User Guide

670 Chapter 3: ColdFusion Functions

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.

The return value is 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.

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

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.

The value of "form.myString" is

<cfoutput>#form.myString#</cfoutput>

Parameter Description

variable_name String, enclosed in quotation marks. Name of variable to test for.