c++的类系芥么顶一地，卧槽

C++  /  houtizong 发布于 2年前   205

摘自c＋＋primer

#ifndef SALESITEM_H#define SALESITEM_H// Definition of Sales_item class and related functions goes here#include <iostream>#include <string>class Sales_item {friend bool operator==(const Sales_item&, const Sales_item&);// other members as beforepublic:    // added constructors to initialize from a string or an istream    Sales_item(const std::string &book):              isbn(book), units_sold(0), revenue(0.0) { }    Sales_item(std::istream &is) { is >> *this; }    friend std::istream& operator>>(std::istream&, Sales_item&);    friend std::ostream& operator<<(std::ostream&, const Sales_item&);public:    // operations on Sales_item objects    // member binary operator: left-hand operand bound to implicit this pointer    Sales_item& operator+=(const Sales_item&);    // other members as before    public:    // operations on Sales_item objects    double avg_price() const;    bool same_isbn(const Sales_item &rhs) const        { return isbn == rhs.isbn; }    // default constructor needed to initialize members of built-in type    Sales_item(): units_sold(0), revenue(0.0) { }// private members as beforeprivate:    std::string isbn;    unsigned units_sold;    double revenue;};// nonmember binary operator: must declare a parameter for each operandSales_item operator+(const Sales_item&, const Sales_item&);inline bool operator==(const Sales_item &lhs, const Sales_item &rhs){    // must be made a friend of Sales_item    return lhs.units_sold == rhs.units_sold &&           lhs.revenue == rhs.revenue &&   lhs.same_isbn(rhs);}inline bool operator!=(const Sales_item &lhs, const Sales_item &rhs){    return !(lhs == rhs); // != defined in terms of operator==}using std::istream; using std::ostream;// assumes that both objects refer to the same isbninlineSales_item& Sales_item::operator+=(const Sales_item& rhs) {    units_sold += rhs.units_sold;     revenue += rhs.revenue;     return *this;}// assumes that both objects refer to the same isbninlineSales_item operator+(const Sales_item& lhs, const Sales_item& rhs) {    Sales_item ret(lhs);  // copy lhs into a local object that we'll return    ret += rhs;           // add in the contents of rhs     return ret;           // return ret by value}inlineistream& operator>>(istream& in, Sales_item& s){    double price;    in >> s.isbn >> s.units_sold >> price;    // check that the inputs succeeded    if (in)        s.revenue = s.units_sold * price;    else         s = Sales_item();  // input failed: reset object to default state    return in;}inlineostream& operator<<(ostream& out, const Sales_item& s){    out << s.isbn << "\t" << s.units_sold << "\t"         << s.revenue << "\t" <<  s.avg_price();    return out;}inlinedouble Sales_item::avg_price() const{    if (units_sold)         return revenue/units_sold;     else         return 0;}#endif