How to stream a comma separated txt file to a class object? - c++

Question

How do I stream a line of comma separated txt file to an object that contain first name, last name and age variables? I want to overload the >> operator to do such operations.
std::istream& operator>>(std::istream& file, PersonData& obj) {
std::string line, firstName, lastName, age;
while (std::getline(file, line)) {
std::stringstream ss(line);
std::getline(ss,firstName,',');
std::getline(ss,lastName,',');
std::getline(ss, age,',');
firstName >> obj.firstName;
lastName >> obj.lastName;
std::stoi(age) >> obj.age;
}
return file;
}

Answer 1

Your operator>> should read a single entry from the file.
If you have a class
struct Person {
std::string first_name;
std::string last_name;
unsigned age;
};
You can use in/output operators:
std::ostream& operator<<(std::ostream& out,const Person& p) {
out << p.first_name << ", " << p.last_name << ", " << p.age;
return out;
}
std::istream& operator>>(std::istream& in,Person& p){
const auto comma = ',';
std::getline(in,p.first_name,comma);
std::getline(in,p.last_name,comma);
std::string temp;
std::getline(in,temp);
p.age = std::stoi(temp);
return in;
}
And then extract one Person at a time from the file:
int main() {
std::stringstream ss{"Peter, Fish, 42\nLaura, Peterson, 105"};
Person p1,p2;
ss >> p1 >> p2;
std::cout << p1 << "\n" << p2;
};
Output:
Peter, Fish, 42
Laura, Peterson, 105
Live example
To read all entries from a file you can use a vector and a loop:
std::vector<Person> persons;
Person entry;
while(stream >> entry) persons.push_back(entry);
PS: I missed to remove leading blanks from the names. I'll leave that to you ;)

Answer 2

john-wick.txt
John,Wick,50
main.cpp
#include <iostream>
#include <fstream>
struct PersonData {
string firstname;
string lastname;
int age;
friend std::istream& operator>>(std::istream& in, PersonData& obj) {
char comma;
in >> obj.firstname >> comma >> obj.lastname >> comma >> obj.age;
return in;
}
}
int main(int argc, char *argv[]) {
std::ifstream file("john-wick.txt");
PersonData john;
file >> john;
}

Answer 3

Here's a stencil for your class:
class My_Class
{
public:
friend std::istream& operator>>(std::istream& input, My_Class& mc);
private:
// members go here.
};
std::istream& operator>>(std::istream& input, My_Class& mc)
{
// Insert code to read comma separated values here.
return input;
}
The above allows you to stream input to your class:
My_Class mc;
std::vector<My_Class> database;
while (input_file >> mc)
{
database.push_back(mc);
}
Edit 1: Reading CSV
Based on the code you posted, I believe this is what you want:
std::istream& operator>>(std::istream& input, My_Class& mc)
{
std::getline(input, mc.firstName,',');
std::getline(input, mc.lastName,',');
input >> mc.age;
// Ignore till the end of the line:
input.ignore(10000, '\n');
return input;
}
Editing your question with a sample of the input file will allow readers to confirm or deny the content of the function.