c++ - 重载 I/O 流运算符和前/后递增/递减运算符错误？

Question

这是我在学习 C++ 的网站上找到的一段代码。我不知道如何调试程序，所以我无法弄清楚问题出在哪里。

#include <iostream>

using namespace std;
class Complex
{
int real;
int img;
public:
Complex()
{
    real = 0;
    img = 0;
}

Complex(int r, int i)
{
    real = r;
    img = i;
}

Complex& operator++();
Complex operator++(int);

friend Complex operator+(Complex &a, Complex &b);
friend ostream& operator<<(ostream &out, Complex &a);
friend istream& operator>>(istream &in, Complex &a);

void display()
{
    using namespace std;
    cout << real << " + " << img << endl;
}

};

Complex& Complex::operator++()
{
    ++real;
    ++img;
    return *this;
}

Complex Complex::operator++(int)
{
    Complex temp(*this);
    ++(*this);
    return temp;
}

Complex operator+(Complex &a, Complex &b)
{
    int x = a.real + b.real;
    int y = a.img + b.img;
    return Complex(x, y);
}
ostream& operator<<(ostream &out, Complex &a)
{
    using namespace std;
    out << a.real << " + " << a.img << endl;
    return out;
}

istream& operator>>(istream &in, Complex &a)
{
    using namespace std;
    cout << "Enter the real part" << endl;
    in >> a.real;
    cout << "Enter the imaginary part" << endl;
    in >> a.img;
    return in;
}

int main()
{
    Complex a;
    cin >> a;
    Complex b(11,8);
    cout << "a is :" << a << endl;
    cout << "b is :" << b << endl;
    Complex c = Complex(a + b);
    cout << "c is :" << c << endl;
    cout << c;
    cout << c++;
    cout << c;
    cout << ++c;
    cout << c;
}

编译器从我试图在 main() 中递增 Complex 实例的行给出错误。据我所知，一切都很好，但是 Code::Blocks 给出了这些错误:

1. error: cannot bind 'std::ostream {aka std::basic_ostream<char>}' lvalue to 'std::basic_ostream<char>&&'|

2. error: initializing argument 1 of 'std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&&, const _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Tp = Complex]|

现在这让我相信(重载的)I/O 运算符有一些应该遵循的特殊规则，以便与(重载的)递增/递减运算符一起使用。

问题:

1. 这是真的吗，还是我没有捕捉到的代码有问题？我是这个领域的初学者。

2. 重载输出/输入运算符和递增(post,pre)/递减运算符是否有一些额外的规则可以一起使用？

P.S.:请原谅我的英语不好......谢谢

Answer 1

我没有遇到与您相同的错误，但这肯定是一个问题:

ostream& operator<<(ostream &out, Complex &a);
Complex operator++(int);
cout << c++;

您已声明 operator<<采取它的Complex通过对非常量的引用的参数，然后尝试将临时绑定(bind)到该引用。临时对象不能绑定(bind)到非常量引用。

解决这个问题的简单方法是声明您的运算符(operator)接受 a通过 reference-to-const 以便右值可以绑定(bind)到它:

ostream& operator<<(ostream &out, const Complex &a);