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up vote 4 down vote favorite
3

Here's the sort of time formatting I'm after:

2009-10-08 04:31:33.918700000 -0500

I'm currently using this:

strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S %Z", ts);

Which gives:

2009-10-11 13:42:57 CDT

Which is close, but not exact. I can't seem to find anything on displaying -0500 at the end. Plus I'm getting the seconds as an int.

How can I resolve these two issues?

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3 Answers

up vote 8 down vote accepted

I came up with this:

    char            fmt[64], buf[64];
    struct timeval  tv;
    struct tm       *tm;

    gettimeofday(&tv, NULL);
    if((tm = localtime(&tv.tv_sec)) != NULL)
    {
            strftime(fmt, sizeof fmt, "%Y-%m-%d %H:%M:%S.%%06u %z", tm);
            snprintf(buf, sizeof buf, fmt, tv.tv_usec);
            printf("'%s'\n", buf); 
    }

Fixes for the problems you had:

  • Use gettimeofday(), and struct timeval, which has a microseconds member for the higher precision.
  • Use a two-step approach, where we first build a string containing all the data except the microseconds.
  • Use lower-case 'z' for the timezone offset. This seems to be a GNU extension.

I tried re-creating the timezone offset manually, through the second struct timezone * argument of gettimeofday(), but on my machine it returns an offset of 0 which is not correct. The manual page for gettimefday() has quite a lot to say about the handling of timezones under Linux (which is the OS I tested on).

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%z is still non-standard =) –  gnud Oct 11 '09 at 20:18
    
Thanks, this is the closest I've gotten so far. The '%%06u' is just throwing garbage data back at me right now but the rest works well. P.S Yes, I know the %z is non-standard, but I'll take it :) –  Vlad the Impala Oct 11 '09 at 20:40
    
@aditya: That's weird ... The code above should work. Make sure you provide the second snprintf() call with a proper unsigned microseconds value to use for the %06u format. You can try printing the result after the strftime() call, you should see your final output except for the %06u sequence after the period. –  unwind Oct 11 '09 at 20:55
2  
It seems everyone here have missed the fact that %z is completely standard C99. It's in (the freely available) draft n1256 (tc3 working paper) as well as the official standard document, and it is also specified in POSIX (pubs.opengroup.org/onlinepubs/9699919799/functions/…). –  Quantumboredom Mar 21 '13 at 19:11
    
tv.tv_usec is type suseconds_t. Have not found a % modifier for it. Maybe a cast to (unsigned long) and use %06lu. (or cast to (uintmax_t) and use PRIuMAX. –  chux Aug 25 '13 at 0:47
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up vote 1 down vote

"%Y-%m-%d %T %z", but it seems %z is a GNU extension.

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%T does not give the sub-second digits asked for in the question. –  unwind Oct 11 '09 at 20:22
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up vote 1 down vote

%z (lower case z).

However, this does not appear in the Posix specification. Google took me in a circle back here.

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