Global function definition in header file - how to avoid duplicated symbol linkage error
Use the inline
keyword.
inline std::ostream& operator<< (std::ostream& o, const error_code& e) {
return o << "[" << e.hi << "," << e.lo << "]";
}
Either make the function inline
:
inline std::ostream& operator<< (std::ostream& o, const error_code& e) {
return o << "[" << e.hi << "," << e.lo << "]";
}
or make it a template function:
template<class Ch, class Tr>
std::basic_ostream<Ch,Tr>& operator<< (std::basic_ostream<Ch,Tr>& o,
const error_code& e) {
return o << "[" << e.hi << "," << e.lo << "]";
}
You can make the function static
. It specifies internal linkage, so the linker won't care if the function is already defined in other translation units.
Or, as already mentioned, you can make it inline
. It still has external linkage, but the standard allows external inline functions to have a definition in multiple translation units.