Am 09.12.2013 21:08, schrieb Jonathan Nieder: > Karsten Blees wrote: > >> GCC supports __packed__ as of 2.3 (1992), so any other compilers >> that copied the __attribute__ feature probably won't complain. > > Alas, it looks like HP C doesn't support __packed__ (not that I > care much about HP C): > > http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/Online_Help/pragmas.htm#Attributes > Thanks for the link > Maybe a macro expanding to __attribute__((aligned(1))) on the fields > would work? The same macro could expand to __declspec(align(1)) in > the MSVC build. > But alignment is not the same as packing. We still want the structure to be 8-byte aligned (i.e. variables of the type should start at 8-byte boundaries). We just don't want the size of the structure to be padded to a multiple of 8, so that we can extend it without penalty. (Besides, __attribute__((aligned)) / __declspec(align) can only _increase_ the alignment, so aligned(1) would have no effect). Googling some more, I believe the most protable way to achieve this via 'compiler settings' is #pragma pack(push) #pragma pack(4) struct hashmap_entry { struct hashmap_entry *next; unsigned int hash; }; #pragma pack(pop) This is supported by at least GCC, MSVC and HP (see your link). The downside is that we cannot use macros (in git-compat-util.h) to emit #pragmas. But we wouldn't have to, as compilers aren't supposed to barf on unknown #pragmas. However, considering the portability issues, the macro solution (injecting just the two fields instead of a struct) becomes more and more attractive in my mind... Karsten -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html