C++ IOStream 運算符過載錯誤

Question

我遇到了一個錯誤，我似乎無法在我需要編寫並最終適應更復雜的代碼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

這是我的兩個錯誤，這是我的三個文件。

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;
}

字數.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 */

字數.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

你已經聲明為朋友 function 但通過使用WordNum::在WordNum.cpp中定義為 Wordnum 的成員，它應該是：

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

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