Convert Utc/Gmt Time to Local Time

Convert UTC datetime string to local datetime

If you don't want to provide your own tzinfo objects, check out the python-dateutil library. It provides tzinfo implementations on top of a zoneinfo (Olson) database such that you can refer to time zone rules by a somewhat canonical name.

from datetime import datetime
from dateutil import tz

# METHOD 1: Hardcode zones:
from_zone = tz.gettz('UTC')
to_zone = tz.gettz('America/New_York')

# METHOD 2: Auto-detect zones:
from_zone = tz.tzutc()
to_zone = tz.tzlocal()

# utc = datetime.utcnow()
utc = datetime.strptime('2011-01-21 02:37:21', '%Y-%m-%d %H:%M:%S')

# Tell the datetime object that it's in UTC time zone since 
# datetime objects are 'naive' by default
utc = utc.replace(tzinfo=from_zone)

# Convert time zone
central = utc.astimezone(to_zone)

Edit Expanded example to show strptime usage

Edit 2 Fixed API usage to show better entry point method

Edit 3 Included auto-detect methods for timezones (Yarin)

Java Convert GMT/UTC to Local time doesn't work as expected

I also recommend using Joda as mentioned before.

Solving your problem using standard Java Date objects only can be done as follows:

    // **** YOUR CODE **** BEGIN ****
    long ts = System.currentTimeMillis();
    Date localTime = new Date(ts);
    String format = "yyyy/MM/dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(format);

    // Convert Local Time to UTC (Works Fine)
    sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
    Date gmtTime = new Date(sdf.format(localTime));
    System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:"
            + gmtTime.toString() + "," + gmtTime.getTime());

    // **** YOUR CODE **** END ****

    // Convert UTC to Local Time
    Date fromGmt = new Date(gmtTime.getTime() + TimeZone.getDefault().getOffset(localTime.getTime()));
    System.out.println("UTC time:" + gmtTime.toString() + "," + gmtTime.getTime() + " --> Local:"
            + fromGmt.toString() + "-" + fromGmt.getTime());

Output:

Local:Tue Oct 15 12:19:40 CEST 2013,1381832380522 --> UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000
UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000 --> Local:Tue Oct 15 12:19:40 CEST 2013-1381832380000

Convert UTC date time to local date time

Append 'UTC' to the string before converting it to a date in javascript:

var date = new Date('6/29/2011 4:52:48 PM UTC');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"

How to convert from GMT/UTC to local time and back using momentjs?

Since your input represent UTC time, you have to use moment.utc (as suggested by others in the comments):

By default, moment parses and displays in local time.

If you want to parse or display a moment in UTC, you can use moment.utc() instead of moment().

Moreover, since your input string is not in a format recognized by moment(String) (ISO 8601 or RFC 2822), you have to pass format parameter as second argument of moment.utc, see String + Format parsing section of the docs.

Here a code sample:

var input = "December 25, 2018 01:02:20";
var fmt = 'MMMM DD, YYYY HH:mm:ss';
var m = moment.utc(input, fmt);
console.log(m.local().format(fmt));
console.log(m.utc().format(fmt));

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.21.0/moment.min.js"></script>

time_t t;
struct tm tm;
struct tm * tmp;
...
t = timegm(&tm);
...
tmp = gmtime(t);

t = mktime(&tm);
...
tmp = localtime(t);