KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q129898: PRB: Naming Conflicts Between Variables and Objects

Article: Q129898
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0
Operating System(s): 
Keyword(s): kbprogramming kbVBp400
Last Modified: 11-JAN-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual Basic Standard Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Professional Edition, 32-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 16-bit, for Windows, version 4.0 
- Microsoft Visual Basic Enterprise Edition, 32-bit, for Windows, version 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

Conflicts between the names of various constructs produce errors in Visual Basic
version 4.0.

CAUSE
=====

Problems of this type are caused by not taking into account the scope of
variables and objects. When a conflict occurs, Visual Basic gives precedence to
constructs of a narrower scope over those of a broader scope. Some cases of this
type can be handled by Visual Basic's design time syntax checker, but others
must be handled later (called late binding) in order to permit more versatility.

RESOLUTION
==========

Use unique names for variables, objects, and other constructs whenever possible.
When this is not possible, such as with type libraries, specify a fully
qualified name (for example, OpenDialog.Help_Button) to avoid potential
conflicts.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Variables
---------

Variables have three possible levels of scope: local, module, and global. If two
variables of the same name are defined, Visual Basic uses the variable of the
narrowest scope. Therefore, by using unique names for local variables, you can
avoid a problem.

Type and Object Libraries
-------------------------

Multiple type libraries may use the same name but give different values. The
ShowHelp flag of the Common Dialog control has different values for each type of
dialog that uses it. Attempting to refer to just ShowHelp produces the
diagnostic "Ambiguous name detected" at run time.

To avoid conflicts, specify the fully qualified name of the construct, such as
FileOpenConstants.ShowHelp. The "Ambiguous name detected" topic in the Help file
describes the following other ways this message can be produced:

- More than one object in the same scope may have elements with the same name.
  Qualify the element name by including the object name and a period. For
  example:

        Object.Property

- Module-level identifiers and project-level identifiers (module names and
  referenced project names) may be reused in a procedure although it makes
  programs harder to maintain and debug. However, if you want to refer to both
  items in the same procedure, the item having wider scope must be qualified.
  For example, if MyID is declared at the module level of MyModule, and then a
  procedure-level variable is declared with the same name in the module,
  references to the module-level variable must be appropriately qualified:

         Dim MyID As String

        Sub MySub
           MyModule.MyID = "This is module-level variable"
           Dim MyID As String
           MyID = "This is the procedure-level variable"
           Debug.Print MyID
           Debug.Print MyModule.MyID
        End Sub

- An identifier declared at module level conflicts with a procedure name. For
  example, this error occurs if the variable MyID is declared at module level,
  and then a procedure is defined with the same name:

         Public MyID

        Sub MyID
           '. . .
        End Sub

  In this case, change one of the names because modification with a common
  module name would not resolve the ambiguity. Note that procedure names are
  Public by default, but variable names are Private unless specified as Public.

Form and Module Names
---------------------

Using the name of an internal function as the name of a Module, such as
String.BAS, produces no diagnostic in the IDE. Attempting to run the program
with references to the String$() functions produces the following diagnostic:

  Expected variable or procedures, not module

Because Visual Basic considers the module definition to be of narrower scope than
the internal function, it attempts to call the module as a function. Specifying
the function as VBA.String$() resolves the issue, but selecting a different
module name is the better option.

Additional query words:

======================================================================
Keywords          : kbprogramming kbVBp400 
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Version           : WINDOWS:4.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.