在头文件中具有全局函数定义，并避免重复的符号链接错误 [英] Have global function definition in header file, and avoid duplicated symbol linkage error

问题描述

我在头文件中有以下代码。

I have the following code in a header only file.

#pragma once

class error_code {
public:
    unsigned __int64 hi;
    unsigned __int64 lo;    
};

std::ostream& operator<< (std::ostream& o, const error_code& e) {
    return o << "[" << e.hi << "," << e.lo << "]";
}

我得到链接错误，当项目中有2个cpp包含此标题文件

I get linkage error, when there are 2 cpp in the project include this header file.

错误LNK2005：class error_code
__cdecl operator |（class error_code const&，class ViTrox :: error_code const
&）（?? U @@ YA？AVerror_code @ 0 @ ABV10 @ 0 @ Z）
已在xxx.obj中定义

error LNK2005: "class error_code __cdecl operator|(class error_code const &,class ViTrox::error_code const &)" (??U@@YA?AVerror_code@0@ABV10@0@Z) already defined in xxx.obj

我知道我可以解决这个问题，如果我把操作符< 的定义移动到cpp文件或DLL文件。

I know I can resolve this problem, if I move the definition of operator<< to a cpp file, or to a DLL file.

但是，我只想将它们放在 SINGLE 头文件中。有什么技术可以实现吗？或者必须将定义分隔到另一个文件？

However, I just would like to have them in a SINGLE header file. Is there any technique to achieve so? Or must I separate the definition to another file?

推荐答案

使用 inline 关键字。

inline std::ostream& operator<< (std::ostream& o, const error_code& e) {
    return o << "[" << e.hi << "," << e.lo << "]";
}

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