VarPtr() Fun

[Vincent]

I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:

Dim myArray(10) As MyObject
Dim newObject as MyObject

Set newObject = new MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

As a quick and dirty way of checking if different elements of the array
are referencing the same object, I thought I could use VarPtr like
such:

if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"

However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.

-Vincent

[Tom van Stiphout]

On 5 Jul 2006 18:36:13 -0700, "Vincent" <an**********@verizon.net>
wrote:

I would probably check the value of a unique property. Something that
in a table would get a unique index:
myArray(0).CustomerID = myArray(1).CustomerID
That way, I don't have to know and worry about VBA memory management.

-Tom.

>I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:

Dim myArray(10) As MyObject
Dim newObject as MyObject

Set newObject = new MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

As a quick and dirty way of checking if different elements of the array
are referencing the same object, I thought I could use VarPtr like
such:

if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"

However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.

-Vincent

[david epsom dot com dot au]

That is what the IS operator is for:

If MyArray(0) IS MyArray(1) then debug.print "equal"

As you have seen, VarPtr returns a pointer to the
variable, not the value of the variable.

(david)
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...

>I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:

Dim myArray(10) As MyObject
Dim newObject as MyObject

Set newObject = new MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

As a quick and dirty way of checking if different elements of the array
are referencing the same object, I thought I could use VarPtr like
such:

if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"

However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.

-Vincent

[Vincent]

That makes sense. Thanks David, I will give that a try.

-Vincent

david epsom dot com dot au wrote:

That is what the IS operator is for:

If MyArray(0) IS MyArray(1) then debug.print "equal"

As you have seen, VarPtr returns a pointer to the
variable, not the value of the variable.

(david)
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...

I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:

Dim myArray(10) As MyObject
Dim newObject as MyObject

Set newObject = new MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

As a quick and dirty way of checking if different elements of the array
are referencing the same object, I thought I could use VarPtr like
such:

if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"

However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.

-Vincent

[Terry Kreft]

As david says you should use the Is operator but if you do want the pointer
to an object you should be using objptr, not varptr, and BTW the pointer to
a string variable is strptr.

so
Dim myArray(10) As MyObject
Dim newObject As MyObject

Set newObject = New MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

If ObjPtr(myArray(0)) = ObjPtr(myArray(1)) Then
Debug.Print "yep"
End If

If myArray(0) Is myArray(1) Then
Debug.Print "yep2"
End If

Set myArray(0) = Nothing
Set myArray(1) = Nothing
Set newObject = Nothing
Prints
yep
yep2

From MSDN (Q199824)
VarPtr - Returns the address of a variable.
VarPtrArray - Returns the address of an array.
StrPtr - Returns the address of the UNICODE string buffer.
VarPtrStringArray - Returns the address of an array of strings.
ObjPtr - Returns the pointer to the interface referenced by an object
variable.

It might be an idea to look at http://vb.mvps.org/hardcore/ or try and get
hold of a hard copy.
--

Terry Kreft
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...

That makes sense. Thanks David, I will give that a try.

-Vincent

david epsom dot com dot au wrote:

That is what the IS operator is for:

If MyArray(0) IS MyArray(1) then debug.print "equal"

As you have seen, VarPtr returns a pointer to the
variable, not the value of the variable.

(david)
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...

>I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:
>
Dim myArray(10) As MyObject
Dim newObject as MyObject
>
Set newObject = new MyObject
>
Set myArray(0) = newObject
Set myArray(1) = newObject
>
As a quick and dirty way of checking if different elements of the

array

are referencing the same object, I thought I could use VarPtr like
such:
>
if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"
>
However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.
>
-Vincent
>

[Vincent]

Thanks Terry, I did not realize there was a separate function for what
I was trying to do.

-Vincent

Terry Kreft wrote:

As david says you should use the Is operator but if you do want the pointer
to an object you should be using objptr, not varptr, and BTW the pointer to
a string variable is strptr.

so
Dim myArray(10) As MyObject
Dim newObject As MyObject

Set newObject = New MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

If ObjPtr(myArray(0)) = ObjPtr(myArray(1)) Then
Debug.Print "yep"
End If

If myArray(0) Is myArray(1) Then
Debug.Print "yep2"
End If

Set myArray(0) = Nothing
Set myArray(1) = Nothing
Set newObject = Nothing
Prints
yep
yep2

From MSDN (Q199824)
VarPtr - Returns the address of a variable.
VarPtrArray - Returns the address of an array.
StrPtr - Returns the address of the UNICODE string buffer.
VarPtrStringArray - Returns the address of an array of strings.
ObjPtr - Returns the pointer to the interface referenced by an object
variable.

It might be an idea to look at http://vb.mvps.org/hardcore/ or try and get
hold of a hard copy.
--

Terry Kreft
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...

That makes sense. Thanks David, I will give that a try.

-Vincent

david epsom dot com dot au wrote:

That is what the IS operator is for:
>
If MyArray(0) IS MyArray(1) then debug.print "equal"
>
As you have seen, VarPtr returns a pointer to the
variable, not the value of the variable.
>
(david)
>
>
"Vincent" <an**********@verizon.netwrote in message
news:11**********************@v61g2000cwv.googlegr oups.com...
I have a couple of questions about the VarPtr() function of VBA. I
have created my own class, lets call it MyObject and in one of my
modules, I have declared an array of type MyObject. In my array, i
wish to store one or more references to the same instantiation of a
MyObject object. So, I have something like this:

Dim myArray(10) As MyObject
Dim newObject as MyObject

Set newObject = new MyObject

Set myArray(0) = newObject
Set myArray(1) = newObject

As a quick and dirty way of checking if different elements of the

array

are referencing the same object, I thought I could use VarPtr like
such:

if(VarPtr(myArray(0)) = VarPtr(myArray(1))) then debug.print "Objects
equal"

However, in this instance, VarPtr seems to be returning the address of
the myArray variable and not the address of the MyObject that was
stored in the array. How do I retrieve the address of the MyObject
that was stored in the array? Or, is this a hopless endeavor better
suited to C programming? Thanks for your help.

-Vincent