c++ - 如何解决 operator>> 重载错误(不匹配 'operator>>' )

Question

我查看了有关此的其他主题并尝试查看是否可以找到我的错误，但我无法找到解决错误的方法。

我的错误:

no match for ‘operator>>’ (operand types are ‘std::istream {aka std::basic_istream<char>}’ and ‘Polynomial()’)
cin >> p3;

主要内容:

// includes, namespace, etc...

int main()
{
    Polynomial p3();

    // Prompts user and assigns degrees and coefficients
    cout << "Enter the degree followed by the coefficients: ";
    cin >> p3;

    // other coding
 }

运算符的头文件定义>>:

class Polynomial 
{
      private:
          double *coefs;
          int degree;
      public:
          // constructors, setters/getters, functions
          friend std::istream &operator >>(std::istream &in, Polynomial &poly);
};

执行文件:

Polynomial::Polynomial() // default constructor
{
    degree = 0;
    coefs = new double[1];
    coefs[0] = 0.0;
}

std::istream &operator >>(std::istream &in, Polynomial &poly) ////!!!!!!
{
    in >> poly.degree;

    delete[] poly.coefs; // deallocate memory
    poly.coefs = new double[poly.degree + 1]; // create new coefficient array

    for(int i = 0; i <= poly.degree; i++) // assigns values into array
    {
        in >> poly.coefs[i];
    }

    return in;
}

Answer 1

Polynomial p3(); 是函数声明，而不是变量定义(如您所料)。它声明了一个名为 p3 的函数，该函数返回 Polynomial 并且没有参数。还要注意错误消息，它说操作数类型是 Polynomial()，这是一个函数。

改成

Polynomial p3;

或

Polynomial p3{}; // since C++11