Question

I quite recently learned about the C++ classes friend keyword and the uses in serialization and now I need some help in getting it to work.

I have no problem serializing my class to a file, it’s working great, however i’m having a hard time trying to read this file into a vector container. I’m sure I need a loop in my code that reads line by line, but since the class has different types I guess I can’t use std::getline() and also maybe that approach wouldn’t use the istream method i implemented?
A sample output file would be:

Person 1
2009
1

Person 2
2001
0

My code:

class SalesPeople {
    friend ostream &operator<<(ostream &stream, SalesPeople salesppl);
    friend istream &operator>>(istream &stream, SalesPeople &salesppl);

    private:
        string fullname;
        int employeeID;
        int startYear;
        bool status;
};

ostream &operator<<(ostream &stream, SalesPeople salesppl)
{
    stream << salesppl.fullname << endl;
    stream << salesppl.startYear << endl;
    stream << salesppl.status << endl;
    stream << endl;
    return stream;
}

istream &operator>>(istream &stream, SalesPeople &salesppl)
{
    stream >> salesppl.fullname;
    stream >> salesppl.startYear;
    stream >> salesppl.status;
    // not sure how to read that empty extra line here ?
    return stream;
}

// need some help here trying to read the file into a vector<SalesPeople>
SalesPeople employee;
vector<SalesPeople> employees;

ifstream read("employees.dat", ios::in);
if (!read) {
   cerr << "Unable to open input file.\n";
   return 1;
}

// i am pretty sure i need a loop here and should go line by line 
// to read all the records, however the class has different
// types and im not sure how to use the istream method here.

read >> employee;
employees.push_back(employee);

By the way, I know that the Boost library has a great serialization class, however I’m trying to learn how serialization would work using the STL library for now.
Thanks a lot in advance for any help that you can give me and for getting me in the right track!

Answer 1

It looks like you pretty much have all the code you need already! I copied your code and compiled it with some changes to read the SalesPeople in from a file in a loop. I will include the changes below, but since this is for your homework, you may just want to read and think about the following hints before looking at the code.

• For reading the SalesPeople in a
  loop, I would recommend that you take
  a look at this FAQ. It has an
  example of almost exactly what you
  need. FAQ 15.4 will also help
  you, I believe.

• For your question on how to handle
  the extra empty line when reading
  from the file, check out this
  link. You can very simply
  extract whitespace this way.

• As jfclavette suggested, I would
  recommend looking into
  std::getline for reading in the
  SalesPerson’s full name, since you
  need everything on that line into one
  string.

I have one question for you, though: what about the employeeID? I notice that it is being ignored in your sample code. Is that on purpose?

And now, if you still need help, you can check out the code I wrote to get this to work:

istream &operator>>(istream &stream, SalesPeople &salesppl)
{
    //stream >> salesppl.fullname;
    getline(stream, salesppl.fullname);
    stream >> salesppl.startYear;
    stream >> salesppl.status;
    // not sure how to read that empty extra line here ?
    stream >> ws;
    return stream;
}

while(read >> employee)
{
    // cout << employee; // to verify the input, uncomment this line
    employees.push_back(employee);
}

Also, as jfclavette suggested, it may not be a bad idea to add some input validation (check the stream status after reading from it and verify that it is still good). Although I would recommend using the while() loop for the reasons stated in FAQ 15.5.