操作员<<过载

Operator << overloading

本文关键字：lt 过载 操作员      更新时间：2023-10-16

我正在处理我的项目，我想重载运算符<<，它应该在控制台上打印出我的对象。
对象称为"config"，在其模板类中，它有 4 个数组，分别称为attribute1、attribute2。attribute3和attribute4.

到目前为止，我已经尝试过这个：

#include "stdafx.h"
#include <string>
#include <iostream>
using namespace std;
template<typename T> class config
{
T *attribute1, *attribute2, *attribute3, *attribute4;
string attribName1, attribName2, attribName3, attribName4;
public:
config(void)
{
attribute1 = new T[3];
attribute2 = new T[3];
attribute3 = new T[3];
attribute4 = new T[3];
}   
~config(void)//destruktor
{
delete [] attribute1, attribute2, attribute3, attribute4;
}
//operatory
friend ostream& operator<<(ostream &out, const config<T> &c); 
};//class ends
template <typename T> ostream& operator<<(ostream &out, const config<T> &c)
{
for(int i=0;i<3;i++)
{
out<<c.attribute1[i]<<c.attribute2[i]<<c.attribute3[i]<<c.attribute2[i];
}
return out;
}

每当我尝试编译它时，它都会给出某种奇怪的错误，但我知道问题出在运算符上。

这是它给出的错误：

Error   1   error LNK2001: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class config<double> const &)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABV?$config@N@@@Z)    D:DocsVisual Studio 2010Projectsproject_v2.obj  project_v2

和：

Error   2   error LNK1120: 1 unresolved externals   D:DocsVisual Studio 2010Projectsproject_v2.exe  project_v2

并且未指定行或列。

这是解决问题的一种方法。

  1. 在定义config之前，先声明operator<<函数。为了声明函数，您必须转发声明类模板。

    template <typename T> class config;
template <typename T> std::ostream& operator<<(std::ostream &out,
const config<T> &c);

  2. 在类中，通过使用T作为模板参数使函数成为友元函数。

    friend ostream& operator<< <T>(ostream &out, const config &c);
// Notice  this            ^^^^
// This makes sure that operator<< <int> is not a friend of
// config<double>. Only operator<< <double> is a friend of
// config<double>

以下是包含这些更改的工作程序：

#include <string>
#include <iostream>
template <typename T> class config;
template <typename T> std::ostream& operator<<(std::ostream &out,
const config<T> &c);
template <typename T> class config
{
T *attribute1, *attribute2, *attribute3, *attribute4;
std::string attribName1, attribName2, attribName3, attribName4;
public:
config(void)
{
attribute1 = new T[3];
attribute2 = new T[3];
attribute3 = new T[3];
attribute4 = new T[3];
}   
~config(void)//destructor
{
delete [] attribute1;
delete [] attribute2;
delete [] attribute3;
delete [] attribute4;
}
//operator
friend std::ostream& operator<< <T>(std::ostream &out,
const config &c);
};
template <typename T> std::ostream& operator<<(std::ostream &out,
const config<T> &c)
{
for(int i=0;i<3;i++)
{
out << c.attribute1[i] << " "
<< c.attribute2[i] << " "
<< c.attribute3[i] << " "
<< c.attribute2[i] << std::endl;
}
return out;
}
int main()
{
config<double> x;
std::cout << x << std::endl;
}

输出：

0 0
0 0 0 0 0 0 0 0 0 0
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