C++面向对象程序设计的一些知识点（5）

摘要：运算符能给程序员提供一种书写数学公式的感觉，本质上运算符也是一种函数，因此有类内部运算符和全局运算符之分，通过重载，运算符的“动作”更加有针对性，编写代码更像写英文文章。

1、C++标准允许将运算符重载为类成员或者全局的，一般如果是全局的话，为了效率，都是把它们定义为类友元函数。

 1 /*
 2 ** 重载全局运算符“+”、“-”，代码如下：
 3 */
 4 #include <iostream>
 5 
 6 using namespace std;
 7 
 8 //class Complex;
 9 //Complex operator+(const Complex &c1, const Complex &c2);
10 //Complex operator-(const Complex &c1, const Complex &c2);
11 // 我的疑问：声明为全局的有什么好处的，或者说有什么必要的么？
12 class Complex
13 {
14 public:
15     Complex(double real = 0.0, double image = 0.0)
16     {
17         this->real = real;
18         this->image = image;
19     }
20 public:
21     void displayComplex()
22     {
23         if(image >= 0)
24             cout << "(" << real << '+' << image << 'i' << ")";
25         else
26             cout << "(" << real << image << 'i' << ")";
27     }
28     friend Complex operator+(const Complex &c1, const Complex &c2);
29     friend Complex operator-(const Complex &c1, const Complex &c2);
30 private:
31     double real;
32     double image;
33 };
34 
35 Complex operator+(const Complex &c1, const Complex &c2)
36 {
37     Complex complexTemp;
38     complexTemp.real = c1.real + c2.real;
39     complexTemp.image = c1.image + c2.image;
40     return complexTemp;
41 }
42 Complex operator-(const Complex &c1, const Complex &c2)
43 {
44     Complex complexTemp;
45     complexTemp.real = c1.real - c2.real;
46     complexTemp.image = c1.image - c2.image;
47     return complexTemp;
48 }
49 int main()
50 {
51     Complex c, c1(1.1, 2.2), c2(3.3, 4.4);
52     c = c1 + c2;
53     c = c1 - c2; // operator-(c1, c2);
54     c1.displayComplex();
55     cout << "-";
56     c2.displayComplex();
57     cout << "=";
58     c.displayComplex();
59     cout << endl;
60 
61     int i;
62     cin >> i;
63     return 0;
64 }

重载为友元函数