Everything You Must Know About ColdFusion Variables - Variable definition with CFSET tag
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In the earlier article the <cfset> tag was introduced. This tag sets the value of a variable. Trying to use a variable before it is assigned a value results in an error. The best practice is to test its existence before using it. Here is an example. This file undefined.cfm would produce an error, since the variable jac is not defined as shown in the picture below the code. As indicated in the error message, a more robust error message can be generated after changing the settings in the ColdFusion Administrator. We postpone this for later.
Syntax<CFSET variable_name=expression>
<cfoutput>#jac#</cfoutput>
Variable assignment with <cfparam> tag
The above problem could have been identified before calling the variable, by using some kind of logic. However, there is yet another way of avoiding the issue. This is by using the <cfparam> tag to define the variable. In fact, <cfparam> can not only be used in the context of a variable, but can also be used in a much wider range of variables, including simple data types as well as complex data types. Here is an example of its usage.
Syntax<CFPARAM NAME="param_name"
TYPE="data_type"
DEFAULT="value">
<!---Variable definition using CFPARAM tag--->
<!---Usage of <cfparam>--->
<!---If named parameter does not exist,
it returns the default specified--->
<cfparam name="jac" default="Okidoki">
<cfoutput>
Variable 'jac' is not defined<br/>
</cfoutput>
<!---<cfset jac="Jay">--->
<cfoutput>
My name is #jac#.
</cfoutput>
<hr>
<cfparam name="jac" default="Okidoki">
<cfoutput>
Variable 'jac' is defined as 'Jay'<br/>
</cfoutput>
<cfset jac="Jay">
<cfoutput>
My name is #jac#.
</cfoutput>
Now you look at the browser output when this file cfparam.cfm is browsed. In the first part, a variable was not defined and therefore the display was a default value. In the second part, a variable did exist and was defined. In this case the value of the variable was displayed.
Next: Variable by assigning statements in CFSCRIPT >>
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