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Re: time

From Nobody <nobody@nowhere.com>
Subject Re: time
Date 2012-11-22 02:00 +0000
Message-Id <pan.2012.11.22.02.00.18.990000@nowhere.com>
Newsgroups comp.lang.c
References <k8ehrs$ddf$1@dont-email.me> <pan.2012.11.20.03.07.29.506000@nowhere.com> <8dd71a20-5caa-4e4a-8c1f-5c7d84b56bd2@h9g2000yqd.googlegroups.com> <50AD0DC6.5090505@verizon.net> <gof.1353524440.12609@somewhere.invalid>
Organization Zen Internet

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On Wed, 21 Nov 2012 19:09:18 +0000, Adam Wysocki wrote:

>> If srand(time(NULL)) were used in that program, it would generate the
>> same exact sequence of random numbers for all requests received during
>> the same second.
> 
> Maybe adding process ID to the seed calculation would do the job.

It would, and that's common. But there's no portable way to read the PID
(if such a concept even exists on a given platform).

The main issue is that time() appears to be about the only portable source
of non-determinism available, and it's typically rather weak.

On Wed, 21 Nov 2012 12:01:46 -0800, Keith Thompson wrote:

> If it's worth going to that much trouble, it's probably worth using a
> better random number generator than rand() (one provided by the
> implementation but not specified by the C standard).

But that doesn't do anything about the lack of non-determinism (entropy).
A better PRNG may give you better random numbers, but without something
other than time(), they'll be exactly the same random numbers as any
other invocation which gets the same value from time().

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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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