Question

我在使用C ++重载我的流提取运算符时遇到了一些麻烦。我不确定为什么我会收到这些编译错误，因为我认为我做得对...这是我的代码：

Complex.h

#ifndef COMPLEX_H
#define COMPLEX_H

class Complex
{
    //friend ostream &operator<<(ostream &output, const Complex &complexObj) const;
     // note at bottom regarding friend function
public:
    Complex(double = 0.0, double = 0.0); // constructor
    Complex operator+(const Complex &) const; // addition
    Complex operator-(const Complex &) const; // subtraction
    void print() const; // output
private:
    double real; // real part
    double imaginary; // imaginary part
};

#endif

Complex.cpp

#include <iostream>
#include "Complex.h" 
using namespace std;

// Constructor
Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart)
{
}

// addition operator
Complex Complex::operator+(const Complex &operand2) const
{
    return Complex(real + operand2.real, imaginary + operand2.imaginary);
}

// subtraction operator
Complex Complex::operator-(const Complex &operand2) const
{
    return Complex(real - operand2.real, imaginary - operand2.imaginary);
}

// Overload << operator
ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const 
{
    cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')';
    return output;  // returning output allows chaining
}

// display a Complex object in the form: (a, b)
void Complex::print() const
{
    cout << '(' << real << ", " << imaginary << ')';
}

的main.cpp

#include <iostream>
#include "Complex.h"
using namespace std;
int main()
{
    Complex x;
    Complex y(4.3, 8.2);
    Complex z(3.3, 1.1);

    cout << "x: ";
    x.print();
    cout << "\ny: ";
    y.print();
    cout << "\nz: ";
    z.print();

    x = y + z;
    cout << "\n\nx = y + z: " << endl;
    x.print();
    cout << " = ";
    y.print();
    cout << " + ";
    z.print();

    x = y - z;
    cout << "\n\nx = y - z: " << endl;
    x.print();
    cout << " = ";
    y.print();
    cout << " - ";
    z.print();
    cout << endl;
}

编译错误：

complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex'
complex.h(5) : see declaration of 'Complex'
complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions
complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex'
complex.h(13) : see declaration of 'Complex::real'
complex.h(5) : see declaration of 'Complex'
complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex'
complex.h(14) : see declaration of 'Complex::imaginary'
complex.h(5) : see declaration of 'Complex'

谢谢！

编辑：

I wasn't sure about declaring the friend function in the header file or not.  When I do, I get these errors:
c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2433: 'ostream' : 'friend' not permitted on data declarations
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2061: syntax error : identifier 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2805: binary 'operator <<' has too few parameters
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2086: 'int ostream' : redefinition
1>        c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : see declaration of 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2872: 'ostream' : ambiguous symbol
1>        could be 'c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : int ostream'
1>        or       'c:\program files\microsoft visual studio 9.0\vc\include\iosfwd(708) : std::ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2065: 'output' : undeclared identifier
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(23) : error C2059: syntax error : 'const'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(24) : error C2143: syntax error : missing ';' before '{'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.cpp(24) : error C2447: '{' : missing function header (old-style formal list?)
1>Generating Code...
1>Compiling...
1>main.cpp
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2143: syntax error : missing ';' before '&'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2433: 'ostream' : 'friend' not permitted on data declarations
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2061: syntax error : identifier 'ostream'
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\documents and settings\wongj\my documents\visual studio 2008\projects\c3_hw\c3_hw4\complex.h(6) : error C2805: binary 'operator <<' has too few parameters

Answer 1

标题中的注释掉的声明几乎是正确的。因为它是朋友，所以它不是成员，因此不能是const，所以它应该是：

friend std::ostream &operator<<(std::ostream &output, const Complex &complexObj);

另请注意，您需要将ostream限定为std::ostream，因为您不应在头文件中使用using namespace std;（您实际上不需要在任何地方使用它;它通常是当你想使用标准库中的东西时，最好只写出std::。

同样，在源文件中，由于它不是成员函数，因此不要在操作符定义前加上类名称，它应该是：

std::ostream &operator<<(std::ostream &output, const Complex &complexObj)

Answer 2

如果您希望客户端代码能够访问运营商＆lt;＆lt;重载，添加

ostream & operator<<(ostream &output, const Complex &complexObj) const

到您的类头文件。

另一方面，如果您只想要客户端代码调用print（），请删除

Complex::

从实现文件中的运算符定义确定范围。

C ++帮助中的运算符重载流提取运算符

2 个答案: