https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86491
Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org Status|NEW |ASSIGNED --- Comment #12 from Jonathan Wakely <redi at gcc dot gnu.org> --- In C++98 entities in an anonymous namespace did not have internal linkage, that was changed for C++11. But they can still cause ODR violations. So the diagnostic talks about anonymous namespaces because that's what causes the potential for ODR violations, not linkage. THat was changed for C++11 so that anonymous namespacs give internal linkage, and things with internal linkage can now be used in templates, so the existing warning was extended to cover those cases, but without rewording it. In C++98 the testcase in comment 7 is simply ill-formed: tM.C:3:15: error: ‘& d’ is not a valid template argument of type ‘int*’ in C++98 because ‘d’ does not have external linkage But if you change it to use an anonymous namespace it's valid in C++98: # 1 "t1.H" template < int *_C_OBJ_> struct NT{}; # 2 "tM.C" namespace { int d; } struct D : NT<&d> {}; This is valid in C++98 because 'd' doesn't have internal linkage (it's just different in every translation unit), but it is still a potential ODR violation, so there's a warning: tM.C:3:8: warning: ‘D’ has a base ‘NT<(& {anonymous}::d)>’ whose type uses the anonymous namespace [-Wsubobject-linkage] Maybe for C++98 it should always say "anonymous namespace" since that's the only way to trigger the warning, and for C++11 and later it should say internal linkage, since that is true for names declared 'static' or in an anon namespace. That seems like an easy change.