Example - Variable Scope in Procedures

VBScript Tutorials - Herong's Tutorial Examples

∟Example - Variable Scope in Procedures

This section provides a tutorial example on validating scope of global variables in the main code and local variables in procedures.

To help you understand variable scope concepts, I wrote the following sample code, function_variable_scope.html:

<html>
<body>
<!-- function_variable_scope.html
 - Copyright (c) 1998 HerongYang.com. All Rights Reserved.
-->
<pre>
<script language="vbscript">
   Dim vGlobalDim
   vGlobalDim = "Cat"
   vGlobalNoDim = "Dog"

   Dim vTempDim
   vTempDim = "Bird"
   vTempNoDim = "Fish"

   Call ScopeCheck()

   document.writeln("")
   document.writeln("Current value after Sub:")
   document.writeln("   vGlobalDim = " & vGlobalDim)
   document.writeln("   vGlobalNoDim = " & vGlobalNoDim)
   document.writeln("   vLocalDim = " & vLocalDim)
   document.writeln("   vLocalNoDim = " & vLocalNoDim)
   document.writeln("   vTempDim = " & vTempDim)
   document.writeln("   vTempNoDim = " & vTempNoDim)

Sub ScopeCheck()
   Dim vLocalDim
   vLocalDim = "Apple"
   vLocalNoDim = "Orange"

   Dim vTempDim
   vTempDim = "Banana"
   vTempNoDim = "Grape"
   
'  Updating values
   vGlobalDim = vGlobalDim & " - Updated by Sub"
   vGlobalNoDim = vGlobalNoDim & " - Updated by Sub"
   vLocalDim = vLocalDim & " - Updated by Sub"
   vLocalNoDim = vLocalNoDim & " - Updated by Sub"
   vTempDim = vTempDim & " - Updated by Sub"
   vTempNoDim = vTempNoDim & " - Updated by Sub"

'  Showing values
   document.writeln("")
   document.writeln("Current value in Sub:")
   document.writeln("   vGlobalDim = " & vGlobalDim)
   document.writeln("   vGlobalNoDim = " & vGlobalNoDim)
   document.writeln("   vLocalDim = " & vLocalDim)
   document.writeln("   vLocalNoDim = " & vLocalNoDim)
   document.writeln("   vTempDim = " & vTempDim)
   document.writeln("   vTempNoDim = " & vTempNoDim)
End Sub
</script>
</pre>
</body>
</html>

Here is the output:


Current value in Sub:
   vGlobalDim = Cat - Updated by Sub
   vGlobalNoDim = Dog - Updated by Sub
   vLocalDim = Apple - Updated by Sub
   vLocalNoDim = Orange - Updated by Sub
   vTempDim = Banana - Updated by Sub
   vTempNoDim = Grape - Updated by Sub

Current value after Sub:
   vGlobalDim = Cat - Updated by Sub
   vGlobalNoDim = Dog - Updated by Sub
   vLocalDim = 
   vLocalNoDim = 
   vTempDim = Bird
   vTempNoDim = Grape - Updated by Sub

Here are my comments about this example:

There are 6 variables in this example: vGlobalDim, vGlobalNoDim, vLocalDim, vLocalNoDim, vTempDim, and vTempNoDim.
The behavior of vGlobalDim and vGlobalNoDim is pretty consistent, defined in the main code; and accessible in the procedure. "Dim" or not makes no difference.
The behavior of vLocalDim and vLocalNoDim is also consistent, define in the procedure, not accessible in the main code. Notice that vLocalDim and vLocalNoDim are empty in the "after Sub" message.
The behavior of vTempDim and vTempNoDim shows that "Dim" statement forces vTempDim to a new local variable. So we have two variables of the same name, one in the main code, and one in the procedure. This is why vTempDim still has the old value after the subroutine call.