http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51437
--- Comment #8 from Rich Felker <bugdal at aerifal dot cx> 2012-02-19 05:47:18 UTC --- 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. >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. 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.
