Global function definition in header file - how to avoid duplicated symbol linkage error

Question

I have the following code in a header only file.

#pragma once

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

std::ostr         


        

Answer 1

Use the inline keyword.

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