Sales_data.h

#ifndef SALES_DATA_H
#define SALES_DATA_H
#include <iostream>
#include <string>
class Sales_data {
    // friend
    // overloaded output operator required by exercise 14.6
    friend std::ostream &operator<<(std::ostream&, const Sales_data&);
    // overloaded input operator required by exercise 14.9
    friend std::istream &operator>>(std::istream&, Sales_data&);
    // overloaded addition operator required by exercise 14.13
    friend Sales_data operator+(const Sales_data&, const Sales_data&);
    // overloaded equality on page 561
    friend bool operator==(const Sales_data&, const Sales_data&);
    friend bool operator!=(const Sales_data&, const Sales_data&);
    // overloaded addition operator required by exercise 14.20
    friend Sales_data operator+(const Sales_data&, const Sales_data&);
public:
    // constructor
    Sales_data() = default;
    Sales_data(const std::string &s) : bookNo(s) {}
    Sales_data(const std::string &s, unsigned n, double p) :
        bookNo(s), units_sold(n), revenue(p*n) {}
    explicit Sales_data(std::istream &is) { is >> *this; }
    // member
    std::string isbn() const { return bookNo; }
    // overloaded compound-assignment operator required by exercise 14.20
    Sales_data& operator+=(const Sales_data&);
    // takes an ISBN as parameter, required by exercise 14.22
    Sales_data& operator=(const std::string&);
private:
    std::string bookNo;
    unsigned units_sold = 0;
    double revenue = 0.0;
    double avg_price() const;
};
// member functions definition
Sales_data& Sales_data::operator+=(const Sales_data& rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}
Sales_data& Sales_data::operator=(const std::string &isbn)
{
    bookNo = isbn;
    return *this;
}
// define avg_price as inline, required by exercise 7.26
inline double Sales_data::avg_price() const
{
    if(units_sold != 0)
        return revenue / units_sold;
    else
        return revenue;
}
// overloaded output operator
std::ostream& operator<<(std::ostream& os, const Sales_data& item)
{
    os << item.bookNo << " "
       << item.units_sold << " "
       << item.revenue << " "
       << item.avg_price();
    return os;
}
// overloaded input operator
std::istream& operator>>(std::istream &is, Sales_data& item)
{
    double price = 0;
    is >> item.bookNo >> item.units_sold >> price;
    if(is) // check if input invalid
        item.revenue = item.units_sold * price;
    else
        item = Sales_data(); // input failed:given the object default state
    return is;
}
bool operator==(const Sales_data &lhs, const Sales_data &rhs)
{
    return lhs.bookNo == rhs.bookNo &&
           lhs.units_sold == rhs.units_sold &&
           lhs.revenue == rhs.revenue;
}
bool operator!=(const Sales_data &lhs, const Sales_data &rhs)
{
    return !(lhs == rhs);
}
Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs)
{
    Sales_data sum = lhs;
    sum += rhs;
    return sum;
}
#endif