User Guide

IsDefined 533
IsDefined
Description
Evaluates a string value to determine whether the variable named in it exists.
This function is an alternative to the
ParameterExists function, which is deprecated.
Returns
True, if the variable is found, or, for a structure, if the specified key is defined; False, otherwise.
Returns False for an array or structure element referenced using bracket notation. For example,
IsDefined("myArray[3]") always returns False, even if the array element myArray[3] has a
value.
Category
Decision functions
Function syntax
IsDefined("variable_name")
See also
Evaluate
History
ColdFusion MX: Changed behavior: this function can process only the following constructs:
• a simple variable
• a named variable with dot notation
• a named structure with dot notation (for example: mystruct.key)
Parameters
Usage
When working with scopes that ColdFusion exposes as structures, the StructKeyExists
function can sometimes replace this function. The following lines are equivalent:
if(isDefined("form.myVariable"))
if(structKeyExists(form,"myVariable"))
Example
<cfif IsDefined("form.myString")>
<p>The variable form.myString has been defined, so show its contents.
This construction allows us to place a form and its resulting action code
on the same page and use IsDefined to control the flow of execution.</p>
<p>The value of "form.myString" is <b><i>
<cfoutput>#form.myString#</cfoutput></i></b>
<cfelse>
<p>During the first time through this template, the variable "form.myString"
has not yet been defined, so we do not try to evaluate it.
</cfif>
<form action="#CGI.Script_Name" method="POST">
<input type="Text" name="MyString" value="My sample value">
Parameter Description
variable_name String, enclosed in quotation marks. Name of variable to test for.