C++ IOStream 运算符过载错误

Question

我遇到了一个错误，我似乎无法在我需要编写并最终适应更复杂的代码的基本程序中弄清楚。

Wordnum.cpp:10:67: error: ‘std::ostream& Wordnum::operator<<(std::ostream&, const Wordnum&)’ must take exactly one argument

Wordnum.cpp:14:61: error: ‘std::ostream& Wordnum::operator>>(std::istream&, Wordnum&)’ must take exactly one argument

这是我的两个错误，这是我的三个文件。

主.cpp

#include <cstdlib>
#include <iostream>

#include "Wordnum.h"

using namespace std;

int main(int argc, char** argv) {

    float n1, n2;
    char op;

    while (cin >> n1 >> op >> n2) {
        Wordnum a(n1), b(n2);
        switch (op) {
            case '+': cout << a + b << endl; break;
        }
    }

    return 0;
}

字数.h

#ifndef WORDNUM_H
#define WORDNUM_H

#include <iostream>

class Wordnum {
public:
    Wordnum(int n);     // CONSTRUCTOR

    friend Wordnum operator+ (const Wordnum& n1, const Wordnum& n2) 
        { return Wordnum(n1.value_ + n2.value_); }
    friend Wordnum operator- (const Wordnum& n1, const Wordnum& n2) 
        { return Wordnum(n1.value_ - n2.value_); }
    friend Wordnum operator* (const Wordnum& n1, const Wordnum& n2) 
        { return Wordnum(n1.value_ * n2.value_); }
    friend Wordnum operator/ (const Wordnum& n1, const Wordnum& n2) 
        { return Wordnum(n1.value_ / n2.value_); }

    friend std::ostream& operator<< (std::ostream&, const Wordnum& n);
    friend std::istream& operator>> (std::istream&, Wordnum& n);

private:
    int value_;
};

#endif  /* WORDNUM_H */

字数.cpp

#include "Wordnum.h"

#include <iostream>


Wordnum::Wordnum(int n) {
    value_ = n;
}

std::ostream& Wordnum::operator<< (std::ostream&, const Wordnum& n) {
    return 0;
}

std::ostream& Wordnum::operator>> (std::istream&, Wordnum& n) {
    return 0;
}

Answer 1

你已经声明为朋友 function 但通过使用WordNum::在WordNum.cpp中定义为 Wordnum 的成员，它应该是：

std::ostream& operator<< (std::ostream &os, const Wordnum& n) {
  return os;
}

std::istream& operator>> (std::istream &is, Wordnum& n) {
   return is;
}