ColdFusion Variables
Variables are a standard part of any programming language. A variable can be visualised as a container that stores a value.
We can use variables in many circumstances. For example, we could store the user's name inside a variable. We could then present the user's on the web page they're visiting. We could also perform a test against the variable to see what the value is. The application could then perform a different action depending on the value of the variable.
Using cfset
Syntax
To set a ColdFusion variable, use the cfset tag. To output the variable, you need to surround the variable name with hash (#) symbols and enclose it within cfoutput tags.
<cfset variablename="value">
<cfoutput>
#variablename#
</cfoutput>
Example of Usage
This example uses the cfset tag to declare a variable called "firstname" and assign a value of "bono" to it. It then outputs the contents of the variable.
ColdFusion code:
<cfset firstname="Bono">
<cfoutput>
Hello #firstname#.
</cfoutput>
Display in browser:
Hello Bono.
Using cfparam
The cfparam tag creates a variable if it doesn't already exist. You can assign a default value using the default attribute. This can be handy if you want to create a variable, but don't want to overwrite it if it has already been created elsewhere.
Example 1
In this example, the variable hasn't been set previously, so it will be assigned with the cfparam tag.
<cfparam name="firstName" default="Ozzy">
<cfoutput>
Hello #firstName#
</cfoutput>
This results in the following:
Hello Ozzy
Example 2
In this example, the variable has already been assigned (using the cfset tag), so this value will override the default value in the cfparam tag.
<cfset firstname="Barney">
<cfparam name="firstName" default="Ozzy">
<cfoutput>
Hello #firstName#
</cfoutput>
This results in the following:
Hello Barney
Checking if a Variable Exists
You can check if a variable has been defined or not by using ColdFusion's built in IsDefined() function. This can be used inside a cfif tag to prevent nasty error messages in the event you attempt to refer to a variable that doesn't exists. You could also use this function to determine whether a user has performed a certain action or not.
<cfif IsDefined("firstName")>
Hello #firstname#!
<cfelse>
Hello stranger!
</cfif>