| From: | "Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx> |
| Date: | Thu, 6 Jan 2005 10:34:23 +0100 |
On Thursday, 6. January 2005 10:00, Adrian Bocaniciu wrote:
> As I have already mentioned in a follow-up to my recent bug report, the
> essential ports net/quagga and net/zebra have been totally broken by the
> use of lower-case macros in the DragonFly system headers.
>
> There is an old C tradition that the identifiers used in macro
> definitions must be written entirely with capital letters and that no
> other identifiers should be written like that. This tradition has not
> been caused by esthetic reasons but by the need to separate the name
> spaces for macros and for other identifiers.
I think you are mistaking something here. Macros are traditionally written
upper case if they evaluate their arguments more than one time, iirc.
If you want to be portable, #define POSIX_SOURCE or what it is called and
don't include sys/* files. These lower case macros are usually for
convenience or compatibility.
For example <netdb.h>:
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses from name server */
#define h_addr h_addr_list[0] /* address, for backward compatibility */
};
as you can see, it's an often used compatibility define. and those are usually
prefixed with an acronym from the struct (h_). Unfortunately, conflicts
happen, but you can't avoid it. Removing those defines would result in a much
larger breakage, I'd guess.
> In the case of net/route.h, where I first encountered such macros, they
> were used to provide alternate names for some structure members. That
> can be done in a perfectly safe way without macros, by using anonymous
> unions. Even if, for some very stupid reason (as the named unions were
> really a mistake in the original C design) the anonymous unions have not
> made their way yet into the official C standard, gcc and most other C
> compilers support anonymous unions also in C, not only in C++.
I'm not sure if this will always work. Could you give an example which will
compile with gcc2 and gcc34 without warnings?
cheers
simon
--
/"\
\ /
\ ASCII Ribbon Campaign
/ \ Against HTML Mail and News
Attachment:
pgp00001.pgp
Description: PGP signature