第十四章 重载运算与类型转换

14.1

不同点：重载运算符至少有一个操作数是类类型，而且对于部分运算符它无法保留求值顺序或短路求值属性

相同点：对于一个重载运算符来说，其优先级和结合律与对应的内置运算符保持一致

 

14.2

 1 #include <iostream>
 2 #include <vector> 
 3 #include <string>
 4  
 5 using namespace std;
 6 
 7 class Sales_data { 
 8     friend istream &operator>>(istream &is, Sales_data&);
 9     friend ostream &operator<<(ostream &os, Sales_data&);
10 public:
11     //构造函数 
12     Sales_data() = default;
13     //重载运算符
14     Sales_data &operator+=(const Sales_data&);
15 private:
16     string bookNo;                //书的ISBN 
17     unsigned units_sold = 0;    //售出的本数 
18     double revenue = 0.0;        //销售额
19 };
20 
21 istream &operator>>(istream &is, Sales_data &book)
22 {
23     is >> book.bookNo >> book.units_sold >> book.revenue;
24     return is;
25 }
26 
27 ostream &operator<<(ostream &os, Sales_data &book)
28 {
29     os << book.bookNo << " " << book.units_sold << " " << book.revenue;
30     return os;
31 }
32 
33 Sales_data &Sales_data::operator+=(const Sales_data &rhs)
34 {
35     units_sold += rhs.units_sold;
36     revenue += rhs.revenue;
37     return *this;
38 }
39 
40 Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs)
41 {
42     Sales_data total = lhs;
43     total += rhs;
44     return total;
45 }
46 
47 
48 int main()
49 {
50     Sales_data a;
51     cin >> a;
52     Sales_data b, c;
53     b = a;
54     c = a + b;
55     cout << a << endl << b << endl << c << endl;
56     return 0;
57 }

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