Converting To And From GMT / UTC Time In ColdFusion Using DateConvert()

Posted May 27, 2009 at 9:18 AM

Tags: ColdFusion

A few days ago, I started looking into using GMT (Greenwich Mean Time) and UTC (Universal Time Coordinated) times in ColdFusion. Specifically, I was looking into creating HTTP headers that required time to be sent in a special GMT-based HTTP time format. As I posted yesterday, I could easily get HTTP time stamps using GetHTTPTimeString(); this ColdFusion method would automatically convert from local time to GMT time and then format the date/time value for use with HTTP headers. I also demonstrated that you could use DateAdd() to convert to and from UTC time as well.

In the comments to my post yesterday, John Piotrowski pointed out that my DateAdd() calculations could be even more easily done with ColdFusion's DateConvert() method. From the documentation, DateConvert() takes a conversion type (Local2UTC / UTC2Local) and a date/time stamp. To make sure that this was an equivalent short-hand to DateAdd(), I ran a few quick tests:

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  • <!--- Get the current time. --->
  • <cfset dtNow = Now() />
  •  
  • <!---
  • Convert the date to GMT using DateAdd() and DateConvert()
  • to make sure that they are the same.
  • --->
  • DateAdd(): #DateAdd( "s", GetTimeZoneInfo().UTCTotalOffset, dtNow )#
  • <br />
  •  
  • DateConvert(): #DateConvert( "Local2UTC", dtNow )#
  • <br />

I this test, I am comparing DateAdd() and DateConvert() when converting the local time to UTC time. When I run the above code, I get the following output:

DateAdd(): {ts '2009-05-27 13:13:59'}
DateConvert(): {ts '2009-05-27 13:13:59'}

Exactly the same. Now, this is probably not needed at all, but I ran a test in the opposite direction as well just to make sure all was right with the world:

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  • <!--- Get the GMT time. --->
  • <cfset dtGMT = ParseDateTime(
  • GetHTTPTimeString( Now() )
  • ) />
  •  
  • <!--- Convert from GTM back to local time. --->
  • Now: #Now()#
  • <br />
  •  
  • DateConvert(): #DateConvert( "UTC2Local", dtGMT )#
  • <br />

When I run the above code I get the following output:

Now: {ts '2009-05-27 09:13:59'}
DateConvert(): {ts '2009-05-27 09:13:59'}

As you can see from the above demonstrations, DateConvert() is an effective shorthand for the combination of DateAdd() and GetTimeZoneInfo(). Thanks John Piotrowski, you rock!

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