【C++】学习笔记五十一——运算符重载

运算符重载

可对运算符进行重载，将运算符扩展到自定义类型。

operator【运算符】(argument-list)

例如：operator+()重载+运算符。【运算符】必须是有效的C++运算符，不能虚构一个新的符号。不能有operator@()这样的函数，但可以有operator[]()，因为[]是数组索引运算符。

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实例：计算时间

程序11.1 mytime0.h

#ifndef MYTIME0_H_#define MYTIME0_H_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;    void Show() const;};#endif // !MYTIME0_H_

Time类提供了用于调整和重新设置时间、显式时间、将两个时间相加的方法。
程序11.2 mytime0.cpp

#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;}void Time::Show() const{    std::cout << hours << " hours, " << minutes << " minutes";}

程序11.3 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);    cout << "coding.Sum(fixing) = ";    total.Show();    cout << endl;    system("pause");    return 0;}

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添加加法运算符

程序11.4 mytime1.h

#ifndef MYTIME1_H_#define MYTIME1_H_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 operator+(const Time &t) const;    void Show() const;};#endif

程序11.5 mytime1.cpp

#include <iostream>#include "mytime1.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::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;}void Time::Show() const{    std::cout << hours << " hours, " << minutes << " minutes";}

程序11.6 usetime1.cpp

#include <iostream>#include "mytime1.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 + fixing;    cout << "coding + fixing = ";    total.Show();    cout << endl;    Time morefixing(3, 28);    cout << "more fixing time = ";    morefixing.Show();    cout << endl;    total = morefixing.operator+(total);    cout << "morefixing.operator+(total) = ";    total.Show();    cout << endl;    system("pause");    return 0;}

operator+()函数的名称使得可以使用函数表示法或运算符表示法来调用它，编译器将根据操作数的类型来确定如何做。

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重载限制

运算符重载的限制：

1. 重载后的运算符必须至少由一个操作数是用户定义的类型，这将防止用户为标准类型重载运算符。
2. 使用运算符时不能违反运算符原来的句法规则。例如：不能将求模运算符（%）重载成使用一个操作数int x; % x;//错误；同样，不能修改运算符的优先级。
3. 不能创建新运算符。例如，不能定义operator**()函数来表示求幂。
4. 不能重载下面的运算符：sizeof运算符；成员运算符（.）；成员指针运算符（.*）；条件运算符（?:）；typeid；强制类型转换运算符（const_cast 、dynamic_cast、 reinterpret_cast 、static_cast）
5. 下面的运算符只能通过成员函数进行重载：赋值运算符（=）;函数调用运算符（()）；下标运算符（[]）；指针访问类成员运算符（->）。