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Levels of Scope

Just as the scope of a variable depends on where and how it is declared, the scope of a watch depends on the manner of its definition. Specifying the scope of a watch determines the context in which its behavior is observed. If you know where in your program the observation of a variable is significant, you can make more efficient use of your debugging time by specifying the appropriate Watch context.

You are already familiar with the issue of scope as it pertains to data variables. In a block-structured programming language such as Visual Basic, the visibility of a variable depends on where it is declared. A variable may exist at any one of the following three levels of scope:

A variable declared in the context of a particular procedure is visible only in the context of that procedure. It is said to be local in its scope, which means that it is invisible to all other procedures in the program. Consider the following subprocedures, for instance:

Sub MyProcedure
Dim iCount as Integer, sName as String
‘ pretend that something useful happens later in the
åprocedure
End Sub
Sub YourProcedure
Dim iCount as Integer
‘ pretend that something else useful happens here, too
End Sub

The variables declared in these routines are all local in scope. The variable sName declared in MyProcedure can be accessed only by the code in MyProcedure. It is not visible to YourProcedure, nor is it visible to any other routine in the program. The two iCount variables are each local to the procedures in which they are declared. They are permitted to have the same name because each is unique in the context of the procedure in which it is declared.

A variable may also have module scope if it is declared in the General Declaration section of its code module using the keyword Private. In this case, the variable is visible to all procedures contained in the module, but it is invisible to all other procedures in the program.

Finally, a variable is global in scope if it is declared in the General Declaration section of its code module using the keyword Public. Such a variable is visible to all procedures contained throughout the program.

If you already understand how variables may have their scope defined at these different levels, you will find the scope of a watch fairly easy to understand. Just as a variable’s scope may be at the local, module, or global level, the scope of a watch may be defined at these levels too.


  

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