Q126780: PRB: Operator/Operand Type Mismatch When Comparing Two Objects

Article: Q126780
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): kbcode kberrmsg
Last Modified: 12-FEB-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, version 3.0 
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SYMPTOMS
========

The 'Operator/Operand Type Mismatch' error is returned when comparing two
objects with the equal sign (=) operator.

CAUSE
=====

The equal sign operator is used to compare character, logical, date, or numeric
data. When the variable is an object reference, the equal sign is the assignment
operator. The equal sign is used to create a reference to an object. It should
not be used to compare objects.

WORKAROUND
==========

Use the COMPOBJ() function to compare two objects. The COMPOBJ() function
compares the properties of an object. It returns .T. if the properties and
property values of two objects are identical.

STATUS
======

This behavior is by design.

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

The following example illustrates the use of the COMPOBJ() function. It compares
two objects created with the SCATTER NAME command. To run this example, copy the
following code into a new program file (*.PRG) and run it.

     USE SYS(2004)+'\samples\data\customer'
     SCATTER NAME ocust1   && Creates a custom object ocust1
     SCATTER NAME ocust2   && Creates a custom object ocust2
     Ccompare=IIF(COMPOBJ(ocust1,ocust2),'True','False')
     * Test if objects are identical
     WAIT WINDOW "Compobject returned " + Ccompare

NOTE: Classes have default properties that can be set when an object is
instantiated. For example, when a form is instantiated, the values of CAPTION
and NAME properties, among other properties, are set to a unique value. The
following example illustrates the fact that COMPOBJ() will return .F. if the
values of these properties are not modified. Use the AMEMBERS() function to
verify the names and infer the values of properties, procedures, and member
objects of an object.

     frmtest1= CREATEOBJECT('form')  && Creates an instance of a form
     frmtest2 = CREATEOBJECT('form') && Creates an instance of a form
     Compare= IIF(COMPOBJ(frmtest1,frmtest2),'True','False')
     WAIT WINDOW "Compobj returned " + Compare
     * In this case, COMPOBJ returned .F. Some property values are not
     * identical

     ? frmtest1.name   && Returns Form<n>, where n is a number
     ? frmtest2.name   && Returns Form<n+1>, where n is a number
     frmtest1.name="mytest"
     frmtest2.name="mytest"
     ? frmtest1.caption && Returns Form<n>, where n is a number
     ? frmtest2.caption && Returns Form<n+1>, where n is a number

     frmtest1.caption= "This is a test"
     frmtest2.caption= "This is a test"
     ?COMPOBJ(frmtest1,frmtest2)  && Returns .T.

Additional query words: VFoxWin errmsg err msg

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Keywords          : kbcode kberrmsg 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300
Version           : WINDOWS:3.0

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