C++快速入门 第二十七讲：运算符左移<<重载

一般来说，在调用operator<<()重载函数时，传递给它的是哪一个流，它返回的就应该是那个流的一个引用。

实例：左移操作符重载

  1 #include <iostream>
  2 #include <string>
  3 #include <math.h> 
  4 
  5 using namespace std;
  6 class Rational//定义基类
  7 {
  8 public:
  9     Rational(int num,int denom); //构造器 num = 分子，denom = 分母 
 10     
 11     Rational operator+(Rational rhs);// rhs == right hand side(右手边参数) 
 12     Rational operator-(Rational rhs);
 13     Rational operator*(Rational rhs);
 14     Rational operator/(Rational rhs);
 15     
 16 private:
 17     void normalize();//负责对分数的简化处理
 18     
 19     int numerator; //分子
 20     int denominator; //分母 
 21     
 22     friend ostream& operator<<(ostream& os,Rational f);//传递给它的是哪一个流，它返回的就是那个流的一个引用
 23 }; 
 24 
 25 Rational::Rational(int num,int denom)//构造函数实现 
 26 {
 27     numerator = num;
 28     denominator = denom;
 29     
 30     normalize(); 
 31 } 
 32 //normalize()对分数进行简化操作包括：
 33 //1.只允许分子为负数，如果分母为负数则把负数挪到分子部分，如1/-2==-1/2 
 34 //2.利用欧几里德算法(辗转求余原理)将分数进行简化:2/10 => 1/5 
 35 
 36 void Rational::normalize()
 37 {
 38     //确保分母为正
 39     if( denominator < 0) 
 40     {
 41         numerator = -numerator;
 42         denominator = -denominator;
 43     }
 44     //欧几里德算法 
 45     int a = abs(numerator);
 46     int b = abs(denominator);
 47     
 48     //求出最大公约数
 49     while(b>0)
 50     {
 51         int t = a % b;//取余 
 52         a = b;
 53         b = t;
 54     }
 55      
 56      //分子、分母分别除以最大公约数得到最简化分数
 57      numerator /= a;
 58      denominator /= a; 
 59 }
 60 //a   c   a*d   c*b   a*d + c*d
 61 //- + - = --- + --- = ----------
 62 //b   d   b*d   b*d      b*d
 63 Rational Rational::operator+(Rational rhs)//分数的加运算 
 64 {
 65     int a = numerator;
 66     int b = denominator;
 67     int c = rhs.numerator;
 68     int d = rhs.denominator;
 69     
 70     int e = a*b + c*d;
 71     int f = b*d;
 72     
 73     return Rational(e,f);
 74 }
 75 //a   c   a   -c
 76 //- - - = - + -- 
 77 //b   d   b   d 
 78 Rational Rational::operator-(Rational rhs)//分数的减运算 
 79 {
 80     rhs.numerator = -rhs.numerator; //被减数分子取负数 
 81     return operator+(rhs);
 82 }
 83 //a   c   a*c
 84 //- * - = --- 
 85 //b   d   b*d 
 86 Rational Rational::operator*(Rational rhs)//分数的乘运算
 87 {
 88     int a = numerator;
 89     int b = denominator;
 90     int c = rhs.numerator;
 91     int d = rhs.denominator;
 92     
 93     int e = a*c;
 94     int f = b*d;
 95     
 96     return Rational(e,f);
 97 }
 98 //a   c   a   d
 99 //- / - = - * - 
100 //b   d   b   c
101 Rational Rational::operator/(Rational rhs)//分数的除运算
102 {
103     //rhs的分子分母互换 
104     int t = rhs.numerator;
105     rhs.numerator = rhs.denominator;
106     rhs.denominator = t;
107     
108     return operator*(rhs);
109 }
110 
111 ostream& operator<<(ostream& os,Rational f);//函数声明 
112 
113 int main()
114 {
115     Rational f1(2,16);//定义f1对象，且传入(2,16)参数 
116     Rational f2(7,8);
117     
118     //测试有理数加法运算 
119     cout << f1 << " + " << f2 << " == " << (f1+f2) << "\n"; // 左移操作符<<已经被重载了 
120     
121     //测试有理数减法运算 
122      cout << f1 << " - " << f2 << " == " << (f1-f2) << "\n"; //<< f1中由于f1属于Rational类型，将自动转到打印分数形式输出 
123     
124     //测试有理数乘法运算 
125      cout << f1 << " * " << f2 << " == " << (f1*f2) << "\n";//<< "+"中由于<<后面参数是字符串，所以使用系统默认的打印 
126     
127     //测试有理数除法运算 
128     cout << f1 << " / " << f2 << " == " << (f1/f2) << "\n"; 
129     
130     return 0;
131 }
132 ostream& operator<<(ostream& os,Rational f)//并不属于Rational类，是一个独立的函数 
133 {
134     if(f.numerator % f.denominator == 0)
135     os << f.numerator / f.denominator;
136     else 
137     os << f.numerator << "/" << f.denominator;//打印分数 
138     return os; 
139 }