Some aspects of scoping in Basic depend on the library structure. This section describes which variables declared in a Basic source code module are seen from what libraries or modules. Generally, only variables declared outside Subs are affected by this issue. Variables declared inside Subs are local to the Sub and not accessible from outside of the Sub. For example:
Option Explicit ' Forces declaration of variables Sub Main Dim a% a% = 42 ' Ok NotMain() End Sub Sub NotMain a% = 42 ' Runtime Error "Variable not defined" End Sub
Variables can also be declared outside of Subs. Then their scope includes at least the module they are declared in. To declare variables outside the Subs, the commands
Global are used.
Private command is used to declare variables that can only be used locally in a module. If the same variable is declared as
Private in two different modules, they are used independently in each module. For example:
Library Standard, Module1:
Private x As Double Sub Main x = 47.11 ' Initialize x of Module1 Module2_InitX ' Initialize x of Module2 MsgBox x ' Displays the x of Module1 Module2_ShowX ' Displays the x of Module2 End Sub
Library Standard, Module2:
Private x As Double Sub Module2_InitX x = 47.12 ' Initialize x of Module2 End Sub Sub Module2_ShowX MsgBox x ' Displays the x of Module2 End Sub
Main in Module1 is executed,
47.11 is displayed (
x of Module1) and then
x of Module2).
Dim commands declare variables that can also be accessed from outside the module. They are identical in this context. Variables declared with
Dim can be accessed from all modules that belong to the same library container. For example, based on the library structure shown in Illustration 12.39: Sample module structure, any variable declared with
Dim in the Application Basic Modules Standard/Module1, Standard/Module2, Library1/Module1, Library1/Module2 can also be accessed from all of these modules, therefore the library container represents the logical root scope.
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