1 friend 函数类型 operator 运算符（形参表） 
2 { 
3     函数体; 
4 } 

 1 //运算符重载:成员函数方式
 2 #include <iostream>
 3 using namespace std;
 4 
 5 class complex //复数类
 6 {
 7 public:
 8     complex(){ real = imag = 0;}
 9     complex(double r, double i)
10     {
11         real = r;
12         imag = i;
13     }
14     complex operator + (const complex &c);
15     complex operator - (const complex &c);
16     complex operator * (const complex &c);
17     complex operator / (const complex &c);
18 
19     friend void print(const complex &c); //友元函数
20 
21 private:
22     double real; //实部
23     double imag; //虚部
24 
25 };
26 
27 inline complex complex::operator + (const complex &c) //定义为内联函数,代码复制，运算效率高
28 {
29     return complex(real + c.real, imag + c.imag);
30 }
31 
32 inline complex complex::operator - (const complex &c)
33 {
34     return complex(real - c.real, imag - c.imag);
35 }
36 
37 inline complex complex::operator * (const complex &c)
38 {
39     return complex(real * c.real - imag * c.imag, real * c.real + imag * c.imag);
40 }
41 
42 inline complex complex::operator / (const complex &c)
43 {
44     return complex( (real * c.real + imag * c. imag) / (c.real * c.real + c.imag * c.imag), 
45         (imag * c.real - real * c.imag) / (c.real * c.real + c.imag * c.imag) );
46 }
47 
48 void print(const complex &c) 
49 {
50     if(c.imag < 0)
51         cout<<c.real<<c.imag<<‘i‘<<endl;
52     else
53         cout<<c.real<<‘+‘<<c.imag<<‘i‘<<endl;
54 }
55 
56 int main()
57 {    
58     complex c1(2.0, 3.5), c2(6.7, 9.8), c3;
59     c3 = c1 + c2;
60     cout<<"c1 + c2 = ";
61     print(c3); //友元函数不是成员函数，只能采用普通函数调用方式,不能通过类的对象调用
62 
63     c3 = c1 - c2;
64     cout<<"c1 - c2 = ";
65     print(c3);
66 
67     c3 = c1 * c2;
68     cout<<"c1 * c2 = ";
69     print(c3);
70 
71     c3 = c1 / c2;
72     cout<<"c1 / c2 = ";
73     print(c3);
74     return 0;
75 }