http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51437
--- Comment #9 from Josh Triplett <josh at joshtriplett dot org> 2012-02-19 06:29:27 UTC --- (In reply to comment #8) > You really do want to flag both definition and usage. For instance, there's > plenty of buggy software (especially GNU software like binutils) using __pid_t > and similar when it should be using pid_t, etc. In the case of identifiers containing __ or starting with _[A-Z], that does hold true; I hadn't considered programs using internal identifiers when corresponding public identifiers exist. (Ideally the headers could have avoided exposing those internal identifiers to user programs in the first place, but I don't know any sensible way to implement that.) However, note that the standards also reserve various other classes of names, such as types ending in _t, for which GCC should only flag definitions, not uses. Only system headers should define new _t types, but user code can *use* types like time_t or pid_t without warning. (Some of the other reserved identifier categories, such as E[A-Z0-9].*, is[a-z].*, to[a-z].*, and mem[a-z].* should go under some separate, more pedantic warning option.) > From an undefined behavior standpoint, defining a name in the reserved > namespace is no worse than using a name in the referred namespace assuming the > implementation has defined it. Both are incorrect C usage and both should be > flagged. True. I had mostly wanted to avoid generating hundreds of warnings for the same identifier. However, that seems better than missing cases like the __pid_t you mentioned above. > My heuristic about -isystem would prevent flagging usage of reserved names > resulting from implementations of system headers - for instance, if a macro in > a system header used __uint32_t because it needs to avoid making uint32_t > visible. Right. That seems like the same heuristic documented at http://gcc.gnu.org/onlinedocs/cpp/System-Headers.html that I referenced in comment 7: "Macros defined in a system header are immune to a few warnings wherever they are expanded."
