What is up with this in ColdFusion's DecimalFormat() function? How do I get the correct result?

Question

<cfset number1 = 20.5/80 * 100 />
<cfset number2 = 18.125 />
<cfset number3 = 6.875 />

<cfoutput>
DecimalFormat(#number1#): #DecimalFormat(number1)#<br />
DecimalFormat(#number2#): #DecimalFormat(number2)#<br />
DecimalFormat(#number3#): #DecimalFormat(number3)#
</cfoutput>

OUTPUTS:

DecimalFormat(25.625): 25.62

DecimalFormat(18.125): 18.13

DecimalFormat(6.875): 6.88

RATHER THAN OUTPUTING:

DecimalFormat(25.625): 25.63

DecimalFormat(18.125): 18.13

DecimalFormat(6.875): 6.88

It seems that a variable that is the result of a mathematical calculation makes DecimalFormat() behave differently. Any quick fix, without digging into java?

Answer 1

I think the problem is not DecimalFormat(), but the typical floating-point rounding errors.

see: PrecisionEvaluate()

Answer 2

DecimalFormat is a formatting function. Not a Mathematical function. Its job is not to round your number for you, unfortunately CF lacks good mathematical functions for decimals so you will have to write your own.

Here is one someone wrote on the CF livedocs page for round():

 <cffunction name="roundDecimal" returntype="numeric"> 
     <cfargument name="num" type="numeric" required="yes"> 
     <cfargument name="decimal" type="numeric" default="2" required="no"> 

     <cfreturn round(num*10^decimal)/10^decimal /> 
  </cffunction>

Answer 3

A quick fix would be to change line 1 to number1 = NumberFormat(20.5/80 * 100,'9.999')

Answer 4

Please see the CF documentation NumberFormat and do a page search on round to see some specific information.