重载<<运算符

Question

我只是为复数编写了一个类,你可以在下面看到它的代码;假设A和B是复数,我的问题是当我编写代码时:

cout << A + B; //它给了我一个错误

但是当我将A + B分配给类Complex的实例时,比如C,它可以正常工作.我的意思是:

复数C = A + B << endl; cout << C; //正常工作

我真的很困惑为什么我不能使用A + B作为<<运算符的右操作数.任何想法我怎么能直接c + A +？在此先感谢您的帮助.这是我到目前为止所提出的:

   #include <iostream>
   using namespace std;

class Complex {
     private:
        double real;
        double image;
     public:

    Complex(double r, double i){ real=r ; image=i;}

    int GetReal(){ return real;}
    int GetImage(){return image;}



    //overload complex + complex
    friend Complex operator+(const Complex &c1,const Complex &c2) ;
    //overload complex + double
    friend Complex operator+(const Complex &c,double Number) ;
    //overload double + complex
    friend Complex operator+(double Number,const Complex &c) ;

    //overload complex * complex
    friend Complex operator*(const Complex &c1, const Complex &c2);
    //overload complex * double
    friend Complex operator*(const Complex &c, double Number);
    //overload double * complex
    friend Complex operator*(double Number, const Complex &c);

    //overloading output operator
    friend ostream& operator<< (ostream &out, Complex &c);
 };
Complex operator+(const Complex &c1,const Complex &c2){
     return Complex(c1.real + c2.real,c1.image + c2.image);}

Complex operator+(const Complex &c,double Number){
     return Complex(c.real + Number , c.image);}

Complex operator+(double Number,const Complex &c){
     return Complex(Number + c.real,c.image);}

 //(a + bi) * (c + di) = ((ac-bd) + (ad+bc)i)
Complex operator*(const Complex &c1, const Complex &c2){
     return Complex(c1.real*c2.real-c1.image*c2.image,c1.real*c2.image+c1.image*c2.real);}

Complex operator*(const Complex &c, double Number){
     return Complex(c.real*Number,c.image*Number);}

Complex operator*(double Number, const Complex &c){
     return Complex(Number*c.real,Number*c.image);}

ostream& operator<< (ostream &out, Complex &c){
     if( c.image>0){

          out << c.real << "+ " <<
                c.image << "i";}
     else if (c.image==0){
          out<<c.real;
       }
     else { out<< c.real<<"- "<<
             c.image<< "i";}

     return out;}

int main(){

Complex A(1,2);
Complex B(3,4);

cout<<"A is: "<<A<<endl;
cout<<"B is: "<<B<<endl;
Complex c=A+B;
cout<<c<<endl;  //works correctly
cout<<A+B<<endl;  // gives an Error ?!


}

Answer 1

A+B是一个右值因为你operator+(正确)按价值返回.您不能将非常量左值引用绑定到右值.您需要更改运算符以获取const引用:

friend ostream& operator<< (ostream& out, const Complex& c);
                                          ^^^^^