time zone handling

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time zone handling

Page last updated 14 Dec 2011, by Hendrik Lipka. 11 replies time

When using NTP to set the current time, it is always set to UTC. The mbed libraries have no notion of timezone handling. This library can read time zone definitions, and can calculate the proper local time. It also handles the daylight savings.

Library

/users/hlipka/libraries/TimeZone

first, set up the time zone file as described below
make sure you have mounted the time zone file under /local
in your code, set the current time (preferably via an NTP call)
create a /Time/ object
whenever you need the current local time, create a TimeStamp object via the Time object
use the provided methods to get the time

A demo program can be found here (Note: is uses an NTP server suited for Germany, so you might want to change this).

Timezone files

This library uses time zones files in CSV format, as provided by this project.

go to the project page
download the most current data file (right now this is tzdata_2010o.zip)
extract it
go to the tzdata/csv folder
look for the csv file matching your location the best (use one of the global time zones, or by city divided by continents)
copy this file as 'timezone.csv' to the mbed USB disk

After that, use the library as described.

11 comments on time zone handling:

Aaron Goselin

# 02 Apr 2011

Thanks! This saves me some time.

George Novacek

# 01 May 2011

I've had a clock working OK until several days ago when suddenly the UTC time has been Jan 3, 1970. I've tried several sites such as "0.de.pool.ntp.org", and North American, Japanese, etc. All give the same result. Is it the server, and if it is, are there some others I could use?

Then, out of desparation, I tried this project with no changes. The UTC time problem remained while the screen prints "set time OK" and the .csv file does not load printing "error while reading timezone file". I used several, i.e. New York, Toronto,etc. with the same result. I use a HyperTerminal to print.

Any help? Regards George

Remco de Haar

# 30 Nov 2011

The link tzdata_2010o.zip is dead. Somebody have for me an alternative location? I try to find something similar on the internet but nothing there.

Thanks in advance!

Hendrik Lipka

# 30 Nov 2011

Hmm, this project seems to be dead. Maybe as reaction of this stupid timezone lawsuit. Fortunately, there is a clone to be found here. There is no ZIP available, you need to browse around for the file you need.

Remco de Haar

# 01 Dec 2011

Just what I need!

Thanks for your quick reaction!

BTW a lawsuit about a timezone integration? How stupid is that.

Hendrik Lipka

# 01 Dec 2011

Remco de Haar wrote:

BTW a lawsuit about a timezone integration? How stupid is that.

http://www.theregister.co.uk/2011/10/07/unix_time_zone_database_destroyed/

Pierre Emmibed

# 14 Dec 2011

Hendrik Lipka wrote:

Hmm, this project seems to be dead. Maybe as reaction of this stupid timezone lawsuit. Fortunately, there is a clone to be found here. There is no ZIP available, you need to browse around for the file you need.

I imported a timezone.csv file like this (header removed):

-9999-01-01T00:00:00Z,1893-03-31T23:06:32Z,3208,LMT,false
1893-03-31T23:06:32Z,1916-04-30T22:00:00Z,3600,CET,false
1916-04-30T22:00:00Z,1916-09-30T23:00:00Z,7200,CEST,true
1916-09-30T23:00:00Z,1917-04-16T01:00:00Z,3600,CET,false
1917-04-16T01:00:00Z,1917-09-17T01:00:00Z,7200,CEST,true
1917-09-17T01:00:00Z,1918-04-15T01:00:00Z,3600,CET,false
1918-04-15T01:00:00Z,1918-09-16T01:00:00Z,7200,CEST,true

and got the following error:

error while reading timezone file [timezone.csv]
time=13/14 15:20:49

Hendrik Lipka

# 14 Dec 2011

This error happens when the file cannot be found. Did you set up a local file system as "/local"?

The code in question look like this:

    FILE *fp = fopen("/local/timezone.csv", "r");

    if (fp==NULL) {
        printf("error while reading timezone file [timezone.csv]\n");
        return;
    }

As an additional note: try to comment out all the lines you don't need (e.g. everything before 2010 and after 2015), because otherwise you easily run out of memory.

Andras Tamas Magyar

# 09 Dec 2013

the cvs file no longer exist. Can someone upload it to somewhere please??

Hendrik Lipka

# 09 Dec 2013

As already noted, a copy can be found here.