VBA - advanced videos | Excel VBA Part 43.2 - ByRef and ByVal (When to use Parentheses)

Posted by Andrew Gould on 24 October 2016

When to use parentheses (round brackets) is one of the apparently annoyingly inconsistent features of VBA. There are some clearly defined rules which dictate when you should and shouldn't use parentheses and this video attempts to explain them!

You can increase the size of the video:

Full screen mode for YouTube

You can view the video in full screen mode as shown on the left, using the icon at the bottom right of the frame.

You can also increase the quality of the video:

Changing resolution

You can improve the resolution of the video using another icon at the bottom right of the frame. This will slow down the connection speed, but increase the display and sound quality. This icon only becomes visible when you start playing the video.

Finally, if nothing happens when you play the video, check that you're not using IE in compatibility view.

This page has 2 threads Add post
duggie   Reply to duggieReply
11 Jun 18 at 17:37

Andrew,

We know "usually" the default for passing arguments is by reference, so if the keyword ByRef / ByVal is omitted, the argument will be passed by reference.

In a standard module, this can (and has been) easily proved.

However, I have yet to see an example to prove the case fro a Get / Let / Set Property.

Do these properties also behave in the same way, ie the default is by reference? The reason for my query is if you create a Let Property using Insert -> Procedure -> Property, the keyworb, ByVal, is automatically added.

Does that mean for a Let Property (and I assume also for a Set Property), the default, perhaps the ONLY way to pass arguments is by value?

Is it possible to prove this by way of an example?

Also what about Get Properties? Do they pass by reference by default or by value?

Thanks

Andrew G   Reply to Andrew GReply
12 Jun 18 at 09:11

Good question!  And yes, you're right: passing arguments to Property Let and Property Set procedures passes ByVal, even if you specify ByRef http://excelmatters.com/2016/03/15/when-is-byref-not-byref/

You can test this using the VarPtr function https://bytecomb.com/vba-internals-getting-pointers/

You can start with an example using simple subroutines in a regular module:

Sub AssignNumber()

    Dim a As Long
    
    a = 1
    Debug.Print "a = ", a, VarPtr(a)
    
    IncreaseNumber a
    Debug.Print "a = ", a, VarPtr(a)
    
End Sub

Sub IncreaseNumber(ByVal b As Long)

    b = b + 1
    Debug.Print "b = ", b, VarPtr(b)
    
End Sub

When passing the argument ByVal, your output in the Immediate window will resemble this:

a =            1             11923696 
b =            2             11923688 
a =            1             11923696

The return value of the VarPtr function will be different for a and b.

If you change the signature of the IncreaseNumber procedure to pass ByRef:

Sub IncreaseNumber(ByRef b As Long)

The output will reseble this:

a =            1             11923696 
b =            2             11923696 
a =            2             11923696

The return value of the VarPtr function will be the same for a and b.

You can try the same test with a Property Let procedure (the example below uses a class module called MyClass although you can write the property in a normal module if you prefer):

Public Property Let MyProperty(ByVal d As Long)

    d = d + 1    
    Debug.Print "d = ", d, VarPtr(d)
    
End Property

Add another procedure in a regular module which assigns a value to this property:

Sub TestMyClass()

    Dim mc As New MyClass
    Dim c As Long
    
    c = 1
    Debug.Print "c = ", c, VarPtr(c)
    
    mc.MyProperty = c
    
    Debug.Print "c = ", c, VarPtr(c)
    
End Sub

With ByVal or ByRef, the VarPtr function will always show a different result for c and d:

c =            1             11923692 
d =            2             11923688 
c =            1             11923692

Sorry for the long answer.  Hope it helps!

duggie   Reply to duggieReply
12 Jun 18 at 10:50

Andrew,

Thanks for your detailed reply.

I can't say I am familiar with the VarPtr function but the values that the vaiables c and d returned (1, 2, 1) and (1, 2, 1), whether you pass ByVal or ByRef, was enough to convince me that no matter what you write, Let Properties always pass by value.

Can you confirm that for the Get Property too with an example?

Thanks

 

Andrew G  
13 Jun 18 at 06:58

Property Get procedures do actually honour your ByRef/ByVal setting.  You can demonstrate this in a similar way.  Here's a simple property in a class module called MyClass:

Public Property Get MyProperty(ByVal b As Long) As Long

    b = b + 1
    
    Debug.Print "b = ", b, VarPtr(b)
    
    MyProperty = b
    
End Property

Here's a test procedure in a normal module:

Sub TestMyClass()

    Dim mc As New MyClass
    Dim a As Long
    
    a = 1
    
    Debug.Print "a = ", a, VarPtr(a)
    
    Debug.Print "mc.MyProperty = ", mc.MyProperty(a)
    
    Debug.Print "a = ", a, VarPtr(a)
    
End Sub

Running the test procedure using ByVal returns something resembling this:

a =            1             45478828 
b =            2             45478816 
mc.MyProperty =              2 
a =            1             45478828 

And with ByRef:

a =            1             45478828 
b =            2             45478828 
mc.MyProperty =              2 
a =            2             45478828 

I hope that helps!

Andrew G  
13 Jun 18 at 11:34

No problem, happy that it helped!

duggie  
13 Jun 18 at 10:07

Many thanks, I can sleep better now!

ryan051788   Reply to ryan051788Reply
10 Jun 18 at 02:40

Hi there,

I tried to do the same as what you have here on your tutorial. I just cannot find out why on the calculation of time lengths for the movies, the last row of result is showing #N/A error for me.

The file is here: https://www.dropbox.com/s/kl6yonheorqocm6/VBA%20Arrays%20sample%20with%20calculation.xlsm?dl=0

 

Can you please check my code?

Option Explicit

Sub CalculateWithArray()

    Dim FilmLengths() As Variant
    Dim Answers() As Variant
    Dim Dimension1 As Long, Counter As Long
    
    Sheet1.Activate
    
    Range("f3", Range("g3").End(xlDown)).ClearContents
    
    ' Assign values of range D to the array FilmLengths
    FilmLengths = Range("d3", Range("d3").End(xlDown))
    ' Assign the number of values of array FilmLengths to the variable Dimension1
    Dimension1 = UBound(FilmLengths, 1)
    ' Resize the dimensions of array Answers according to the number of values of Array FilmLenghts and add 2nd column or dimension
    ReDim Answers(1 To Dimension1, 1 To 2)
    ' Loop over the FilmLengths and return Answers as number of hours and remainder in minutes
    For Counter = 1 To Dimension1
            Answers(Counter, 1) = Int(FilmLengths(Counter, 1) / 60)
            Answers(Counter, 2) = FilmLengths(Counter, 1) Mod 60
    Next Counter
    ' Populate columns F and G with the Answers
    Range("f3", Range("f3").Offset(Counter - 1, 1)) = Answers
    
    Erase FilmLengths
    Erase Answers

End Sub
 

 

Thank you and regards,

 

Ryan

Andrew G   Reply to Andrew GReply
11 Jun 18 at 08:19

Hi Ryan,

The problem is caused by this line near the end of your code:

Range("f3", Range("f3").Offset(Counter - 1, 1)) = Answers

Try changing it to this:

Range("f3", Range("f3").Offset(Dimension1 - 1, 1)) = Answers

The reason you're encountering the problem is because the variable you use to iterate through a For Next loop has a final value that is one greater than the To value you provide.  So, if your loop looks like this:

For Counter = 1 To 3
    'do something
Next Counter

Counter will have a value of 4 when the loop has finished.

I hope that helps!

ryan051788   Reply to ryan051788Reply
11 Jun 18 at 08:17

I have found the error. I was using the wrong variable.

Thanks.

Andrew G   Reply to Andrew GReply
11 Jun 18 at 08:21

Ahh you beat me to it as I was writing a reply!  Oh well, it's always more satisfying when you solve a problem by yourself!

Add a new post