C++学习基础八——重载输入和输出操作符

 1 class Sales_Item
 2 {
 3     //注意：形参为引用时，实参和形参才指向共同的对象，否则修改形参的数据不影响实参。 
 4 friend ostream &operator<< (ostream &out,const Sales_Item &item);
 5 friend istream &operator >> (istream &in,Sales_Item & item);
 6 public :
 7     Sales_Item()
 8     {
 9         count = 0;
10         price = 0;
11     }    
12     Sales_Item(string &book,int number,double unit)
13     {
14         isbn = book;
15         count = number;
16         price = unit * number;
17     }
18     
19 private:
20     string isbn;
21     int count;
22     double price;
23 };
24 
25 ostream &operator<< (ostream &out,const Sales_Item &item)
26 {
27     out<<item.isbn<<" , "<<item.count<<" , "<<item.price<<endl;
28     return out;
29 }
30 
31 istream &operator>> (istream &in,Sales_Item &item)
32 {
33     double price;
34     in >> item.isbn >> item.count >> price;
35     if(in)
36     {
37         item.price = price * item.count;
38     }
39     else
40     {
41         item =  Sales_Item();
42     }
43 
44     return in;
45 }
46 int main()
47 {
48     string s("0-123-12345-X");
49     Sales_Item item(s,10,12.00);
50     cout<<item<<endl;
51     
52     cin>>item;
53     cout<<item<<endl;
54     cout<<"ok"<<endl;
55     return 0;
56 }