User Guide

266 Chapter 2: ColdFusion Tags

• To test whether an optional variable exists, use this tag with the name and default attributes.

If the variable does not exist, it is created and set to the

default attribute value. If the variable

exists, processing continues; the value is not changed.

If you specify

variableName for the returnType attribute, the parameter value must be a string

that is in ColdFusion variable name format; that is, starts with a letter, underscore (_), or Unicode

currency symbol, and contains letters, numbers, underscores, periods, and Unicode currency

symbols, only. ColdFusion does not check whether the parameter value corresponds to an existing

ColdFusion variable.

Tip: To improve performance, avoid using the cfparam tag in ColdFusion functions, including in CFC

methods. Instead, place the cfparam tags in the body of the CFML pages.

Example

<!--- This example shows how to use CFPARAM to define default values for page

variables -------->

</cfif>

<body>

<h3>cfparam Example</h3>

<p>cfparam is used to set default values so thata developer does not have to

check for the existence of a variable using a function like IsDefined.

<p>The default value of our tempVar is

"<cfoutput>#StoreTempVar# </cfoutput>"

<!--- check if tempVar is still the same as StoreTempVar

and that tempVar is not blank --->

<cfif tempVar is not #StoreTempVar#

and tempVar is not "">

<h3>The value of tempVar has changed: the new value is

<cfoutput>#tempVar#</cfoutput></h3>

</cfif>

<p>

Type in a new value for tempVar, and hit submit:<br>

</form>