Poul-Henning Kamp said:
>>> #define timespecsub(vvp, uvp) \
>>> do { \
>>> (vvp)->tv_sec -= (uvp)->tv_sec; \
>>> (vvp)->tv_nsec -= (uvp)->tv_nsec; \
>>> if ((vvp)->tv_nsec < 0) { \
>>> (vvp)->tv_sec--; \
>>> (vvp)->tv_nsec += 1000000000; \
>>> } \
>>> } while (0)
>>>
>>> Lovely, isn't it ?
>> Unlovely, but not the ugliest, especially considering that there may
>> not have been a better way at the time.
>> The 'do { ... } while (0)' kludge is at least as ugly as its contents[...]
> The do {...} while(0) is the least ugly way to make function-like CPP
> macros safe for below average programmers IMO.
For below-average programmers to write, perhaps. The obvious way for a
competent programmer to write this without that horrible hack is:
#define timespecsub(vvp, uvp) \
((vvp)->tv_sec -= (uvp)->tv_sec, \
(vvp)->tv_nsec -= (uvp)->tv_nsec, \
((vvp)->tv_nsec < 0) \
? ((vvp)->tv_sec--, (vvp)->tv_nsec += 1000000000) \
: (void) 0)
This has the advantage of being usable wherever a function can appear.
Of course, since it evaluates its arguments multiple times, the usual
convention is to put the name in uppercase.
But with a modern compiler I'd just write it as a function (possibly an
inline one) and let the compiler worry about efficiency.
--
Clive D.W. Feather | If you lie to the compiler,
Email: [email protected] | it will get its revenge.
Web: http://www.davros.org | - Henry Spencer
Mobile: +44 7973 377646
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