以下是main.h的內容
1
#include <iostream>
2#include <string>
3using namespace std;
4
5class Sales_item
6
{
7
public :
8 Sales_item(string s,int num1,float price1);
9 Sales_item();
10
~Sales_item(){}
11 Sales_item& operator =(const Sales_item& s1);
12 Sales_item& operator += (Sales_item& s1);
13 friend ostream& operator<<(ostream& out,const Sales_item& s1);
14 friend istream& operator>>(istream& in,Sales_item& s1);
15 friend bool operator ==(Sales_item& s1,Sales_item& s2); //friend是與操作數相同的
16 friend bool operator !=(Sales_item& s1,Sales_item& s2);
17 friend Sales_item operator +(Sales_item& s1,Sales_item& s2);
18 friend Sales_item operator -(Sales_item& s1,Sales_item& s2);
19private:
20 std::string isbn; //書目編號
21 int num; //書的數目
22 float total; //書的單價
23
};
24
25Sales_item::Sales_item(string s, int num1, float price1)
26{
27 isbn = s;
28 num= num1;
29 total = price1;
30}
31Sales_item::Sales_item()
32{
33 isbn = ""; //賦值不同于初始化，這里是不能用括號初始化的
34 num = 0;
35 total = 0;
36}
37Sales_item& Sales_item::operator =(const Sales_item& s1) //類外部定義的時候總是沒有加限定符
38{
39 this->isbn = s1.isbn;
40 this->num = s1.num;
41 this->total = s1.total;
42 return *this;
43}
44Sales_item& Sales_item::operator +=(Sales_item& s1)
45{
46 this->isbn += s1.isbn;
47 this->num += s1.num;
48 this->total += s1.total;
49 return *this;
50}
51ostream& operator<<(ostream& out,const Sales_item& s1) //類的外部就不能在用friend不允許位于類定義之外
52{
53 out << s1.isbn << "\t" << s1.num << "\t" << s1.total;
54 return out;
55}
56istream& operator>>(istream& in,Sales_item& s1)
57{
58 double price;
59 in >> s1.isbn >> s1.num >> price;
60 if (in)
61 s1.total = s1.num * price;
62 else
63 s1 = Sales_item();
64 return in;
65}
66bool operator ==(Sales_item& s1,Sales_item& s2)
67{
68 return s1.isbn==s2.isbn && s1.num==s2.num && s1.total==s2.total;
69}
70bool operator !=(Sales_item& s1,Sales_item& s2)
71{
72 return (s1.isbn!=s2.isbn)|| (s1.num!=s2.num)|| (s1.total!=s2.total);
73 /**//*return !(s1==s2);*/
74}
75Sales_item operator +(Sales_item& s1,Sales_item& s2)
76{
77 if (s1 == s2)
78 return Sales_item(s1.isbn,s1.num+s2.num,s1.total+s2.total);
79 else
80 return Sales_item();
81}
82Sales_item operator -(Sales_item& s1,Sales_item& s2)
83{
84 if (s1 == s2)
85 return Sales_item(s1.isbn,s1.num-s2.num,s1.total-s2.total);
86 else
87 return Sales_item();
88}
下面是main.cpp
:
1#include <iostream>
2#include "main.h"
3using namespace std;
4
5int main()
6{
7 Sales_item s1,s2;
8 cin >> s1 >> s2;
9 cout << s1 << endl << s2 << endl;
10 if (s1 == s2)
11 {
12 cout << "equal" << endl;
13 cout << s1+s2 << endl;
14
}
15 if (s1 != s2)
16 cout << "not equal" << endl;
17 return 0;
18}
當然，寫這個代碼的時候覺得很多問題都沒有考慮清楚，不過最后還是解決了問題：
1.在書寫過程中忘記了類型限定符。
2.細節問題。
3.函數的命名空間
現在我想說的是：
關于重載!=的時候遇到的問題，開始的時候我直接copy 了==的判斷，所以直接就改成了！=相&&得形式，可想而知結果肯定是錯誤的。
因為判斷不等于的時候，只要是一個不相等就不等，而如果用到了&&，那么即使有一個不等的話還是返回false，判定相等了，也就是
！=和==沒有成為一個全集，兩者不是互逆的關系。。
調試代碼的技巧很重要啊！！
posted on 2009-09-27 14:15
deercoder 閱讀(429)
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