User Guide

Table Of Contents

Creating user-defined functions 177

Using a CFML tag in a user-defined function

The most important advantage of using the

cffunction tag over defining a function in CFScript

is that you can include CFML tags in the function. Thus, UDFs can encapsulate activities, such

as database lookups, that require ColdFusion tags. Also, you can use the

cfoutput tag to display

output on the calling page with minimal coding.

Tip: To improve performance, avoid using the cfparam tag in ColdFusion functions. Instead, use the

cfset tag.

The following example function looks up and returns an employee’s department ID. It takes one

argument, the employee ID, and looks up the corresponding department ID in the

cfdocexamples Employee table:

SELECT Dept_ID

FROM Employee

WHERE Emp_ID = #empID#

</cfquery>

</cffunction>

Rules for function definitions

The following rules apply to functions that you define using CFScript or the

cffunction tag:

• The function name must be unique. It must be different from any existing variable, UDF, or

built-in function name, except you can use the ColdFusion advanced security function names.

• The function name must not start with the letters cf in any form. (For example,

CF_MyFunction, cfmyFunction, and cfxMyFunction are not valid UDF names.)

• You cannot redefine or overload a function. If a function definition is active, ColdFusion

generates an error if you define a second function with the same name.

• You cannot nest function definitions; that is, you cannot define one function inside another

function definition.

• The function can be recursive, that is, the function definition body can call the function.

• The function does not have to return a value.

You can use tags or CFScript to create a UDF. Each technique has advantages and disadvantages.