操作符重载“+”复杂/双 [英] operator overloading "+" for types complex/double

问题描述

我只把有用的信息放在Complex.cpp中。

I put only the useful information in Complex.cpp.

这里是我的问题：我做了类复杂，这意味着它可以复杂计算。
在 + 运算符中我想启用复杂+双，但我只能在 main.cpp 。当我使用双变量+复合体时有一个错误。这是为什么？我可以修复吗？

Here is my problem: I made the class complex which means it can calculate in complex. In the + operator I want to enable complex + double, but I can only use complex + double in main.cpp. When I use a double variable + complex there is an error. Why is that? Can I fix it?

#ifndef COMPLEX_H
#define COMPLEX_H
using namespace std;
class Complex
{
public:
    Complex( double = 0.0, double = 0.0 ); // constructor
    Complex operator+( const Complex & ) const; // addition
    Complex operator-( const Complex & ) const; // subtraction
    Complex operator*( const Complex & ) const; // mul
    bool operator==( const Complex & ) const;
    bool operator!=( const Complex & ) const;
    friend ostream &operator<<( ostream & , const Complex& ); 
    friend istream &operator>>( istream & , Complex& );
    Complex operator+( const double & ) const;
    //Complex &operator+( const double & ) const;
    void print() const; // output
private:
    double real; // real part
    double imaginary; // imaginary part
}; // end class Complex

#endif

Complex.cpp

Complex.cpp

Complex Complex::operator+( const Complex &operand2 ) const
{
    return Complex( real + operand2.real,imaginary + operand2.imaginary );
} // end function operator+

Complex Complex::operator+(const double &operand2) const
{
    return Complex( real + operand2 , this->imaginary );
}

main.cpp

main.cpp

int main()
{
Complex x;
Complex y( 4.3, 8.2 );
Complex z( 3.3, 1.1 );

    double ss = 5;
    x = z + ss;
    x = ss + z;//this syntax is illegal 

推荐答案

为了允许你的类显示为右手操作数，操作符需要是非成员。因为（在这种情况下）它需要访问私有成员，所以它必须是一个朋友：

In order to allow your class to appear as the right hand operand, the operator needs to be a non-member. Since (in this case) it needs access to the private members, it will have to be a friend:

class Complex {
    // ...
    friend Complex operator+(double lhs, const Complex & rhs);
};

Complex operator+(double lhs, const Complex & rhs) {
    return Complex(lhs+rhs.real, rhs.imaginary);
}

或者，因为你已经有一个成员采用反向的参数，和添加是对称的，你可以定义一个非成员，非朋友函数：

Alternatively, as you already have a member taking the arguments the other way round, and addition is symmetric, you could define a non-member, non-friend function:

Complex operator+(double lhs, const Complex& rhs) {
    return rhs + lhs;
}

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