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) "; } 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 << " "; res = f1 - f2; f1.print(); std::cout << " - "; f2.print(); std::cout << " = "; res.print(); std::cout << " "; res = f1 * f2; f1.print(); std::cout << " * "; f2.print(); std::cout << " = "; res.print(); std::cout << " "; res = f1 / f2; f1.print(); std::cout << " / "; f2.print(); std::cout << " = "; res.print(); std::cout << " "; return 0; }
控制台返回的结果：
1/8 + 7/8 = 1 1/8 - 7/8 = -3/4 1/8 * 7/8 = 7/64 1/8 / 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 << " "; res = f1 - f2; f1.print(); std::cout << " - "; f2.print(); std::cout << " = "; res.print(); std::cout << " "; res = f1 * f2; f1.print(); std::cout << " * "; f2.print(); std::cout << " = "; res.print(); std::cout << " "; std::cout << f1 << " / " << f2 << " = " << (f1/f2) << " "; 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; }