How do you tell if two variables are the same?

**Larry Serflaten** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"Harry J. Smith" <hjsmith@ix.net com.com> wrote[color=blue]
>
> How do you tell if two variables past as arguments to a subroutine are
> actually the same variable? In some languages you can compare their
> addresses. Visual Basic doesn't have pointers so what is the best way to
> do this?
>
> Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> 'MultiUI is a user defined type (Multiple-precision unsigned
> integer)
> If Z = X Then Exit Sub
> ...
> End Sub 'SetToUI[/color]

Did you try:

If Z Is X Then Exit Sub

LFS

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**Auric__** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"...And the next sign of the Apocalypse will be..."
*****
On Mon, 05 Jan 2004 18:48:46 GMT, Harry J. Smith wrote:
[color=blue]
>
>How do you tell if two variables past as arguments to a subroutine are
>actually the same variable? In some languages you can compare their
>addresses. Visual Basic doesn't have pointers so what is the best way to
>do this?
>
>Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> 'MultiUI is a user defined type (Multiple-precision unsigned
>integer)
> If Z = X Then Exit Sub
>...
>End Sub 'SetToUI[/color]

VB does indeed have pointers, they're just not well-documented. There
are three keywords that return pointers - VarPtr, StrPtr, and ObjPtr,
which return pointers to a variable, a string, and an object,
repsectively.

This code should do what you want, but it only works when args are
passed ByRef (which is the default) - if you pass them ByVal then copies
are made, each with its own address.
Public Sub SetToUI(X As MultiUI, Z As MultiUI)
Dim ptrX As Long, ptrZ As Long
ptrX = VarPtr(X)
ptrZ = VarPtr(Z)
If ptrX = ptrZ Then Exit Sub
'...
End Sub

--
auric "underscore " "underscore " "at" hotmail "dot" com
*****
Youth is not a time of life, it's a state of mind.

**Harry J. Smith** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"Larry Serflaten" <Abuse@SpamBust ers.com> wrote in message
news:3ff9e0b7$1 _7@corp.newsgro ups.com...[color=blue]
> "Harry J. Smith" <hjsmith@ix.net com.com> wrote[color=green]
> >
> > How do you tell if two variables past as arguments to a subroutine[/color][/color]
are[color=blue][color=green]
> > actually the same variable? In some languages you can compare their
> > addresses. Visual Basic doesn't have pointers so what is the best[/color][/color]
way to[color=blue][color=green]
> > do this?
> >
> > Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> > 'MultiUI is a user defined type (Multiple-precision unsigned
> > integer)
> > If Z = X Then Exit Sub
> > ...
> > End Sub 'SetToUI[/color]
>
>
> Did you try:
>
> If Z Is X Then Exit Sub
>
> LFS[/color]

Yes, but that doesn't do what I want. See the next message.

-Harry

**Harry J. Smith** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"Auric__" <not.my.real@em ail.address> wrote in message
news:4j2kvvo2tn 21lbsee88fjvbn7 9hgjp2ftq@4ax.c om...[color=blue]
> "...And the next sign of the Apocalypse will be..."
> *****
> On Mon, 05 Jan 2004 18:48:46 GMT, Harry J. Smith wrote:
>[color=green]
> >
> >How do you tell if two variables past as arguments to a subroutine[/color][/color]
are[color=blue][color=green]
> >actually the same variable? In some languages you can compare their
> >addresses. Visual Basic doesn't have pointers so what is the best way[/color][/color]
to[color=blue][color=green]
> >do this?
> >
> >Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> > 'MultiUI is a user defined type (Multiple-precision unsigned
> >integer)
> > If Z = X Then Exit Sub
> >...
> >End Sub 'SetToUI[/color]
>
> VB does indeed have pointers, they're just not well-documented. There
> are three keywords that return pointers - VarPtr, StrPtr, and ObjPtr,
> which return pointers to a variable, a string, and an object,
> repsectively.
>
> This code should do what you want, but it only works when args are
> passed ByRef (which is the default) - if you pass them ByVal then[/color]
copies[color=blue]
> are made, each with its own address.
> Public Sub SetToUI(X As MultiUI, Z As MultiUI)
> Dim ptrX As Long, ptrZ As Long
> ptrX = VarPtr(X)
> ptrZ = VarPtr(Z)
> If ptrX = ptrZ Then Exit Sub
> '...
> End Sub
>
> --
> auric "underscore " "underscore " "at" hotmail "dot" com
> *****
> Youth is not a time of life, it's a state of mind.[/color]

Sounds good, I will give it a try.

-Harry http://home.netcom.com/~hjsmith

**Harry J. Smith** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"Harry J. Smith" <hjsmith@ix.net com.com> wrote in message
news:r1ZKb.4307 6$Pg1.37238@new sread1.news.pas .earthlink.net. ..[color=blue]
>
> "Auric__" <not.my.real@em ail.address> wrote in message
> news:4j2kvvo2tn 21lbsee88fjvbn7 9hgjp2ftq@4ax.c om...[color=green]
> > "...And the next sign of the Apocalypse will be..."
> > *****
> > On Mon, 05 Jan 2004 18:48:46 GMT, Harry J. Smith wrote:
> >[color=darkred]
> > >
> > >How do you tell if two variables past as arguments to a subroutine[/color][/color]
> are[color=green][color=darkred]
> > >actually the same variable? In some languages you can compare their
> > >addresses. Visual Basic doesn't have pointers so what is the best[/color][/color][/color]
way[color=blue]
> to[color=green][color=darkred]
> > >do this?
> > >
> > >Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> > > 'MultiUI is a user defined type (Multiple-precision unsigned
> > >integer)
> > > If Z = X Then Exit Sub
> > >...
> > >End Sub 'SetToUI[/color]
> >
> > VB does indeed have pointers, they're just not well-documented.[/color][/color]
There[color=blue][color=green]
> > are three keywords that return pointers - VarPtr, StrPtr, and[/color][/color]
ObjPtr,[color=blue][color=green]
> > which return pointers to a variable, a string, and an object,
> > repsectively.
> >
> > This code should do what you want, but it only works when args are
> > passed ByRef (which is the default) - if you pass them ByVal then[/color]
> copies[color=green]
> > are made, each with its own address.
> > Public Sub SetToUI(X As MultiUI, Z As MultiUI)
> > Dim ptrX As Long, ptrZ As Long
> > ptrX = VarPtr(X)
> > ptrZ = VarPtr(Z)
> > If ptrX = ptrZ Then Exit Sub
> > '...
> > End Sub
> >
> > --
> > auric "underscore " "underscore " "at" hotmail "dot" com
> > *****
> > Youth is not a time of life, it's a state of mind.[/color]
>
> Sounds good, I will give it a try.
>
> -Harry http://home.netcom.com/~hjsmith[/color]

Works great:

Type MultiUI 'A multiple precision unsigned integer
M As Long 'Max number of super digits ever in this number
N As Long 'Current length in super digits, 1...NMax <= MuNMax
V() As Single 'Value, LSD at index 0
End Type

Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
Dim I As Long
'Subject: Re: How do you tell if two variables are the same?
'From: auric "underscore " "underscore " "at" hotmail "dot" com
'
'VB does indeed have pointers, they're just not well-documented. There
'are three keywords that return pointers - VarPtr, StrPtr, and ObjPtr,
'which return pointers to a variable, a string, and an object,
'respectively.
'
If VarPtr(Z) = VarPtr(X) Then Exit Sub
Z.N = X.N
If Z.N > Z.M Then
MuWriteErr "SetTo overflow, continuing... (N=" & _
Z.N & " > M=" & Z.M & ")"
Z.N = Z.M
End If
For I = 0 To Z.N - 1
Z.V(I) = X.V(I)
Next I
End Sub 'SetToUI

-Harry

**Larry Serflaten** · Jul 17 '05, 08:34 PM

Re: How do you tell if two variables are the same?

"Harry J. Smith" <hjsmith@ix.net com.com> wrote
[color=blue][color=green][color=darkred]
> > > Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> > > 'MultiUI is a user defined type (Multiple-precision unsigned
> > > integer)[/color][/color]
>
> Yes, but that doesn't do what I want. See the next message.[/color]

Oops, I overlooked the second line where you mentioned it was
a UDT (instead of an object) Sorry!

LFS

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**Harry J. Smith** · Jul 17 '05, 08:35 PM

Re: How do you tell if two variables are the same?

"Harry J. Smith" <hjsmith@ix.net com.com> wrote in message
news:ikiKb.3864 1$Pg1.7194@news read1.news.pas. earthlink.net.. .[color=blue]
>
> How do you tell if two variables past as arguments to a subroutine are
> actually the same variable? In some languages you can compare their
> addresses. Visual Basic doesn't have pointers so what is the best way[/color]
to[color=blue]
> do this?
>
> Public Sub SetToUI(X As MultiUI, Z As MultiUI) 'Z = X
> 'MultiUI is a user defined type (Multiple-precision unsigned
> integer)
> If Z = X Then Exit Sub
> ...
> End Sub 'SetToUI
>
> --
>
> -Harry http://home.netcom.com/~hjsmith[/color]

Now that we have pointers, how do you reference the thing that it points
to?
Like MuitiUI(ptrX) ?

Public Sub AddUI(X As MultiUI, Y As MultiUI, Z As MultiUI) 'Z = X + Y
'Sets MuErr True if overflow
Dim ptrX As Long, ptrY As Long, ptrZ As Long, tmp As Long
ptrX = VarPtr(X)
ptrY = VarPtr(Y)
ptrZ = VarPtr(Z)
If ptrZ = ptrX Then
RAddUI Y, Z
Exit Sub
ElseIf ptrZ = ptrY Then
RAddUI X, Z
Exit Sub
ElseIf X.N < Y.N Then 'If X is the smaller
tmp = prtX 'Interchange pointers
prtX = prtY
ptrY = tmp
End If
SetToUI MuitiUI(ptrX), Z 'Set Z to the larger
RAddUI MultiUI(ptrY), Z 'and add the smaller
End Sub 'AddUI

-Harry

**Auric__** · Jul 17 '05, 08:35 PM

Re: How do you tell if two variables are the same?

"...And the next sign of the Apocalypse will be..."
*****
On Thu, 08 Jan 2004 21:11:31 GMT, Harry J. Smith wrote:
[color=blue]
>Now that we have pointers, how do you reference the thing that it points
>to?
>Like MuitiUI(ptrX) ?
>
>Public Sub AddUI(X As MultiUI, Y As MultiUI, Z As MultiUI) 'Z = X + Y
>'Sets MuErr True if overflow
> Dim ptrX As Long, ptrY As Long, ptrZ As Long, tmp As Long
> ptrX = VarPtr(X)
> ptrY = VarPtr(Y)
> ptrZ = VarPtr(Z)
> If ptrZ = ptrX Then
> RAddUI Y, Z
> Exit Sub
> ElseIf ptrZ = ptrY Then
> RAddUI X, Z
> Exit Sub
> ElseIf X.N < Y.N Then 'If X is the smaller
> tmp = prtX 'Interchange pointers
> prtX = prtY
> ptrY = tmp
> End If
> SetToUI MuitiUI(ptrX), Z 'Set Z to the larger
> RAddUI MultiUI(ptrY), Z 'and add the smaller
>End Sub 'AddUI[/color]

That's a damn good question. VB isn't like C-based languages, where the
variable and its address can be used interchangeably . QuickBasic, MS's
command-line BASIC compiler, had a handful of memory functions - notable
peek and poke - but they aren't in either version of VB I have installed
(VB4 and VB6), so my guess is you'll have to use API calls. (For the
record, VB4 doesn't have VarPtr either.) I *think* CopyMemory should do
it, but that's just a guess.
--
auric "underscore " "underscore " "at" hotmail "dot" com
*****
This night methinks is but the daylight sick.

**Randy Birch** · Jul 17 '05, 08:35 PM

Re: How do you tell if two variables are the same?

: peek and poke - but they aren't in either version of VB I have installed
: (VB4 and VB6), so my guess is you'll have to use API calls. (For the
: record, VB4 doesn't have VarPtr either.) I *think* CopyMemory should do
: it, but that's just a guess.

VarPtr is a defined API in VB3 and VB4 as well, just not intrinsic as
methods within the IDE.

VB4-32
Declare Function VarPtr Lib "vb40032.dl l" (Var as Long) As Long

'VB4-16
Declare Function VarPtr Lib "vb40016.dl l" (Var as Integer) As Integer

In VB5 (if desired) the declaration is:

Declare Function VarPtr Lib "msvbvm50.d ll" (Var as Long) As Long

--

Randy Birch
MVP Visual Basic

VBnet Visual Basic Developers Resource Centre

http://vbnet.mvps.org/

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How do you tell if two variables are the same?

How do you tell if two variables are the same?

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