IsDefined |
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Description
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Evaluates a string value to determine whether the variable named in it exists.
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This function is an alternative to the ParameterExists function, which is deprecated.
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Returns
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True, if the variable is found, or, for a structure, if the specified key is defined; False, otherwise.
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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.
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Category
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Decision functions
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Function syntax |
IsDefined("variable")
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See also
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Evaluate
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History
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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)
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Parameters
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Parameter |
Description |
variable_name |
String, enclosed in quotation marks. Name of variable to test for. |
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Usage
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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"))
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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">
<input type="Submit" name="">
</form>
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