Re: [tlug] It's time_t to Party!

[Jim <jep200404@example.com>]

Michal Hajek wrote:

> printf("... %d.%09ld\n",> (int)ts.tv_sec, (long int)ts.tv_nsec);

I'm focusing on the type of the .tv_sec element. 
On a box I use, it is a type_t type. 

Unfortunately, I don't know how to say: 

   printf("%(type_t)d...",ts.tv_sec); 

which would be automatically be correct when type_t changes, 
or even better: 

   printf("%(typeof ts.tv_sec)d...",ts.tv_sec);

which would spare one from having to scrutinize the man pages 
(although one would still have to know that .tv_sec is an 
integral type), so one is stuck commiting to making a choice to 
use l or to not use l between % and d in the format string. 
On a box I use: 

   .tv_sec is a type_t, which is a __type_t, which is a __TIME_T_TYPE, 
   which is a __SLONGWORD_TYPE, which is a long int. 

Yuch! It was too hard to follow that chain of definitions 
with repeated grep -i foo /usr/include commands. There is 
such a hall of mirrors effect that one is not confident what 
the heck tv_sec is. 

I would figure the safer choice, would be to cast to a long 
(and use %ld) instead of a mere int. At worst, the cast to 
long slows down printf. At worst, the cast to int chops off 
significant bits. Granted, with 32-bit ints, that won't happen 
for about another 30 years, 

   http://en.wikipedia.org/wiki/Unix_epoch#32-bit_overflow
   http://en.wikipedia.org/wiki/Year_2038_problem
   http://en.wikipedia.org/wiki/Unununium_Time#System_time

and even then computers would likely have migrated to 64-bit 
ints time_t's which would make the issue moot, but that's what 
folks were saying about four-digit numbers for years in the (19)60s. 
(And what format is the data stored in?) It's like deja-vu all 
over again with Y2K. Some organizations already have to deal with 
this kind of issue, and just use their own format, like 
YYYY-MM-DD HH:MM:SS.sssssssssss...

If it's for production code, I would first consider something 
that would avoid the need for any cast, then consider casting 
to a long. Casting to an int would be my last consideration. 
Of course, if your code is just a short term testing hack, 
then it doesn't matter. 

Of course, a completely different consideration would be to 
avoid using printf(), or the loosely typed C language. 
Some things are just best done in Emacs. 

   http://en.wikipedia.org/wiki/Unix_epoch#time_t_parties

Jim