Jarkko Hietaniemi > perl > Time::Local

Download:
perl-5.8.1.tar.gz

Dependencies

Annotate this POD

Related Modules

Date::Calc
Date::Manip
Crypt::SSLeay
Data::Dumper
File::Find
Time::localtime
Date::Parse
CGI::Carp
IO::Socket
Time::ParseDate
more...
By perlmonks.org
Module Version: 1.07   Source   Latest Release: perl-5.6.2

NAME ^

Time::Local - efficiently compute time from local and GMT time

SYNOPSIS ^

    $time = timelocal($sec,$min,$hour,$mday,$mon,$year);
    $time = timegm($sec,$min,$hour,$mday,$mon,$year);

DESCRIPTION ^

These routines are the inverse of built-in perl functions localtime() and gmtime(). They accept a date as a six-element array, and return the corresponding time(2) value in seconds since the system epoch (Midnight, January 1, 1970 UTC on Unix, for example). This value can be positive or negative, though POSIX only requires support for positive values, so dates before the system's epoch may not work on all operating systems.

It is worth drawing particular attention to the expected ranges for the values provided. The value for the day of the month is the actual day (ie 1..31), while the month is the number of months since January (0..11). This is consistent with the values returned from localtime() and gmtime().

The timelocal() and timegm() functions perform range checking on the input $sec, $min, $hour, $mday, and $mon values by default. If you'd rather they didn't, you can explicitly import the timelocal_nocheck() and timegm_nocheck() functions.

        use Time::Local 'timelocal_nocheck';

        {
            # The 365th day of 1999
            print scalar localtime timelocal_nocheck 0,0,0,365,0,99;

            # The twenty thousandth day since 1970
            print scalar localtime timelocal_nocheck 0,0,0,20000,0,70;

            # And even the 10,000,000th second since 1999!
            print scalar localtime timelocal_nocheck 10000000,0,0,1,0,99;
        }

Your mileage may vary when trying these with minutes and hours, and it doesn't work at all for months.

Strictly speaking, the year should also be specified in a form consistent with localtime(), i.e. the offset from 1900. In order to make the interpretation of the year easier for humans, however, who are more accustomed to seeing years as two-digit or four-digit values, the following conventions are followed:

The scheme above allows interpretation of a wide range of dates, particularly if 4-digit years are used.

Please note, however, that the range of dates that can be actually be handled depends on the size of an integer (time_t) on a given platform. Currently, this is 32 bits for most systems, yielding an approximate range from Dec 1901 to Jan 2038.

Both timelocal() and timegm() croak if given dates outside the supported range.

IMPLEMENTATION ^

These routines are quite efficient and yet are always guaranteed to agree with localtime() and gmtime(). We manage this by caching the start times of any months we've seen before. If we know the start time of the month, we can always calculate any time within the month. The start times are calculated using a mathematical formula. Unlike other algorithms that do multiple calls to gmtime().

timelocal() is implemented using the same cache. We just assume that we're translating a GMT time, and then fudge it when we're done for the timezone and daylight savings arguments. Note that the timezone is evaluated for each date because countries occasionally change their official timezones. Assuming that localtime() corrects for these changes, this routine will also be correct.

BUGS ^

The whole scheme for interpreting two-digit years can be considered a bug.

The proclivity to croak() is probably a bug.

SUPPORT ^

Support for this module is provided via the perl5-porters@perl.org email list. See http://lists.perl.org/ for more details.

Please submit bugs using the RT system at bugs.perl.org, the perlbug script, or as a last resort, to the perl5-porters@perl.org list.

AUTHOR ^

This module is based on a Perl 4 library, timelocal.pl, that was included with Perl 4.036, and was most likely written by Tom Christiansen.

The current version was written by Graham Barr.

It is now being maintained separately from the Perl core by Dave Rolsky, <autarch@urth.org>.

syntax highlighting: