I need to convert time from GMT to Chicago local time.

Well, right now in CDST (Central Daylight Standard Time), Add 5 hours to local time to get the time in Greenwich England. When Chicago "goes off daylight savings time", (like the saying: "fall back"), the time difference will be 6 hours instead of 5 hours.

There are various Perl modules that calculate date/times. But basically they all involve a "trip through GMT". GMT in a Unix sense, is a continuously incrementing number of seconds. CST or CDST is a presentation of GMT. 1:30 AM local time could possibly mean 2 different GMT times for the same local day/time ( the "spring forward, fall back" idea). What "local time" is, is a political decision.

There is a boundary condition. But essentially the date/time module will know whether to subtract 5hrs*60min*60sec or 6hrs*60min*60sec from Unix "GMT epoch seconds" to get local time. Hard code this or ask a module that has a continuously updated database.

In reply to Re: GMT to Chicago TIme by Marshall
in thread GMT to Chicago TIme by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.