Q129940: PRB: Out of Stack Space Error Caused by Property Procedure

Article: Q129940
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 11-JAN-2001

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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 
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SYMPTOMS
========

Using a non-reserved Visual Basic keyword within a Property Procedure of the
same name creates a recursive call to that Property statement resulting in this
error:

  Out of Stack Space Error.

CAUSE
=====

Visual Basic allows you to define Properties and Methods that have the same name
as non-reserved keywords because many keywords (such as Left) in previous
versions of Visual Basic are used frequently by OLE servers. If you take
advantage of this in your own Class, an "Out of Stack Space error" can occur in
a Property Get Procedure when both of the following conditions are met:

- A call to the non-reserved keyword with the same name as the Property is
  located within a Property Get Procedure.

- The Property Get Procedure returns a Variant or Object.

RESOLUTION
==========

Typically, if one of the following conditions is true, Visual Basic can
determine whether to call the Property Get procedure or the non-reserved
keyword:

- The Property Get procedure doesn't return a Variant or Object.

-or-

- The call to the non-reserved keyword takes a different number of parameters
  then the Property Get procedure takes.

For example, given the following Property Get Property procedure, the Visual
Basic Left function would be called instead of the Property Get procedure:

     Property Get Left() as String
        Left = Left("Hello World",10)  ' Visual Basic Left function called
     End Property

Because the Property Get Procedure expects 0 parameters and the Visual Basic
function expects 2, the Visual Basic Left function is called.

If, however, the Property Get Procedure returns either a Variant or an Object,
the Property Get Procedure is called, regardless of the number of Parameters the
Property Procedure expects. This occurs because Objects, which are now supported
in Variants, can have a default property, which can take parameters themselves.
When you call a function that returns a Variant or Object, and you pass the
incorrect number of parameters, Visual Basic realizes that you intended to pass
the parameters to the default property of the Object, so it generates a call to
the default property with those parameters. In this case, the "Incorrect Number
of Parameters" message is not generated because it is not necessarily known how
many parameters are expected by the default property.

STATUS
======

This behavior is by design.

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

Steps to Reproduce Behavior
---------------------------

1. Start a new project in Visual Basic. Form1 is created by default.

2. Add a Command Button (Command1) to Form1.

3. Add the following code to the Command1_Click procedure:

     Sub Command1_Click()
        Dim clsClass1 As New Class1
        MsgBox clsClass1.Left
     End Sub

4. Insert a Class Module (Class1) by choosing Class Module from the Insert Menu
  (ALT, I, C).

5. Add the following code to the Class1 module:

     Property Get Left() ' This returns a Variant by default
        Const cTempStr = "Summer"
        Left = Left(cTempStr, 3)
     End Property

6. Press the F5 key to run the program.

7. Click the Command1 button. An 'Out of Stack Space' Error message appears at
  this point, where you might expect to see a Message Box with the phrase
  "Sum."

Additional query words: 4.00 vb4win vb4all

======================================================================
Keywords          :  
Technology        : kbVBSearch kbAudDeveloper kbVB400Search kbVB400 kbVB16bitSearch
Issue type        : kbprb

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