C ++ ostream重载不起作用(C++ ostream overloading not working)

C ++ ostream重载不起作用(C++ ostream overloading not working)

编辑：

经过一些评论，现在这是我的代码，遵循此链接。（更好，但我仍然有错误）

离婚：

ostream& operator<<(ostream& out, Device& v) { out << "Device " << v.get_name() << " Has an ID of: " << v.get_id(); return out; }

内部设备类：

friend ostream& operator<<(ostream& os, const Device& v);

我的调用:(设备类型为Node，val返回设备）

cout << device->val << endl;

我的错误：

错误LNK2019未解析的外部符号“class std :: basic_ostream> std :: char_traits>＆__ cdecl operator <<（class std :: basic_ostream>＆，class Device const＆）”（?? 6 @ YAAAV？$ basic_ostream @ DU？$ char_traits @ D @ std @@@ std @@ AAV01 @ ABVDevice @@@ Z）在函数“void __cdecl print_devices（class Node *）”中引用（？print_devices @@ YAXPAV？$ Node @ VDevice @@@@@ Z）

原版的：

我被告知，重载运算符是这样的：

ostream& Device::operator<<(ostream &out) { out << "Device " << this->name << " Has an ID of: " << this->id; return out; }

但是在尝试使用这种重载时 - （设备是类型设备）

cout << device << endl;

它标志着阅读并说 -

错误C2679二进制'<<'：找不到哪个运算符带有'Device'类型的右手操作数（或者没有可接受的转换）

为什么我会收到此错误，如何解决？ 我在网上看了，但找不到一个在课堂上工作的方法，只有这个：

朋友ostream＆operator <<（ostream＆out，Point＆cPoint）;

哪个对我也不起作用。

Edit:

After some comments, this is my code now, following THIS link.(Better, but I still have an error)

Out of everyhing:

ostream& operator<<(ostream& out, Device& v) { out << "Device " << v.get_name() << " Has an ID of: " << v.get_id(); return out; }

Inside Device class:

friend ostream& operator<<(ostream& os, const Device& v);

My call: (device is of type Node, and val returns the device)

cout << device->val << endl;

My error:

Error LNK2019 unresolved external symbol "class std::basic_ostream > std::char_traits > & __cdecl operator<<(class std::basic_ostream > &,class Device const &)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@ABVDevice@@@Z) referenced in function "void __cdecl print_devices(class Node *)" (?print_devices@@YAXPAV?$Node@VDevice@@@@@Z)

Original:

I was taught that overloading an operator is made like this:

ostream& Device::operator<<(ostream &out) { out << "Device " << this->name << " Has an ID of: " << this->id; return out; }

But when trying to use this overloading - (device is type Device)

cout << device << endl;

It marks in read and says -

Error C2679 binary '<<': no operator found which takes a right-hand operand of type 'Device' (or there is no acceptable conversion)

Why do I get this error, and how can I fix it? I looked online, but could not find a method that works inside the class, only this:

friend ostream& operator<< (ostream &out, Point &cPoint);

Which did not work for me as well.

最满意答案

您在Device类中声明的内容是

friend ostream& operator<<(ostream& os, const Device& v);

但你提供的实现是什么

ostream& operator<<(ostream& out, Device& v) { out << "Device " << v.get_name() << " Has an ID of: " << v.get_id(); return out; }

这不是一回事 ！ 你告诉编译器有一个friend函数，它引用了一个ostream和一个对const的const引用 - 但是你提供的const错过了Device前面的const 。

What you have declared inside your Device class is

friend ostream& operator<<(ostream& os, const Device& v);

but what you have provided the implementation for is

ostream& operator<<(ostream& out, Device& v) { out << "Device " << v.get_name() << " Has an ID of: " << v.get_id(); return out; }

which is not the same thing! You told the compiler there is a friend function which takes a reference to an ostream and a const reference to a Device - but the function you have provided misses the const in front of Device.