Variable and Constant Scope

The scope of a variable or a constant determines whether the variable or the constant is known to only one procedure, all procedures in a module, or all procedures in your database. You can create variables or constants that can be used by any procedure in your database (public scope). You can also create variables or constants that apply only to the procedures in a module or only to a single procedure (private scope). A variable declared inside a procedure is always private to that procedure (available only within the procedure). A variable declared in the Declarations section of a module can be private (available only to the procedures in the module) or public. You can pass values from one procedure to another using a parameter list, but the values might be held in variables having different names in the two procedures. See the sections on the Function, Sub, and Call statements later in this tutorial.

To declare a public variable, use the Public statement in the Declarations section of a standard module or a class module. All modules attached to forms or reports are class modules. To declare a public constant, use the Public keyword with a Const statement in the Declarations section of a standard module. You cannot declare a public constant in a class module. To declare a variable or a constant that all procedures in a module can reference, define that variable or constant in the Declarations section of the module. (A variable defined in a Declarations section is private to the module unless you use the Public statement.) To declare a variable or a constant used only in a particular procedure, define that variable or constant as part of the procedure.

Visual Basic in Access 2010 allows you to use the same name for variables or constants in different module objects or at different levels of scope. In addition, you can declare constants and public variables in form and report modules as well as public variables and constants in standard modules. (You can declare a constant in a form or report module, but it cannot be public.)

To use the same name for public variables and constants in different module objects or form or report modules, specify the name of the module to which it belongs when you refer to it. For example, you can declare a public variable named intX in a module object with the name modMyModule and then declare another public variable named intX in a second module object, named modMyOtherModule. If you want to reference the intX variable in modMyModule from a procedure in modMyOtherModule (or any module other than modMyModule), you must use the following code:

You can also declare variables or constants with the same name at different levels of scope within a module object or a form or report module. For example, you can declare a public variable named intX and then declare a local variable named intX within a procedure. (You can't declare a public variable within a procedure.) References to intX within the procedure refer to the local variable, while references to intX outside the procedure refer to the public variable. To refer to the public variable from within the procedure, qualify it with the name of the module, just as you would refer to a public variable from within a different module.

Declaring a public variable in a form or report module can be useful for variables that are logically associated with a particular form or report but that you might also want to use elsewhere. Like the looser naming restrictions, however, this feature can sometimes create confusion. In general, it's still a good idea to keep common public variables and constants in standard modules and to give public variables and constants names that are unique across all variable names in your application.