // Adding characters in a string in csv file. writer.addDatainRow(str.begin(), str.end()); // An array of int int arr [] = {3,4,1}; // Wrote an elements in array to csv file. writer.addDatainRow(arr , arr + sizeof(arr) / sizeof(int)); return 0; } |
It generates a file example.csv with following contents,
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20,hi,99 3,4,5 a,b,c 3,4,1 |
To compile the above code on Linux, use following command,
g++ –std=c++11 example.cpp
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