https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90370
--- Comment #5 from Florian Weimer <fw at gcc dot gnu.org> --- (In reply to Florian Weimer from comment #4) > (In reply to Jonathan Wakely from comment #3) > > The issue is basically that the C++ Standard Library defines two categories > > for error numbers known to the implementation: "generic" and "system", where > > the former is for the POSIX errno values, and the latter is for other error > > numbers used by the OS for other kinds of errors that aren't covered by a > > POSIX errno macro (which might be other non-standard EBLAH macros that the > > OS adds to the POSIX ones, or some totally different error numbers used by > > the OS, e.g. Windows has its own error numbers unrelated to errno). The > > question is which category zero belongs to. > > This is really confusing for native POSIX systems because the generic/system > terminology appears to be swapped for them. This is also reflected in the > standard: > > <http://eel.is/c++draft/syserr.errcat.objects#4> > > And in the documentation: > > <https://en.cppreference.com/w/cpp/error/system_category> > > With this observation in mind, I reach this conclusion: > > For a native POSIX system, no translation of errno values is needed. That > suggests to me that all int values (the ev argument) correspond to a POSIX > errno value, and therefore all error conditions crated by > default_error_condition should be of the system_category category. Sorry, I meant generic_category on the last line (which really should be called posix_category or perhaps errno_category, based on the required behavior of default_error_condition). Why do I consider generic/system terminology swapped? A system error for GNU/Linux is a POSIX error because the that's the kind of error numbers the operating system uses. If the application uses non-POSIX errors that are unlikely (or impossible, in the case of Linux on most architectures) to occur as operating system errors for different error conditions, I would call that a “generic error” as in “not a system error”. However, I do not think that there is an debate that an ERANGE error needs to be of generic_category according to the specification, even though it is clearly a system error from the GNU/Linux point of view. If we say that all int error values are of generic_category, without further translation, I think this mostly resolves this confusion.
