Developing ColdFusion MX Applications with CFML
Elements of CFML

Variables

Variables are the most frequently used operands in ColdFusion expressions. Variable values can be set and reset, and can be passed as attributes to CFML tags. Variables can be passed as parameters to functions, and can replace most constants.

ColdFusion has a number of built-in variables that provide information about the server and are returned by ColdFusion tags. For a list of the ColdFusion built-in variables, see CFML Reference.

The following two characteristics classify a variable:

• The scope of the variable, which indicates where the information is available and how long the variable persists
• The data type of the variable's value, which indicates the kind of information a variable represents, such as number, string, or date

The following section lists and briefly describes the variable scopes. "Data types" lists data types (which also apply to constant values). For detailed information on ColdFusion variables, including data types, scopes, and their use, see Chapter 3, "Using ColdFusion Variables".

Variable scopes

The following table briefly lists ColdFusion variable scopes:

Scope	Description
Variables (local)	The default scope for variables of any type that are created with the cfset and cfparam tags. A local variable is available only on the page on which it is created and any included pages.
Form	The variables passed from a form page to its action page as the result of submitting the form.
URL	The parameters passed to the current page in the URL that is used to call it.
Attributes	The values passed by a calling page to a custom tag in the custom tag's attributes. Used only in custom tag pages.
Caller	A reference, available in a custom tag, to the Variables scope of the page that calls the tag. Used only in custom tag pages.
ThisTag	Variables that are specific to a custom tag, including built-in variables that provide information about the tag. Used only in custom tag pages. A nested custom tag can use the cfassociate tag to return values to the calling tag's ThisTag scope.
Request	Variables that are available to all pages, including custom tags and nested custom tags, that are processed in response to an HTTP request. Used to hold data that must be available for the duration of one HTTP request.
CGI	Environment variables identifying the context in which a page was requested. The variables available depend on the browser and server software.
Cookie	Variables maintained in a user's browser as cookies.
Client	Variables that are associated with one client. Client variables let you maintain state as a user moves from page to page in an application and are available across browser sessions.
Session	Variables that are associated with one client and persist only as long as the client maintains a session.
Application	Variables that are associated with one, named, application on a server. The cfapplication tag name attribute specifies the application name.
Server	Variables that are associated with the current ColdFusion Server. This scope lets you define variables that are available to all your ColdFusion pages, across multiple applications.
Flash	Variables sent by a Macromedia Flash movie to ColdFusion and returned by ColdFusion to the movie.
Arguments	Variables passed in a call to a user-defined function or ColdFusion component method.
This	Variables that are declared inside a ColdFusion component or in a cffunction tag that is not part of a ColdFusion component.
function local	Variables that are declared in a user-defined function and exist only while the function executes.

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