c++第九章-（运算符重载）

一些规则

1.c++不允许用户自己定义新的运算符，只能对已有的c++运算符进行重载。

2.除了五个运算符不允许重载外，其他运算符允许重载：

• .成员访问运算符
• *成员指针访问运算符
• ::与运算符
• sizeof尺寸运算符
• ?:条件运算符

3.重载运算符必须和用户定义的自定义类型的对象一起使用。（也就是说，参数不能全部都是c++的标准类型，这样约定是为了防止用户修改用于标准类型结构的运算符性质）

4.为什么运算符重载函数有两个参数，只需有一个参数？

其实是有一个参数是隐含着的，运算符函数是用this指针隐式地访问类对象的成员。

5.参数传值分三种，值传递、地址传递和引用传值。

class Complex{public:    Complex();    Complex(double r,double i);    Complex operator+(Complex &d);//“引用传值”    void print();private:    double real;    double imag;};Complex::Complex(){    real = 0;    imag = 0;}Complex::Complex(double r,double i){    real = r;    imag = i;}Complex Complex::operator+(Complex &d){    Complex c;        c.real = real + d.real;    c.imag = imag + d.imag;        return c;}void Complex::print(){    std::cout << "(" << real << "," << imag << "i)\n";}int main(int argc, const char * argv[]){    Complex c1(3,4),c2(5,-10),c3;    c3 = c1 + c2;        std::cout << "c1 = ";    c1.print();    std::cout << "c2 = ";    c2.print();    std::cout << "c1 + c2 = ";    c3.print();        return 0;}

控制台返回的结果是：

c1 = (3,4i)c2 = (5,-10i)c1 + c2 = (8,-6i)

 2.重载加减乘除操作符，实现有理数运算demo

#include <stdlib.h>class Rational{public:    Rational(int num,int denom);//num用于分子，denom用于分母        Rational operator+(Rational rhs);    Rational operator-(Rational rhs);    Rational operator*(Rational rhs);    Rational operator/(Rational rhs);        void print();private:    void normalize();//负责对分数简化    int numerator;    int denominator;};Rational::Rational(int num,int denom){    this->numerator = num;    this->denominator = denom;        normalize();}Rational Rational::operator+(Rational rhs){    int a = numerator;    int b = denominator;    int c = rhs.numerator;    int d = rhs.denominator;        int e = a * b + c * d;    int f = b * d;        return Rational(e,f);}Rational Rational::operator-(Rational rhs){    rhs.numerator = -rhs.numerator;    return operator+(rhs);}Rational Rational::operator*(Rational rhs){    int a = numerator;    int b = denominator;    int c = rhs.numerator;    int d = rhs.denominator;        int e = a * c;    int f = b * d;        return Rational(e,f);}Rational Rational::operator/(Rational rhs){    int t = rhs.numerator;    rhs.numerator = rhs.denominator;    rhs.denominator = t;        return operator*(rhs);}void Rational::print(){    if (numerator % denominator == 0)    {        std::cout << numerator / denominator;    }    else    {        std::cout << numerator << "/" << denominator;    }}void Rational::normalize(){    if (denominator < 0)//确保分母为正    {        numerator = -numerator;        denominator = -denominator;    }    //欧几里德算法    int a = abs(numerator);//求绝对值    int b = abs(denominator);        //求最大公约数    while (b > 0)    {        int t = a % b;        a = b;        b = t;    }        //分子、分母分别除于最大公约数得到最简化分数    numerator /= a;    denominator /= a;}int main(int argc, const char * argv[]){    Rational f1(2,16);    Rational f2(7,8);        Rational res = f1 + f2;    f1.print();    std::cout << " + ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        res = f1 - f2;    f1.print();    std::cout << " - ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        res = f1 * f2;    f1.print();    std::cout << " * ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        res = f1 / f2;    f1.print();    std::cout << " / ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";    return 0;}

 控制台返回的结果：

1/8 + 7/8 = 11/8 - 7/8 = -3/41/8 * 7/8 = 7/641/8 / 7/8 = 1/7

3.重载<<操作符

事实上，我们没法再现有的ostream类专门添加一个新的operator<<（）方法。

所以只能够定义一个正常的函数再外部重载这个操作符，这与重载方法的语法大同小异，唯一的区别是不再有一个对象可以用来调用<<重载函数，而不得不通过第一个输入参数向这个重载方法传递对象。

operator<<（）函数原型，std::ostream&operator<<(std::ostream &os,Ratinoal f),第一个输入参数os是将要向它写数据的那个流，他是以“引用传递”方式传递的。第二个输入参数是打算写到那个流里的数据值，不同的operator<<()重载函数就是因为这个输入参数才相互区别的。

#include <stdlib.h>class Rational{public:    Rational(int num,int denom);//num用于分子，denom用于分母        Rational operator+(Rational rhs);    Rational operator-(Rational rhs);    Rational operator*(Rational rhs);    Rational operator/(Rational rhs);        void print();private:    void normalize();//负责对分数简化    int numerator;    int denominator;        friend std::ostream &operator << (std::ostream &os,Rational f);//用于访问私有变量};Rational::Rational(int num,int denom){    this->numerator = num;    this->denominator = denom;        normalize();}Rational Rational::operator+(Rational rhs){    int a = numerator;    int b = denominator;    int c = rhs.numerator;    int d = rhs.denominator;        int e = a * b + c * d;    int f = b * d;        return Rational(e,f);}Rational Rational::operator-(Rational rhs){    rhs.numerator = -rhs.numerator;        return operator+(rhs);}Rational Rational::operator*(Rational rhs){    int a = numerator;    int b = denominator;    int c = rhs.numerator;    int d = rhs.denominator;        int e = a * c;    int f = b * d;        return Rational(e,f);}Rational Rational::operator/(Rational rhs){    int t = rhs.numerator;    rhs.numerator = rhs.denominator;    rhs.denominator = t;        return operator*(rhs);}void Rational::print(){    if (numerator % denominator == 0)    {        std::cout << numerator / denominator;    }    else    {        std::cout << numerator << "/" << denominator;    }}void Rational::normalize(){    if (denominator < 0)//确保分母为正    {        numerator = -numerator;        denominator = -denominator;    }    //欧几里德算法    int a = abs(numerator);//求绝对值    int b = abs(denominator);        //求最大公约数    while (b > 0)    {        int t = a % b;        a = b;        b = t;    }        //分子、分母分别除于最大公约数得到最简化分数    numerator /= a;    denominator /= a;}int main(int argc, const char * argv[]){    Rational f1(2,16);    Rational f2(7,8);        Rational res = f1 + f2;    f1.print();    std::cout << " + ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        res = f1 - f2;    f1.print();    std::cout << " - ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        res = f1 * f2;    f1.print();    std::cout << " * ";    f2.print();    std::cout << " = ";    res.print();    std::cout << "\n";        std::cout << f1 << " / " << f2 << " = " << (f1/f2) <<  "\n";    return 0;}std::ostream &operator << (std::ostream &os,Rational f);std::ostream &operator << (std::ostream &os,Rational f){    os << f.numerator << "/" << f.denominator;    return os;}