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This is a cross post from something I just posted to the ColdFusion Cookbook, but since that site gets about a 100 hits a month or so, I figured I'd share it here as well.
Date comparisons are fairly easy in ColdFusion. One common task is to compare a date value to the current date and check if there is a match on the day, week, month, etc. For this entry we will consider comparing a date's century to the current century. This is a bit more complex. While ColdFusion has functions to retrieve parts of a date (seconds, minutes, day, month, etc) it does not have a function to return the century value. You can get this using a bit of math though.
Consider the following date:
<cfset d1 = createDate(2009, 1, 1)>
To get the century, you can first get the year, and then divide the value by 100, using the \ operator to round the result.
<cfoutput> #year(d1) \ 100# </cfoutput>
This results in 20 (technically we would call 2009 the 21st century, but we just need a unique value). You could then simply compare this value to the value you get using year(now()) to see if d1 is in the same century.