1. 运算符

2. 自定义数据类型与运算符重载

3. 运算符重载

4. 运算符重载为普通函数

class Complex{
	public:
		Complex(double r = 0.0, double i = 0.0){
			real = r;
			imaginary = i;
		}
		double real;      //real part
		double imaginary; //imaginary part
};
Complex operator+ (const Complex & a, const Complex & b)
{
	return Complex(a.real + b.real, a.imaginary + b.imaginary);
}//"类名(参数表)"就代表一个对象

Complex a(1,2), b(2, 3), c;
c = a + b;//相当于什么？

重载为普通函数时，参数个数为运算符目数

5. 运算符重载为成员函数

class Complex{
	public:
		Complex(double r = 0.0, double m = 0.0):
			real(r), imaginary(m){ }    //constructor
		Complex operator+(const Complex &); //addition
		Complex operator-(const Complex &); //subtraction
	private:
		double real;      //real part
		double imaginary; //imaginary part
};
//Overloaded addition operator
Complex Complex::operator+(const Complex & operand2){
	return Complex(real + operand2.real,
			imaginary + operand2.imaginary);
}
//Overloaded subtraction operator
Complex Complex::operator-(const Complex & operand2){
	return Complex(real - operand2.real,
   			imaginary - operand2.imaginary);
}
int main(){
	Complex x, y(4.3, 8.2), z(3.3, 1.1);
	x = y + z;
	x = y - Z;
	return 0;
}

重载为成员函数时，参数个数为运算符数目减一

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【1】北京大学信息技术学院《程序设计实习》