Microsoft KB Archive/130833

= How to Find If Two Object Variables Refer to One Instance =

Article ID: 130833

Article Last Modified on 2/15/2000

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APPLIES TO


 * Microsoft Visual FoxPro 3.0 Standard Edition

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This article was previously published under Q130833



SUMMARY
This article provides a way to compare two object variables and verify whether they are two different instances of a class or a pointer to the same object.



MORE INFORMATION
Although the equal sign operator (=) is usually used to compare data, it is the assignment operator for object type variables. Using the equal sign creates a reference to an object. For example: oObj1=CREATEOBJECT('Custom') && Creates an instance of the Custom class oObj2=oObj1                 && Creates a reference to oObj1 The same object can be modified through the oObj1 or the oObj2 references.

There is no Visual FoxPro function you can use to see if two variables are pointing to the same object or if they are two different instances. However, you can build a user-defined function to do it.

The following example code provides a user-defined function that compares two variables. The function returns false (.F.) if the two variables do not point to the same object, and it returns true (.T.) if one variable is a reference to the other variable. The two variables point to the same object if modifying a property of one object reference affects the other object variable. If the value is not affected, then the two object variables represent two different instances.

Sample code
oObj1=CREATEOBJECT('Custom') oObj2=CREATEOBJECT('Custom') oObj3=oObj1 ? SameObj(oObj1,oObj2) ? SameObj(oObj1,oObj3) RETURN

FUNCTION SameObj(oObject1,oObject2) LOCAL lcObjName1,lcTempObjName,llMatch

IF NOT COMPOBJ(oObject1,oObject2) RETURN .F. ENDIF lcObjName1=oObject1.Name oObject1.Name='_'+lcObjName1 llMatch=(oObject1.Name==oObject2.Name) oObject1.Name=lcObjName1 RETURN llMatch

Additional query words: VFoxWin

Keywords: kbcode KB130833

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