C++面向对象：实现Fraction类 | variadic templates

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//Fraction.h #pragma once #include <iostream> #include <string>   using namespace std;   int& __gcd(int&, int&);   class Fraction { public:     explicit Fraction(int num, int den = 1): m_numerator(num), m_denominator(den) {         int t = __gcd(num, den); //这里不能传(m_numerator, m_denominator), 因为原函数是引用传参         //约分         m_numerator /= t;         m_denominator /= t;     }       operator double() const { return (double)m_numerator / m_denominator; } //conversion function 转换函数     double operator +(const double& d) const { return (double)m_numerator / m_denominator + d; }     Fraction operator +(const Fraction&) const;     operator string() const { return to_string(m_numerator) + '/' + to_string(m_denominator); } //转换函数       bool operator < (const Fraction& f) {         //a/c = ad/cd, b/d = bc/cd         return m_numerator * f.m_denominator < m_denominator * f.m_numerator;     }   private:     int m_numerator;     int m_denominator;       friend int& __gcd(int&, int&); };   Fraction Fraction::operator +(const Fraction& f) const {     //a/c + b/d = (ad + bc) / cd     int num = m_numerator * f.m_denominator + m_denominator * f.m_numerator;     int den = m_denominator * f.m_denominator;     return Fraction(num, den); }   inline int& __gcd(int& a, int& b) {     while (a % b != 0) {         int t = a % b;         a = b;         b = t;     }     return b; }   //模板泛化 template<class T> inline const T& min(const T& a, const T& b) {     return b < a ? b : a; }   //模板特化 template<> struct hash<Fraction> {     double operator()(const Fraction& f) { return double(f); } };     //variadic templates, 可变参数模板 void show() { cout << endl; } //传入firstArg和args...均为空时调用该函数   template<typename T, typename... Types> void show(const T& firstArg, const Types&... args) {     cout << firstArg << " " ;     show(args...); }

　　

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//Fraction.cpp #include "Fraction.h"   int main() {           cout << __cplusplus << endl; //C++11           //conversion function     Fraction f0(3);     Fraction f1(3, 2);     Fraction f2(9, 6);     show(f0, f1, f2);     show(string(f0), string(f1), string(f2));     show(f0 + f1, f1 + 2.7);       Fraction f3(f0 + f2);     Fraction f4 = f0 + f2;     double f5 = f0 + 2.1;     //Fraction f6 = f0 + 2.1; //non-explicit ctor时, 情况一: 2.1由double转换为Fraction, 情况二: f6由double转换为Fraction, 会引起ambiguous Err     //Fraction f7 = f0 + 2.1; //explicit ctor时, double转化为Fraction的隐式转换被禁用, 本行报错     show(f3, f4, f5);     //show(f6, f7);       bool b01 = f0 < f1;     bool b12 = f1 < f2;     bool b03 = f0 < f3;     show(b01, b12, b03);       Fraction f01 = min(f0, f1);     Fraction f12 = min(f1, f2);     Fraction f03 = min(f0, f3);     show(string(f01), string(f12), string(f03));           show(hash<Fraction>()(f12));       return 0; }

　　执行结果：

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201402 3 1.5 1.5 3/1 3/2 3/2 4.5 4.2 4.5 4.5 5.1 0 0 1 3/2 3/2 3/1 1.5