c++用成员函数和友元函数实现复数的加减操作，产生了二义性，麻烦各位大哥大姐解答一下，感激不尽

我想在一个程序中用友元函数和类的成员函数实现复数的加减操作，
类中这样定义：

main函数中用这几句调用的话存在二义性：

c3=c1+c2;这一句就不知道到底该调用成员函数还是调用友元函数，但是重载的话只有参数类型和参数个数不同，就应该没问题的，这里该怎么解决呢？
麻烦各位大哥大姐了；下面是程序的代码，

#include

class Complex
{
public:
Complex(double r=0.0,double i=0.0):real(r),imag(i){}
Complex operator+ (const Complex &c2)const;
Complex operator- (const Complex &c2)const;

    friend Complex operator+(const Complex &c1,const Complex &c2);
    friend Complex operator-(const Complex &c1,const Complex &c2);


    friend ostream &operator<< (ostream &out,const Complex &c);
    void display()const;
private:
    double real;
    double imag;            

} ;

Complex Complex::operator+ (const Complex &c2)const
{
return Complex(real+c2.real,imag+c2.imag);
}
Complex Complex::operator- (const Complex &c2)const
{
return Complex(real-c2.real,imag-c2.imag);
}

void Complex::display()const
{
cout<<"("<<real<<","<<imag<<")"<<endl;
}

Complex operator+(const Complex &c1,const Complex &c2)
{
return Complex(c1.real+c2.real,c1.imag+c2.imag);
}
Complex operator-(const Complex &c1,const Complex &c2)
{
return Complex(c1.real-c2.real,c1.imag-c2.imag);
}
ostream &operator<< (ostream &out,const Complex &c)
{
out<<"("<<c.real<<","<<c.imag<<")"<<endl;
return out;
}

int main()
{
Complex c1(5,4),c2(2,10),c3;
c1.display();
c2.display();
c3.display();

c3=c1+c2;
c3.display();
cout<<c3;

c3=c3-c1;
c3.display();
cout<<c3;

return 0;

}

你在函数里写个输出就能看出优先级了，具体我也没试过，无法给出正确答案

 c3=c1+c2;//对象+对象
 用成员函数 Complex operator+ (const Complex &c2)const;

 c3=4+c2; //数+对象
 用友元函数
 friend Complex operator+ (double r, const Complex &c2);

谢谢两位哈，太感谢了，我用这种方式消除了二义性；
真正写代码的时候肯定不会这么用的，我只是想知道该怎么消除二义性。谢谢两位哈

#include
using namespace std;

class Complex
{
public:
Complex(double r = 0.0, double i = 0.0) :real(r), imag(i){}
//Complex operator+ (const Complex &c2)const;
//Complex operator- (const Complex &c2)const;
friend Complex operator+(const Complex &c1, const Complex &c2);
friend Complex operator-(const Complex &c1, const Complex &c2);

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

private:
double real;
double imag;
};
//Complex Complex::operator+ (const Complex &c2)const
//{
// return Complex(real + c2.real, imag + c2.imag);
//}
//Complex Complex::operator- (const Complex &c2)const
//{
// return Complex(real - c2.real, imag - c2.imag);
//}
void Complex::display()const
{
cout << "(" << real << "," << imag << ")" << endl;
}
Complex operator+(const Complex &c1, const Complex &c2)
{
return Complex(c1.real + c2.real, c1.imag + c2.imag);
}
Complex operator-(const Complex &c1, const Complex &c2)
{
return Complex(c1.real - c2.real, c1.imag - c2.imag);
}
ostream &operator<< (ostream &out, const Complex &c)
{
out << "(" << c.real << "," << c.imag << ")" << endl;
return out;
}

int main()
{
Complex c1(5, 4), c2(2, 10), c3;
c1.display();
c2.display();
c3.display();
c3 = c1 + c2;
c3.display();
cout << c3;

c3 = c3 - c1;
c3.display();
cout << c3;

return 0;

}

你这样写必然产生二义性...弄清楚什么事表像，什么事本质...