Using scopes

The following sections provide details on how you can create and use variables in different scopes.

Evaluating unscoped variables

If you use a variable name without a scope prefix, ColdFusion checks the scopes in the following order to find the variable:

  1. Local (function-local, UDFs and CFCs only)

  2. Arguments

  3. Thread local (inside threads only)

  4. Query (not a true scope; variables in query loops)

  5. Thread

  6. Variables

  7. CGI

  8. Cffile

  9. URL

  10. Form

  11. Cookie

  12. Client

Because ColdFusion must search for variables when you do not specify the scope, you can improve performance by specifying the scope for all variables.

To access variables in all other scopes, you must prefix the variable name with the scope identifier.

Scopes and CFX tags

ColdFusion scopes do not apply to ColdFusion Extension (CFX) tags, custom tags that you write in a programming language such as C++ or Java. The ColdFusion page that calls a CFX tag must use tag attributes to pass data to the CFX tag. The CFX tag must use the Java Request and Response interfaces or the C++ Request class to get and return data.

The Java setVariable Response interface method and C++ CCFX::SetVariable method return data to the Variables scope of the calling page. Therefore, they are equivalent to setting a Caller scope variable in a custom ColdFusion tag.

Using scopes as structures

ColdFusion makes all named scopes available as structures. You cannot access the function-local scope for user-defined functions (UDFs) that you define using CFScript as a structure.

You can reference the variables in named scopes as elements of a structure. To do so, specify the scope name as the structure name and the variable name as the key. For example, if you have a MyVar variable in the Request scope, you can reference it in either of the following ways:

Request.MyVar 
Request["MyVar"]

Similarly, you can use CFML structure functions to manipulate the contents of the scope. For more information on using structures, see Using Arrays and Structures.

Important: Do not call StructClear(Session) to clear session variables. This deletes the SessionID, CFID, and CFtoken built-in variables, effectively ending the session. If you want to use StructClear to delete your application variables, place those variables in a structure in the Session scope, and then clear that structure. For example, place all your application variables in Session.MyVars and then call StructClear(Session.MyVars) to clear the variables.