PRB: Operator/Operand Type Mismatch When Comparing Two Objects

ID: Q126780

3.00 WINDOWS

  kbprb

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0

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 reference words: VFoxWin 3.00 errmsg err msg

KBCategory:   kbprb

KBSubcategory: FxprgGeneral

Keywords          : kbcode kberrmsg FxprgGeneral 
Version           : 3.00
Platform          : WINDOWS