C++中使用类(重载,友元函数,转换函数等)
C++中使用类(重载,友元函数,转换函数等)
说下C++里的操作符重载和以后的内容。C++中有个operator操作符概念。如果想重载+运算符,那么需要写成operator+()。一般两个数相加是这么调用的:- a = b+c; == a = b.operator+(c);
重点介绍友元函数。因为重载了运算符后可能出现类似:
- a = 1.5 + c;
然后贴三段代码,注释写的还算详细。大家可以复制后去运行下看下结果。代码是从C++Primer Plus里抄过来的。
mytime0.h
- #ifndef MYTIME0_H_
- #define MYTIME0_H_
- #include <iostream>
- class Time
- {
- private:
- int hours;
- int minutes;
- public:
- Time();
- Time(int h, int m = 0);
- void AddMin(int m);
- void AddHr(int h);
- void Reset(int h = 0, int m = 0);
- Time Sum(const Time & t)const;
- // 接下来时重载+运算符的函数
- Time operator+(const Time & t)const;
- void Show()const;
- // 重载-运算符的函数
- Time operator-(const Time & t)const;
- // 重载*运算符的函数
- Time operator*(double n)const;
- // 友元函数 类似 a+b 的原型是 a.operator+(b); 所以如果 5*a 则5没有那个重载的函数,这时就不能使用类的成员函数了,需要友元函数来进行操作,类友元函数也就是非成员函数
- friend Time operator*(double m, const Time & t){return t * m;} //内联函数,调用该类的成员函数,这里也就是上面那个函数。
- // 友元函数。对于那些非成员重载操作符函数来说,操作符左面的操作数对应函数的第一个参数。类似 c = a+b 类似于 c = operator+(a,b)
- friend std::ostream & operator<<(std::ostream & os, const Time & t);
- };
- #endif
- #include <iostream>
- #include "mytime0.h"
- Time::Time()
- {
- hours = minutes = 0;
- }
- Time::Time(int h, int m)
- {
- hours = h;
- minutes = m;
- }
- void Time::AddMin(int m)
- {
- minutes += m;
- hours += minutes / 60;
- minutes %= 60;
- }
- void Time::AddHr(int h)
- {
- hours += h;
- }
- void Time::Reset(int h, int m)
- {
- hours = h;
- minutes = m;
- }
- Time Time::Sum(const Time & t)const
- {
- Time sum;
- sum.minutes = minutes + t.minutes;
- sum.hours = hours + t.hours + sum.minutes/60;
- sum.minutes %= 60;
- return sum;
- }
- // 重载加号运算符的版本
- Time Time::operator+(const Time & t)const
- {
- Time sum;
- sum.minutes = minutes + t.minutes;
- sum.hours = hours + t.hours + sum.minutes/60;
- sum.minutes %= 60;
- return sum;
- }
- Time Time::operator-(const Time & t)const
- {
- Time diff;
- int tot1, tot2;
- tot1 = t.minutes + 60 * t.hours;
- tot2 = minutes + 60 * hours;
- diff.minutes = (tot2 - tot1) % 60;
- diff.hours = (tot2 - tot1) / 60;
- return diff;
- }
- Time Time::operator*(double n)const
- {
- Time result;
- long totalminutes = hours * n * 60 + minutes * n;
- result.hours = totalminutes / 60;
- result.minutes = totalminutes % 60;
- return result;
- }
- std::ostream & operator<<(std::ostream & os, const Time & t)
- {
- os << t.hours << "hours, " << t.minutes << " minutes";
- return os;
- }
- void Time::Show()const
- {
- std::cout << hours << " hours, " << minutes << " minutes";
- }
- //usetime0.cpp
- #include <iostream>
- #include "mytime0.h"
- int main()
- {
- using std::cout;
- using std::endl;
- Time planning;
- Time coding(2, 40);
- Time fixing(5, 55);
- Time total;
- cout << "planning time = ";
- planning.Show();
- cout << endl;
- cout << "coding time = ";
- coding.Show();
- cout << endl;
- cout << "fixing time = ";
- fixing.Show();
- cout << endl;
- // total = coding.Sum(fixing);
- // 重载加号运算符的版本
- total = coding + fixing;
- cout << "coding + fixing = ";
- total.Show();
- cout << endl;
- Time morefixing(3 ,20);
- cout << "more fixing time = ";
- morefixing.Show();
- cout << endl;
- total = morefixing.operator+(total);
- cout << "morefixing.operator+(total) = ";
- total.Show();
- cout << endl;
- Time aida(3, 35);
- Time tosca(2, 48);
- Time temp;
- cout << "Aida and TOsca:\n";
- cout << aida <<"; " << tosca << endl;
- temp = aida + tosca; // operator+()
- cout << "Aida + Tosca: " << temp << endl;
- temp = aida*1.17;
- cout << "Aida *1.17: " << temp << endl;
- cout << "10 * Tosca: " << 10 * tosca << endl;
- return 0;
- }
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