File input and Output help

[Magi]

Hello all, I am having a really tough time figuring out how to structure the input of one .dat file and outputting into another one. I have to loop through a file structured "doe, john, 1500", check for errors and then increase the mp by 50. You also have to do this through using a person class too. I think I need to use a while loop to go to eof and use getline to input correctly, but im not sure how to structure it. Any help would be fantastic, I am pretty new to C++ and I feel like I am floundering on this one.

Data file:
Horowitz,Jake,1200.24
Flabitz,Bubba,1712.38
Blackwell,Sharon,1872.93
Molerat,Rufus,501.00
Goodall,Jane,1567.43
Sommerset,William,1359.57
Van Helsing,Marcus,1675.21
Welfirth,Bula,1903.83
Poling,Kerri,1243.32
Lee,Aswari Kalim,1839.42
Lisa,Mona,2409.48
Lisbon,Frieda,1543.70
Hatcher,Gary,1220.13

person class

#pragma once
#if !defined(person_included)
#define person_included
#include <string>
#include <iostream>


class person{
public:
    std::string first_name;
    std::string last_name;
    double monthly_pay;


    person():
    first_name ("john"),
    last_name ("doe"),
    monthly_pay (0)
    {}


person(const std::string& init_fn,
      const std::string& init_ln,
      float init_mp
     ):first_name(init_fn),
       last_name(init_ln),
       monthly_pay (init_mp)
    {}


    std::string get_first_name() const {return first_name;}
    std::string get_last_name() const {return last_name;}
    float get_monthly_pay() const {return monthly_pay+50.00;}


};
#endif

and then here is my main

#include <iostream>
#include <fstream>
#include <string>
#include "person class.h"


int main() {


std::ifstream input("person.dat");


if (!input) {
std::cerr << "cannot open file" << std::endl;
return 1;
}


person in;


input >> in.last_name;


if (input.eof()) {
std::cerr <<"no data in file" << std::endl;
return 2;
}


if (input.fail() || input.peek() != ',' || !input.ignore()) {
std::cerr <<"last name error" << std::endl;
return 3;
}


if (!getline(input, in.first_name, ',')) {
std::cerr <<"first name error" << std::endl;
return 4;
}


input >> in.monthly_pay;


if (!input) {
std::cerr <<"error with pay" << std::endl;
return 5;
}


std::ofstream stream ("output.dat");
stream << in.last_name <<"," << in.first_name << "," << in.monthly_pay << "/n"<<std::endl;
return
0;


}

[Aslaville]

Why not just structure your program into functions

std::istream read ( std::istream & in , person & data_belongs_to )
{
       if ( in )
    {
       //fix your series of if statements here
     }
   return in;
}

EDIT
Actually I don't understand why you concern yourself with whether it is the end of file or some other error, for the time being, you only need to know whether the input was successful

[Magi]

I have the error checking in there because it is part of my assignment. If there are errors then I have to return some kind of error code. I know it makes it more messy but I have to have it in there.

[Magi]

right now the program is exiting with code 1, cannot open file. How can I change that

#include <iostream>
#include <fstream>
#include <string>
#include "person class.h"


int main() {


std::ifstream input("person.dat");


if (!input) {
std::cerr << "cannot open file" << std::endl;
return 1;
}
while (!EOF){
person in;


input >> in.last_name;


if (input.eof()) {
std::cerr <<"no data in file" << std::endl;
return 2;
}


if (input.fail() || input.peek() != ',' || !input.ignore()) {
std::cerr <<"last name error" << std::endl;
return 3;
}


if (!getline(input, in.first_name, ',')) {
std::cerr <<"first name error" << std::endl;
return 4;
}


input >> in.monthly_pay;


if (!input) {
std::cerr <<"error with pay" << std::endl;
return 5;
}


std::ofstream stream ("output.dat");
stream << in.last_name <<"," << in.first_name << "," << in.monthly_pay << "/n"<<std::endl;
}
return
0;


}

[Elysia]

Generally, you should not use eof as a loop condition (google the why!).
It is much better to check if a read/write failed to know when you've hit the end of a file. You can test a stream by simply using it in a boolean context, such as an if statement.
The stream operators and getline also return the stream itself, you can chain operations:

if (!stream) // Last operation failed
if (!(stream >> var)) // Read operation failed
if (!std::getline(stream, var)) // Read operation failed