Reading to end of file with istream_iterator and istream overload

Question

I'm having some trouble reading data from a file into a vector of Orders.

Code:

#include <string>
#include <vector>
#include <fstream>
#include <iostream>
#include <iterator>

using namespace std;

class Purchase;

class Order {
public:
    string name;
    string address;
    vector<Purchase> items;
};

class Purchase {
public:
    string product_name;
    double unit_price;
    int count;
    Purchase() {}
    Purchase(string pn, double up, int c) :product_name(pn), unit_price(up), count(c) {}
};

istream& operator>>(istream& in, Order& o)
{
    string p_name;
    double u_price;
    int p_count;

    getline(in, o.name);
    getline(in, o.address);
    getline(in, p_name);
    in >> u_price >> p_count;

    o.items.push_back(Purchase(p_name, u_price, p_count));

    return in;
}

ostream& operator<<(ostream& out, const Purchase& p)
{
    out << p.product_name << '\n'
        << p.unit_price << '\n'
        << p.count << '\n';
    return out;
}

ostream& operator<<(ostream& out, const Order& o)
{
        out << '\n' << o.name << '\n'
            << o.address << '\n'
            << o.item << '\n';
        return out;
}

int main()
{
    cout << "Enter file to read orders from: \n";
    string file;
    cin >> file;
    ifstream is(file.c_str());

    istream_iterator<Order> ii(is);
    istream_iterator<Order> eos;
    ostream_iterator<Order> oo(cout);
    vector<Order> orders(ii, eos);

    copy(orders.begin(), orders.end(), oo);
}

I have 3 main questions.

1) When I take out the o.item bug in the ostream overload to test output, it only outputs the first entry in the file. The txt file is structured in groups of 5 lines of data that are supposed to be read into vector orders.

Right now the txt file has 10 "orders", but it only reads the first one into the orders vector. I probably need to implement some kind of end of file operation, but I'm not sure how to do this with the istream overload and iterator. This is the biggest problem and if I can figure this out I think I'll probably be okay with the next 2 questions.

2) When that problem is fixed. I will need to deal with the output of o.item (the vector of Purchases in orders which currently can't be output because there is no element being specified). Obviously I need to specify the element to output and I've considered just using a static int and incrementing it, but this would need to be reset for every separate Order, which leads to question 3...

3) If the same name/address are read in as a previous read, I need the program to understand that it is the same "order" being read in and to simply add another object to that Order's Purchases vector rather than creating a new order. I'm thinking about using find() to check if that name already exists in order, and in that case doing nothing with the name/address inputs, but if there is a better way I'd like to know.

Sorry if this is kind of long. If more explanation is needed I'd be happy to elaborate. Any help is appreciated. Thanks.

P.S. Here is an example of input output at the moment if I specify the o.item output to be o.item[0].

Text file has:

John Smith
117 One Tree Hill
Trampoline
600.00
1 

//... 9 more Orders like this

Output is:

John Smith
117 One Tree Hill
Trampoline
600.00
1
//... Nothing after this....

Answer 1

I haven't looked at your code in detail, but I will give one sentence of advice:

"Do not mix formatted and unformatted input. And in fact, do not use formatted input from files or user input at all."

OK, that was two sentences.

Answer 2

Regarding question #3, you could use a multimap instead of a vector.

First, assume you split your Order class up as follows:

class Customer{
public:
    string name;
    string address;
};

class Purchase {
public:
    string product_name;
    double unit_price;
    int count;
    Purchase() {}
    Purchase(string pn, double up, int c) :product_name(pn), unit_price(up), count(c) {}
};

class Order {
    Customer c;
    std::vector<Purchase> p;
};

Now you can simply create a std::multimap<Customer, Purchase>. Adding a customer/purchase pair does exactly what you want: If the customer doesn't already exist, he is added, otherwise the purchase is just added to the existing customer.

Of course, for this to work, you need to define a comparer as well. Simplest way might just be to define operator < for the Customer class. Implement it by comparing the name and disregarding the address.

As for your other questions, avoid mixing getline and stream_iterators. It's not wrong per se, but it gets pretty tricky because getline reads a line at a time, and stream iterators just read to the next whitespace.

Honestly, the C++ IOStreams library is pretty awful to use in general. Since your data format is already cleanly line-separated already, I'd probably just ditch the stream iterators and use getline everywhere.

Answer 3

The problem you have is very simple. In fact your code is pretty clear :)

All what you have to add are those simple lines:

istream& operator>>(istream& in, Order& o)
{
    string p_name;
    double u_price;
    int p_count;

    getline(in, o.name);
    getline(in, o.address);
    getline(in, p_name);

    in >> u_price >> p_count;

    //
    while(in.peek() == '\n' || in.peek() == ' ')
    {
     in.ignore();
    }
    //

    o.items.push_back(Purchase(p_name, u_price, p_count));

    return in;
}

The reason is that when using >> it leaves the newline character in the stream unlike getline. You can search Stackoverflow about streams in general there are a lot of great explanations about the issue.

Also, you don't have anything called item in Order. What you have is a vector of Purchase:

ostream& operator<<(ostream& out, const Order& o)
{
        out << '\n' << o.name << '\n'
            << o.address << '\n';
     //
     for(vector<Purchase>::const_iterator i = o.items.begin();
      i != o.items.end(); i++)
     {
      out << *i << '\n';
     }
        //

        return out;
}