User Guide

164 Chapter 8: Creating ColdFusion Elements
Recommended uses
Consider using the
cfinclude tag in the following cases:
• For page headers and footers
• To divide a large page into multiple logical chunks that are easier to understand and manage
• For large “snippets” of code that are used in many places but do not require parameters or fit
into the model of a function or tag
About user-defined functions
User-defined functions (UDFs) let you create application elements in a format in which you pass
in arguments and get a return a value. You can define UDFs using CFScript or the
cffunction
tag. The two techniques have several differences, of which the following are the most important:
• If you use the cffunction tag, your function can include CFML tags.
• If you write your function using CFScript, you cannot include CFML tags.
You can use UDFs in your application pages just as you use standard ColdFusion functions.
When you create a function for an algorithm or procedure that you use frequently, you can then
use the function wherever you need the procedure, just as you would use a ColdFusion built-in
function. For example, the following line calls the function MyFunct and passes it two arguments:
<cfset returnValue=MyFunct(Arg1, Arg2)>
You can group related functions in a ColdFusion component. For more information, see “Using
ColdFusion components” on page 165.
As with custom tags, you can easily distribute UDFs to others. For example, the Common
Function Library Project at www.cflib.org is an open-source collection of CFML user-defined
functions.
Recommended uses
Typical uses of UDFs include, but are not limited to, the following:
• Data manipulation routines, such as a function to reverse an array
• String and date and time routines, such as a function to determine whether a string is a valid IP
address
• Mathematical calculation routines, including standard trigonometric and statistical operations
or calculating loan amortization
• Routines that call functions externally, for example using COM or CORBA, such as routines
to determine the space available on a Windows file system drive
Consider using UDFs in the following circumstances:
• You must pass in a number of arguments, process the results, and return a value. UDFs can
return complex values, including structures that contain multiple simple values.
• You want to provide logical units, such as data manipulation functions.
• Your code must be recursive.
• You distribute your code to others.