zic.8 in html

Dave Rolsky autarch at urth.org
Thu Oct 9 19:48:08 UTC 2003

On Thu, 9 Oct 2003, Oscar van Vlijmen wrote:

> Some non-Unix and even non-C developers would like to use the timezone data,
> but they cannot find nor read the documentation.

If anyone's interested, I've implemented a Perl module that provides a
Perl API to the timezone database.  It parses the source text files and
generates Perl modules, rather than simply overlaying the C API, for a
number of reasons.  The main reason was that I wanted this to work outside
the bounds of the epoch, so using native time_t values wouldn't work.

Anyway, the module is called DateTime::TimeZone, and is at
http://search.cpan.org/dist/DateTime-TimeZone/.  It's part of a larger
project to provide decent date/time support for Perl.  More info on the
project can be found at datetime.perl.org.

BTW, writing a parser for the TZ data was a bit of a nightmare, as the
interrelations between observance changes and rules make it very complex
to figure out what rule is in effect at any given time.  I don't know if
there's a better way to represent this data, but explaining _how_ to do
this to someone who wants to write a parser is non-trivial.  The zic.8
file doesn't really explain the "how", just the "what".

Also, to make sure I was doing this correctly, I wrote some code to
generate tests based on zdump's output.  This is a script in the
DateTime::TimeZone distro called tools/tests_from_zdump.  People working
on providing a non-C API may find this script useful, as it generates
comprehensive tests for _every_ zone for _every_ change that zdump
outputs.  It could easily be adapted to generate tests for a different
language's API.


House Absolute Consulting

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