C++ IOStream操作符過載錯誤

Question

我遇到了一個錯誤，我似乎無法弄清楚我需要編寫的最基本的程序，並最終適應更復雜的一段代碼。

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 

這些是我的兩個錯誤，這裏是我的三個文件。

Main.cpp的

#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; 
} 

Wordnum.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 */ 

Wordnum.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

你已經聲明爲友元函數，而是通過使用WordNum::定義爲Wordnum成員WordNum.cpp應該改爲：

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

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