实现一个整数类

 1 #ifndef INTEGER_H_
 2 #define INTEGER_H_
 3 
 4 #include <iostream>
 5 
 6 class Integer
 7 {
 8 
 9     friend std::ostream &operator<< (std::ostream &os, const Integer &i);
10     friend std::istream &operator>> (std::istream &is, Integer &i);
11 
12 public:
13     Integer(int data = 0);  // int -> Integer
14     Integer &operator=(int data);
15 
16     Integer &operator++(); //++i
17     Integer operator++(int); //i++
18 
19     operator int() //类型转化
20     { return data_; }
21 
22 private:
23     int data_;
24 };
25 
26 
27 #endif /* INTEGER_H_ */

 1 #include "Integer.h"
 2 
 3 using namespace std;
 4 
 5 
 6 Integer::Integer(int data)
 7     :data_(data)
 8 {
 9 }
10 
11 ostream &operator<< (ostream &os, const Integer &i)
12 {
13     return os << i.data_;
14 }
15 
16 istream &operator>> (istream &is, Integer &i)
17 {
18     int temp = i.data_;  //backup; 
19     is >> i.data_;
20     if(!is) //输入失败
21     {
22         i.data_ = temp; //还原
23     }
24         
25     return is;
26 }
27 
28 
29 Integer &Integer::operator++()
30 {
31     //++i = 5;
32     ++data_;
33 
34     return *this;
35 }
36 
37 Integer Integer::operator++(int)
38 {
39     //i++ 不能为左值
40     Integer temp(*this);  //备份old
41     ++data_;
42 
43     return temp;
44 }
45 
46 Integer &Integer::operator=(int data)
47 {
48     data_ = data;
49     return *this;
50 }