You can create your own custom functions, known as user-defined functions, or UDFs. You then use them in your application pages the same way you use standard ColdFusion functions. You can also organize functions you create by grouping related functions into ColdFusion components. For more information, see Building and Using ColdFusion Components.

When you create a function for an algorithm or procedure that you use frequently, you can then use the function wherever you require the procedure. If you must change the procedure, you change only one piece of code. You can use your function anywhere that you can use a ColdFusion expression: in tag attributes, between number (#) signs in output, and in CFScript code. 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/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, including routines to determine the space available on a Windows file system drive

For information about selecting among user-defined functions, ColdFusion components, and custom tags, see Creating ColdFusion Elements.