Below is my code that 1) writes a CSV file with three columns of integer data (plus column names on the first line) and 2) reads the CSV file. I'm new to C++ and would appreciate some code review.
Also, I'm bothered by the fact that my technique requires all of the data to be integers. I'd appreciate advice on how I could generalize this code to write/read data with a mix of integers, doubles, strings, etc.
#include <string> // std::string
#include <fstream> // std::ofstream, std::ifstream
#include <vector> // std::vector
#include <utility> // std::pair
#include <stdexcept> // std::runtime_error
#include <sstream> // std::stringstream
#include <iostream> // std::cout, std::cin
void write_csv(std::string filename, std::vector<std::pair<std::string, std::vector<int>>> dataset){
// Make a CSV file with one or more columns of integer values
// Each column of data is represented by the pair <column name, column data>
// as std::pair<std::string, std::vector<int>>
// The dataset is represented as a vector of these columns
// Note that all columns should be the same size
// Create an output filestream object
std::ofstream myFile(filename);
// Send column names to the stream
for(int j = 0; j < dataset.size(); ++j)
{
myFile << dataset.at(j).first;
if(j != dataset.size() - 1) myFile << ","; // No comma at end of line
}
myFile << "\n";
// Send data to the stream
for(int i = 0; i < dataset.at(0).second.size(); ++i)
{
for(int j = 0; j < dataset.size(); ++j)
{
myFile << dataset.at(j).second.at(i);
if(j != dataset.size() - 1) myFile << ","; // No comma at end of line
}
myFile << "\n";
}
// Close the file
myFile.close();
}
std::vector<std::pair<std::string, std::vector<int>>> read_csv(std::string filename){
// Reads a CSV file into a vector of <string, vector<int>> pairs where
// each pair represents <column name, column values>
// Create a vector of <string, int vector> pairs to store the result
std::vector<std::pair<std::string, std::vector<int>>> result;
// Create an input filestream
std::ifstream myFile(filename);
// Make sure the file is open
if(!myFile.is_open()) throw std::runtime_error("Could not open file");
// Helper vars
std::string line, colname;
int val;
// Read the column names
if(myFile.good())
{
// Extract the first line in the file
std::getline(myFile, line);
// Create a stringstream from line
std::stringstream ss(line);
// Extract each column name
while(std::getline(ss, colname, ',')){
// Initialize and add <colname, int vector> pairs to result
result.push_back({colname, std::vector<int> {}});
}
}
// Read data, line by line
while(std::getline(myFile, line))
{
// Create a stringstream of the current line
std::stringstream ss(line);
// Keep track of the current column index
int colIdx = 0;
// Extract each integer
while(ss >> val){
// Add the current integer to the 'colIdx' column's values vector
result.at(colIdx).second.push_back(val);
// If the next token is a comma, ignore it and move on
if(ss.peek() == ',') ss.ignore();
// Increment the column index
colIdx++;
}
}
// Close file
myFile.close();
return result;
}
int main() {
// // Make three vectors, each of length N filled with 1s, 2s, and 3s
int N = 1000;
std::vector<int> vec1(N, 1);
std::vector<int> vec2(N, 2);
std::vector<int> vec3(N, 3);
// Wrap into a vector
std::vector<std::pair<std::string, std::vector<int>>> vals = {{"One", vec1}, {"Two", vec2}, {"Three", vec3}};
// Write the vector to CSV
write_csv("three_cols.csv", vals);
// Read three_cols.csv
std::vector<std::pair<std::string, std::vector<int>>> three_cols = read_csv("three_cols.csv");
// Print row and column counts to check if this was successful
std::cout << "Rows: " << three_cols.at(0).second.size() << ", Columns: " << three_cols.size() << std::endl;
return 0;
}
