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Re: time

From Nobody <nobody@nowhere.com>
Subject Re: time
Date 2012-11-20 03:07 +0000
Message-Id <pan.2012.11.20.03.07.29.506000@nowhere.com>
Newsgroups comp.lang.c
References <k8ehrs$ddf$1@dont-email.me>
Organization Zen Internet

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On Mon, 19 Nov 2012 19:11:41 -0500, Bill Cunningham wrote:

>     I am using the time and date in my code using asctime () time(), and
> localtime(). I know in POSIX they are obsolete but I am concerned with
> c89-99. strftime() is suppoed to be the function used now.

All of those are in C89 and C99. POSIX considers asctime() and ctime()
deprecated in favour of strftime(), as the former use a hard-coded format
with English day and month names.

The others aren't deprecated, although the POSIX-specific re-entrant
functions (gmtime_r, localtime_r) may be preferred over the standard ISO C
equivalents (gmtime, localtime) for various reasons.

> I get the time
> and date just fine with the code I've written but I want to use the time
> to seed a random number generator. I don't know if I want seconds from
> epoch or what. Any input?

The simple solution is srand(time(NULL)). However, time() only has a one
second resolution, so consecutive invocations of the program may produce
identical results. ISO C doesn't provide any mechanism to query the time
with greater resolution; POSIX defines gettimeofday() with microsecond
resolution and clock_gettime() with nanosecond resolution.

For testing, it's often useful to be able to reproduce prior results, so
it may be wise to allow a seed to be specified explicitly (e.g. via a
command-line argument or environment variable), with seeding from the
current time as a fall-back.

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Thread

time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-19 19:11 -0500
  Re: time Geoff <geoff@invalid.invalid> - 2012-11-19 16:26 -0800
    Re: time Keith Thompson <kst-u@mib.org> - 2012-11-19 16:51 -0800
      Re: time Geoff <geoff@invalid.invalid> - 2012-11-19 17:01 -0800
      Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-19 20:07 -0500
        Re: time Keith Thompson <kst-u@mib.org> - 2012-11-19 23:54 -0800
          Re: time pete <pfiland@mindspring.com> - 2012-11-20 07:31 -0500
          Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-20 17:09 -0500
  Re: time Keith Thompson <kst-u@mib.org> - 2012-11-19 16:30 -0800
    Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-19 20:04 -0500
      Re: time Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:52 -0800
  Re: time Nobody <nobody@nowhere.com> - 2012-11-20 03:07 +0000
    Re: time Keith Thompson <kst-u@mib.org> - 2012-11-19 23:58 -0800
    Re: time Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2012-11-21 08:30 -0800
      Re: time "osmium" <r124c4u102@comcast.net> - 2012-11-21 11:11 -0600
      Re: time James Kuyper <jameskuyper@verizon.net> - 2012-11-21 12:22 -0500
        Re: time gof@somewhere.invalid (Adam Wysocki) - 2012-11-21 19:09 +0000
          Re: time Keith Thompson <kst-u@mib.org> - 2012-11-21 12:01 -0800
            Re: time gof@somewhere.invalid (Adam Wysocki) - 2012-11-23 08:15 +0000
          Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-21 15:16 -0500
            Re: time "osmium" <r124c4u102@comcast.net> - 2012-11-21 14:23 -0600
              Re: time Rosario1903 <Rosario@invalid.invalid> - 2012-11-22 10:25 +0100
            Re: time Keith Thompson <kst-u@mib.org> - 2012-11-21 12:30 -0800
              Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-21 18:24 -0500
            Re: time Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:56 -0800
          Re: time Nobody <nobody@nowhere.com> - 2012-11-22 02:00 +0000
            Re: time Keith Thompson <kst-u@mib.org> - 2012-11-21 19:57 -0800
              Re: time gof@somewhere.invalid (Adam Wysocki) - 2012-11-23 08:31 +0000
            Re: time army1987 <army1987@ask-for-it.invalid> - 2012-11-24 13:58 +0000
          Re: time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-22 11:36 +0000
            Re: time gof@somewhere.invalid (Adam Wysocki) - 2012-11-23 08:20 +0000
              Re: time Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-23 14:31 +0000
      Re: time Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:54 -0800
  Re: time Mark Storkamp <mstorkamp@yahoo.com> - 2012-11-20 08:34 -0600
    Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-20 20:37 -0500
      Re: time Keith Thompson <kst-u@mib.org> - 2012-11-20 20:25 -0800
        Re: time "Bill Cunningham" <nospam@nspam.invalid> - 2012-11-21 15:11 -0500

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