User Guide

Table Of Contents

178 Chapter 9: Writing and Calling User-Defined Functions

Calling user-defined functions

You can call a function anywhere that you can use an expression, including in number signs (#) in

cfoutput tag, in a CFScript, or in a tag attribute value. One function can call another function,

and you can use a function as an argument to another function.

You can call a UDF in two ways:

• With unnamed, positional arguments, as you would call a built-in function

• With named arguments, as you would use attributes in a tag

You can use either technique for any function. However, if you use named arguments, you must

use the same argument names to call the function as you use to define the function. You cannot

call a function with a mixture of named and unnamed arguments.

One example of a user-defined function is a TotalInterest function that calculates loan payments

based on a principal amount, annual percentage, and loan duration in months. (For this

function’s definition, see “A user-defined function example” on page 192). You might call the

function without argument names on a form’s action page, as follows:

Interest: #TotalInterest(Form.Principal, Form.Percent, Form.Months)#

</cfoutput>

You might call the function with argument names, as follows:

Interest: #TotalInterest(principal=Form.Principal, annualPercent=Form.Percent,

months=Form.Months)#

</cfoutput>

Working with arguments and variables in functions

Good argument naming practice

An argument’s name should represent its use. For example, the following code is unlikely to result

in confusion:

function SumN(Addend1,Addend2)

{ return Addend1 + Addend2; }

</cfscript>

The following, similar code is more likely to result in programming errors:

function SumN(x,y)

{ return x + y; }

</cfscript>