Path: utzoo!attcan!uunet!snorkelwacker!apple!oliveb!orc!mipos3!iwarp.intel.com!news
From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: A head start (was Re: reverse of localtime())
Message-ID: <1990Feb28.160935.28518@iwarp.intel.com>
Date: 28 Feb 90 16:09:35 GMT
References: <1176@frankland-river.aaii.oz.au>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 53
In-Reply-To: pem@frankland-river.aaii.oz.au (Paul E. Maisano)

In article <1176@frankland-river.aaii.oz.au>, pem@frankland-river (Paul E. Maisano) writes:
| I am writing a perl program at the moment which is doing a lot of
| manipulation of dates and times.
| 
| I am maintaining a text file which contains dates such as 24/04/89 and
| to manipulate these dates easily I would like to convert that to "the
| number of seconds since Jan 1970". This is the reverse of what localtime()
| does. [I can't keep the number of seconds in the file rather than the
| date either since the file may be modified by hand.]

Well, as a headstart, here's what I did for 'newslat', which had to
convert a Usenet-standard date into an integer:

%offset = (
	'Jan89', 0, 'Feb89', 31, 'Mar89', 59,
	'Apr89', 90, 'May89', 120, 'Jun89', 151,
	'Jul89', 181, 'Aug89', 212, 'Sep89', 243,
	'Oct89', 273, 'Nov89', 304, 'Dec89', 334,
	'Jan90', 365, 'Feb90', 396, 'Mar90', 425,
	'Apr90', 456, 'May90', 486, 'Jun90', 516
); # that'll do for a while

### lotsa code deleted here ###
### we're in a loop named ARTICLE, $article is a filename, and $_ is the
### string: "Date: 24 June 90 11:23:45 GMT" for example

	unless (/\s(\d\d?)\s+(\w\w\w)\w*\s+(\d\d)\s+(\d\d?):(\d\d):(\d\d)\s+GMT/) {
		/(.*)/;
		warn "$article: unknown date format: $1";
		next ARTICLE;
	}
	($day,$monthname,$year,$hour,$minute,$second) = ($1,$2,$3,$4,$5,$6);
	unless (defined($offset{$monthname . $year})) {
		warn "$article: unknown month/year: $monthname/$year";
		next ARTICLE;
	}
	$when = ($offset{$monthname . $year}+$day-1)*86400 + $hour*3600 +
		$minute * 60 + $second + 599616000;

At this point, $when has the UNIX "seconds past Jan 1 1970 midnite
GMT" integer in it.  This routine is reasonably fast... the key is to
precompute the month/year offsets (I did it by hand :-) so that Perl
has only to perform a simple table lookup.

If you get a generic routine working, please forward it to me (or the
net).  I can also help you by email, if you need further assistance.

$\="hacker,";$,="another ";print"Just ","Perl ";
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Welcome to Portland, Oregon, home of the California Raisins!"=/