朋友运营商的用法 [英] usage of friend operators

问题描述

您好，


我有矢量模板的代码。但是我遇到了问题。

Vector.hpp文件的开头如下：


template< class V，class I = int，class S = FullArray< V> >

类Vector：public Array< V，I，S>


{...


// Array和FullArray是已经构建的一些其他模板。

//这个Vector模板的目标是简单地为vector

//类创建一个带有一些数值功能的类，比如vector vector。


//这不是我原来的代码，但据我所知+运算符

//重载以使Vector类具有一些功能：

//添加两个相同维度的向量。并且通过将标量添加到向量的每个维度来添加向量和标量

//。这是在

//中完成以下方式：


//返回元素的总和

//运算符

矢量< V，I，S>& operator =（const Vector< V，I，S>& source）;


Vector< V，I，S> operator - （）const; //一元减去


//为每个元素添加v

friend Vector< V，I，S> operator +（const Vector< V，I，S>& v，const V& a）;


朋友矢量< V，I，S> operator +（const V& a，const Vector< V，I，S>& v）;


//添加元素

Vector< V ，我，S> operator +（const Vector< V，I，S>& v）const;


//但是当我尝试在主函数中使用此模板时，我得到以下内容：


[警告]朋友声明`Vector< ; V，I，S> operator +（const Vector< V，I，S>&，const V&）''声明一个非模板函数


[警告]（如果这不是你想要的，确保函数模板已经声明并在函数名称之后添加<>）-Wno-non-template-friend禁用此警告



我不要我不知道该怎么做。我真的很感激帮助。谢谢。

解决方案

此代码：

//为每个元素添加v

friend vector< V，I，S> operator +（const Vector< V，I，S>& v，const V& a）;

不正确。矢量< V，I，S>类是本身，它是第一个参数，意味着它位于+运算符的左侧。当Vector位于+运算符的左侧时，编译器将提供此指针指向函数，因此您不需要Vector作为第一个参数。


这应该不是朋友。它应该是一个成员函数：

展开 | 选择 | Wrap | 行号

您好，


我理解替换背后的想法：


" friend Vector< V，I，S> operator +（const Vector< V，I，S>& v，const V& a）;"


，Vector< V，I，S> operator +（const V& a）;"


但是，一旦我这样做了。我仍然收到错误：


朋友矢量< V，I，S> operator +（const V& a，const Vector< V，I，S>& v）;


[警告]朋友声明`Vector< V，I，S> operator +（const V&，const Vector< V，I，S>&）''声明一个非模板函数


我该怎样处理这个？您是否建议将其替换为


Vector< V，I，S> operator +（const V& a）;


谢谢

friend Vector< V，我，S> operator +（const V& a，const Vector< V，I，S>& v）;

为了成为朋友，它必须是一个已经写好的函数。

展开 | 选择 | Wrap | 行号

Hello,

I have code for a vector template. However I am having problems with it.
Vector.hpp file starts like this:

template <class V, class I=int, class S=FullArray<V> >
class Vector: public Array<V, I, S>

{...

//Array and FullArray are some other templates that are already constructed.
//The goal of this Vector template is to simply create a template for vector
//classes with some numerical capabilities such as vector addition.

//This is not originally my code, however as far as I can understand + operator
//is overloaded to enable the Vector class some functionalities:
//Adding two vectors of same dimension. And also adding a vector and a scalar
//by adding the scalar to every dimension of the vector. This is beeing done in
//the following way:

// Return the sum of the elements
// Operators
Vector<V, I, S>& operator = (const Vector<V, I, S>& source);

Vector<V, I, S> operator - () const; // Unary minus

// Add v to every element
friend Vector<V, I, S> operator + (const Vector<V, I, S>& v, const V& a);

friend Vector<V, I, S> operator + (const V& a, const Vector<V, I, S>& v);

// Add the elements
Vector<V, I, S> operator + (const Vector<V, I, S>& v) const;

//However when I try to use this template in a main function I get the following:

[Warning] friend declaration `Vector<V, I, S> operator+(const Vector<V, I, S>&, const V&)'' declares a non-template function

[Warning] (if this is not what you intended, make sure the function template has already been declared and add <> after the function name here) -Wno-non-template-friend disables this warning


I don''t know what to do here. I would really appreciate help. Thanks.

解决方案

This code:

// Add v to every element
friend Vector<V, I, S> operator + (const Vector<V, I, S>& v, const V& a);

isn''t correct. Vector<V,I,S> is the class itself and it is the first argument meaning it is on the left of the + operator. When a Vector is on the left of the + operator, the compiler will supply the this pointer to the function so you don''t need a Vector as the first argument.

This should not be a friend. It should be a member function:

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Hello,

I understand the idea behind replacing:

"friend Vector<V, I, S> operator + (const Vector<V, I, S>& v, const V& a);"

with Vector<V, I, S> operator + (const V& a);"

However, once I do this. I am still getting an error for:

friend Vector<V, I, S> operator + (const V& a, const Vector<V, I, S>& v);

[Warning] friend declaration `Vector<V, I, S> operator+(const V&, const Vector<V, I, S>&)'' declares a non-template function

How can I take care of this? Are you suggesting to replace this with

Vector<V, I, S> operator + (const V& a);

Thanks

friend Vector<V, I, S> operator + (const V& a, const Vector<V, I, S>& v);

For this to be a friend, it has to be a function that is already written.

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