fraction类的运算重载

重载>> 和  <<

#include <iosfwd> // 或 #include <iostream>
using std::istream;
using std::ostream;

friend istream& operator>> (istream& , Myclass& );
friend ostream& operator<< (ostream& , const Myclass& );

 

 

运算符重载举例

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//fraction.h #ifndef FRACTION_H #define FRACTION_H   #include <iostream>   class Fraction {     friend std::ostream& operator<< (std::ostream& out, const Fraction& f);     public:         Fraction(long n=0, long d=1);         virtual ~Fraction();         Fraction operator- () const//重载负号(一元运算符重载)         {             return Fraction(-num, den);         }         Fraction operator+ (const Fraction& f) const //重载加号（二元运算符重载）         {             return Fraction(num*f.den + den*f.num, den*f.den);         }         Fraction operator++ () //重载 前缀“++”         {             num += den;             return *this;         }         Fraction operator++ (int)//重载 后缀++，int是一个虚拟参数         {             Fraction f(*this);             num+= den;             return f;         }           //重载类型转换符         //1.必须重载为成员函数         //2.不需要返回类型，因为运算符本身就是返回的类型         operator long() const         {             return num/den;         }           //重载赋值运算符“=”，只能重载为成员函数。         //若不写，系统提供默认赋值（按位赋值）         //注意：返回类的引用         //一般顺序：1.判断是否是同一对象         //          2.若被赋值的对象占用了动态空间，应先释放。再申请空间赋值         //          3.返回 return *this;         /*             String& operator= (const String& s)             {                 if(&s == this) return *this;                 if(pChar) delete[] pChar;                 if(s.pChar == NULL) p = NULL;                 else                 {                     pChar = new char[strlen(s.pChar)+1];                     strcpy(pChar, s.pChar);                 }                 return *this;             }         */         Fraction& operator= (const Fraction& f)//只能重载为成员函数。         {             if(&f == this) return *this;             num = f.num;             den = f.den;             return *this;         }           Fraction& operator+= (const Fraction& f)         {             *this = *this + f;             return *this;         }           bool operator> (const Fraction& f)const         {             return num*f.den > den*f.num;         }         protected:         void standardize();//标准化         /*         标准分数：1. 分母永远为正，分数的符号由分子表示                   2. 分子分母互为质数，即最简分数         */       private:         long num;//分子         long den;//分母   };   #endif // FRACTION_H

　　

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//fraction.cpp #include "fraction.h" #include <cmath>   std::ostream& operator<< (std::ostream& out, const Fraction& f) {     if(f.num == 0)         out << "0";     else if(1 == f.den) out << f.num;     else         out << f.num << "/" << f.den;     return out; }   static long gcd(long m, long n) {//求最大公约数     int r = 0;     while(n)     {         r = m % n;         m = n;         n = r;     }     return fabs(m); } void Fraction::standardize() {     if(0L == num || 0L == den)     {         num = 0L;         den = 1L;         return;     }     if(den < 0L)     {//分数的符号让分子表示         num = -num;         den = -den;     }     long g = gcd(num,den);     num /= g;     den /= g; }   Fraction::Fraction(long n, long d):num(n),den(d) {     standardize(); }   Fraction::~Fraction() {     //dtor }