C++重载＞＞和＜＜输入和输出运算符）

在C++中，标准库本身已经对左移运算符<<和右移运算符>>分别进行了重载，使其能够用于不同数据的输入输出，但是输入输出的对象只能是 C++ 内置的数据类型（例如 bool、int、double 等）和标准库所包含的类类型（例如 string、complex、ofstream、ifstream 等）。

如果我们自己定义了一种新的数据类型，需要用输入输出运算符去处理，那么就必须对它们进行重载。本节以前面的 complex 类为例来演示输入输出运算符的重载。

其实 C++ 标准库已经提供了 complex 类，能够很好地支持复数运算，但是这里我们又自己定义了一个 complex 类，这样做仅仅是为了教学演示。

本节要达到的目标是让复数的输入输出和 int、float 等基本类型一样简单。假设 num1、num2 是复数，那么输出形式就是：

#include <iostream>
using namespace std;
class complex
{
public:
    complex();
    complex(double a);
    complex(double a, double b);
    friend complex operator+(const complex & A, const complex & B);
    friend complex operator-(const complex & A, const complex & B);
    friend complex operator*(const complex & A, const complex & B);
    friend complex operator/(const complex & A, const complex & B);
    friend istream &operator>>(istream & in ,complex & A);
    friend ostream &operator<<(ostream & out ,complex & A);
    void display()const;
private:
    double real;   //复数的实部
    double imag;   //复数的虚部
};
complex::complex()
{
    real = 0.0;
    imag = 0.0;
}
complex::complex(double a)
{
    real = a;
    imag = 0.0;
}
complex::complex(double a, double b)
{
    real = a;
    imag = b;
}
//打印复数
void complex::display()const
{
    cout<<real<<" + "<<imag<<" i ";
}
//重载加法操作符
complex operator+(const complex & A, const complex &B)
{
    complex C;
    C.real = A.real + B.real;
    C.imag = A.imag + B.imag;
    return C;
}
//重载减法操作符
complex operator-(const complex & A, const complex &B)
{
    complex C;
    C.real = A.real - B.real;
    C.imag = A.imag - B.imag;
    return C;
}
//重载乘法操作符
complex operator*(const complex & A, const complex &B)
{
    complex C;
    C.real = A.real * B.real - A.imag * B.imag;
    C.imag = A.imag * B.real + A.real * B.imag;
    return C;
}
//重载除法操作符
complex operator/(const complex & A, const complex & B)
{
    complex C;
    double square = B.real * B.real + B.imag * B.imag;
    C.real = (A.real * B.real + A.imag * B.imag)/square;
    C.imag = (A.imag * B.real - A.real * B.imag)/square;
    return C;
}

//重载输入操作符
istream & operator>>(istream & in ,complex & A)
{
    in >>A.real>>A.imag;
    return in ;
}

//重载输出操作符
ostream & operator<<(ostream &out ,complex &A)
{
    out <<A.real<<"+"<<A.imag<<" i ";
    return  out ;
}




int main()
{
    complex c1(3, 4);
    complex c2(1, 2);
    complex c3;

    c3 = c1 + c2;
    cout<<"c1 + c2 = "<<c3<<endl;
    //c3.display();
    //cout<<endl;
    c3 = c1 - c2;
    cout<<"c1 - c2 = "<<c3<<endl;
    //c3.display();
    //cout<<endl;
    c3 = c1 * c2;
    cout<<"c1 * c2 = "<<c3<<endl;
    //c3.display();
    //cout<<endl;
    c3 = c1 / c2;
    cout<<"c1 / c2 = "<<c3<<endl;
    //c3.display();
    //cout<<endl;
    return 0;
}

c1 + c2 = 4+6 i 
c1 - c2 = 2+2 i 
c1 * c2 = -5+10 i 
c1 / c2 = 2.2+-0.4 i