Eric Blake wrote: > So if I understand correctly, you are trading one set of portability > problems (the AIX workaround guesses wrong for char and short) for another > (alignof() must not be used to initialize an enumerator, but can be used > in all other contexts). Shouldn't this at least be documented in the > alignof.h header?
Good point. Yes: 2009-05-31 Bruno Haible <[email protected]> * lib/alignof.h (alignof_slot, alignof_type, alignof): Document restriction due to compiler bugs. Reported by Eric Blake. --- lib/alignof.h.orig 2009-05-31 21:44:52.000000000 +0200 +++ lib/alignof.h 2009-05-31 21:44:22.000000000 +0200 @@ -21,7 +21,9 @@ #include <stddef.h> /* Determine the alignment of a structure slot (field) of a given type, - at compile time. Note that the result depends on the ABI. */ + at compile time. Note that the result depends on the ABI. + Note: The result cannot be used as a value for an 'enum' constant, + due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ #if defined __cplusplus template <class type> struct alignof_helper { char __slot1; type __slot2; }; # define alignof_slot(type) offsetof (alignof_helper<type>, __slot2) @@ -33,7 +35,9 @@ Note that this is not necessarily the same as alignof_slot(type). For example, with GNU C on x86 platforms: alignof_type(double) = 8, but - when -malign-double is not specified: alignof_slot(double) = 4, - - when -malign-double is specified: alignof_slot(double) = 8. */ + - when -malign-double is specified: alignof_slot(double) = 8. + Note: The result cannot be used as a value for an 'enum' constant, + due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ #if defined __GNUC__ # define alignof_type __alignof__ #else @@ -42,7 +46,8 @@ /* alignof is an alias for alignof_slot semantics, since that's what most callers need. - Note: The result cannot be used as a value for an 'enum' constant, */ + Note: The result cannot be used as a value for an 'enum' constant, + due to bugs in HP-UX 10.20 cc and AIX 3.2.5 xlc. */ #define alignof alignof_slot #endif /* _ALIGNOF_H */
