C++好友运营商+超载

发布于 2024-10-16 10:08:12 字数 551 浏览 7 评论 0原文

我对友元运算符重载感到困惑。如果我在头文件中编写友元运算符重载函数，那么没有问题，但是一旦将函数移动到类文件中，就会出现以下错误。我用谷歌搜索了一些示例，它们都将函数写入了头文件中。我做错了什么？谢谢。

...: error: expected ‘,’ or ‘...’ before ‘&’ token
...: error: ISO C++ forbids declaration of ‘statisticain’ with no type
...: error: ‘main_savitch_2C::statistician operator+(int)’ must have an argument of class or enumerated type


// a.h
class A
{
    public:
        friend A operator + (const A &a1, const A &a2);
};

// a.cpp
#include "a.h"
A operator + (const A &a1, const A &a2)
{
    //
}

原文

I'm confused about friend operator overloading. It has no problem if I write the friend operator overloading function within the header file, but it gives me the following errors once I moved the function to class file. I googled some samples and they all written the function in the header file. What did I do wrong? Thanks.

...: error: expected ‘,’ or ‘...’ before ‘&’ token
...: error: ISO C++ forbids declaration of ‘statisticain’ with no type
...: error: ‘main_savitch_2C::statistician operator+(int)’ must have an argument of class or enumerated type


// a.h
class A
{
    public:
        friend A operator + (const A &a1, const A &a2);
};

// a.cpp
#include "a.h"
A operator + (const A &a1, const A &a2)
{
    //
}

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情徒 2024-10-23 10:08:12

从您收到的错误消息来看：

ISO C++ forbids declaration of ‘statisticain’ with no type

我认为您通过颠倒最后两个字母拼错了“statistician”（请注意，您有“statisticain”而不是“statistician”。）

这应该与是否 operator+ 无关 在头文件或 .cpp 文件中实现。

From the error message you're getting:

ISO C++ forbids declaration of ‘statisticain’ with no type

I think that you misspelled "statistician" by reversing the last two letters (note that you have "statisticain" instead of "statistician.")

This should have nothing to do with whether operator+ is implemented in the header or the .cpp file.

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不必你懂 2024-10-23 10:08:12

我同意之前的回答。另外，如果我可能会问，当参数和返回类型都属于同一类时，为什么要让函数成为朋友呢？为什么不将其设为成员，以便第一个参数由 this 运算符隐式传递？

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乱世争霸 2024-10-23 10:08:12

将两个参数版本移出类声明。或者只使用一个参数和 this 指针。

这是一个简短的现实世界示例。

//complexnumber.h 
    class ComplexNumber
    {
        float _r;
        float _i;

        friend ComplexNumber operator+(const ComplexNumber&, const ComplexNumber&);

        public:
            ComplexNumber(float real, float img):_r(real),_i(img) {}
            ComplexNumber& operator + (const ComplexNumber &other);
    };

    ComplexNumber operator+(const ComplexNumber &c1, const ComplexNumber& c2);


//complexnumber.h 
    ComplexNumber operator+(const ComplexNumber &c1, const ComplexNumber& c2)
    {
        return ComplexNumber(c1._r+c2._r, c1._i+c2._i);
    }


    // static
    ComplexNumber& ComplexNumber::operator + (const ComplexNumber &other)
    {
        this->_r = this->_r + other._r;
        this->_i = this->_i + other._i;

        return *this;

    }

Move the two param version out of the class declaration. Or just use one param and the this pointer.

Here's an abbreviated real world example.

//complexnumber.h 
    class ComplexNumber
    {
        float _r;
        float _i;

        friend ComplexNumber operator+(const ComplexNumber&, const ComplexNumber&);

        public:
            ComplexNumber(float real, float img):_r(real),_i(img) {}
            ComplexNumber& operator + (const ComplexNumber &other);
    };

    ComplexNumber operator+(const ComplexNumber &c1, const ComplexNumber& c2);


//complexnumber.h 
    ComplexNumber operator+(const ComplexNumber &c1, const ComplexNumber& c2)
    {
        return ComplexNumber(c1._r+c2._r, c1._i+c2._i);
    }


    // static
    ComplexNumber& ComplexNumber::operator + (const ComplexNumber &other)
    {
        this->_r = this->_r + other._r;
        this->_i = this->_i + other._i;

        return *this;

    }

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