vbNullString

[Digitborn.com]

Hello,

What's the difference when you use vbNullString or "". For example:

TextBox1.Text = " "
TextBox1.Text = "vbNullString"

Are you saving memory or anything else?

 

[sijpie]

Yes - to your Minor Point.

 

[DocAElstein]

Hi

Yes - to your Minor Point.

Thanks sijpie.

_ ...................
P.s. A couple of Threads running in parallel have some interesting discussions along the lines of variable declarations “referring to pointers“ or Pigeon holes with an ( initial) or start Address etc...
http://www.mrexcel.com/forum/excel-questions/917689-passing-array-class-byval-byref.html
http://www.mrexcel.com/forum/excel-questions/917675-passing-objects-byref-byval.html

_.. Interesting one learns initially the idea of a declaration of a variable as setting aside the appropriate space in computer memory. Then as we get into more detail that only appears, if at all, to be for things like numbers.

 

[RoryA]

Some people say that

If Len(sStr) = 0 Then

is the fastest way. With a simple time test loop I found that for VBA this is not the case. I think that this is because as I mention above, testing for vbNullString only involves checking if the address is the same as vbNullstring address, whereas testing the length involves more steps

As a matter of interest, what was your test code? Unless you know that your variable was never assigned a value, or was cleared explicitly using vbNullString, I'd be surprised if you see greater efficiency using vbNullString since the address will not be the same - i.e. StrPtr won't return 0 for your variable.

As best I recall the last time I looked at it, you're talking hundredths of a second to do 1m comparisons whichever way you choose, so I'll probably save myself some typing.

I also don't believe that explicitly setting objects to nothing will resolve any memory leaks you might experience - that doesn't actually trigger garbage collection directly.

 

[DocAElstein]

@Rory and sijpie

As a matter of interest, what was your test code? .....

In all these considerations i am still not usually seeing any consideration of “....what about Empty......“ ( from about posts # 15 ) and using that instead for the comparison. I mean my basic ideas ( for my stuff ) was to “get rid of stuff” in an Array that i did now want using
= Empty
Then correspondingly i do a
If ______ = Empty

An alternative would be to first do the
= Empty,
Then
= vbNullString
And then do a
If ______ = vbNullString ____ ( or If Len(_____) = 0 _____

... but maybe i see the point it may all be splitting hairs a bit, but if anyone did happen to do any speed tests, i would be interested if an additional
= Empty
could be done.

Note the point my experiments showed that you can do a
= Empty
check against Strings, Longs and even Objects etc, and for the corresponding..... “not here”, “zero length”, “not being anything”, “Not having an address of where something actually is “ , ( or “WTF existence is Not being !?” ) ..... a True is returned... convenient for checking things that may be of different types.. maybe..

Alan

 

[RoryA]

Empty is a Variant subtype. If you use = Empty, the compiler will have to create a variable of the relevant type and then perform the comparison. (the appropriate test for a variant is IsEmpty)

Also, FYI, vbNull is a constant with value 1 - it is not any kind of null/nullable data type.

 

[DocAElstein]

Hi Rory,
Thanks for the reply..

...vbNull is a constant with value 1 - it is not any kind of null/nullable....

Thanks for clearing that up. It was looking as though that was what it was.. but I could not google anything to clarify that. So I can ignore it in consideration of Null / Nothing Empty stuff. Saves me looking further.
_....

Empty is a Variant subtype. If you use = Empty, the compiler will have to create a variable of the relevant type and then perform the comparison. (the appropriate test for a variant is IsEmpty)...

I see now I was doing something a bit stupid. As you said, = Empty was making a relevant type for the comparison. So I am fooling myself a bit using it as a check for the relevant type of “Null”, “Not there”, “or “what the Not nothing Not there where wotever” .
And I just saw that doing the
If IsEmpty(________) ____
On a Variable type other than a Variant which is vbNullString, = “”, 0 or whatever, does not indeed give me True

But if speed was not too important it could still be a possibility, for the case of my Variant Variables.

But the better thing to do would be ( for the Variant Variable case ) to empty them with
= Empty,
Then do any comparison with
If IsEmpty(____)

So there still may be some worth in doing some comparison speed tests, but probably again splitting hairs a bit.

The comparison i guess would then be what is quicker. ( For the variant Variable case )

_A)
Put
= Empty
Do
If IsEmpty(____)

_B)
Put
= Empty
Do
= vbNullString ( or one of the other Null”, “Not there”, “or “what the Not nothing Not there wotever” )

Do
If _______ = vbNullString ( or the appropriate other “of the other Null”, “Not there”, “or “what the Not nothing Not there wotever” )



Thanks
Alan

P.s. BTW Do you ( or anyone ) happen to know the answer to that?. I guess A) should be quicker than B).
I will have a go sometime anyway when I get the time.

 

[RoryA]

B would require you to know what was inside the Variant at design time.

 

[DocAElstein]

Hi

B would require you to know what was inside the Variant at design time.

I did not think "trashing" stuff would make any difference as to what was in the Element of variant type in an Array ( Data Field of variant types ) . I guess it works like deleting files then , takes a bit longer if they are big?
In my case there would ( for now ) most likely just be strings of text, not more than about 100 characters in some Elements and i do not want them long text strings ( as i will paste the whole Array out again in one go ), and the Variant Elements which I did not want to “empty” would have shorter text like “100 mg” or similar. What i do is copy a big list from something like a web site to the clipboard, paste it in a spare sheet, then apply a code which captures the values in one go from the pasted in selection. It then loops through the Array, picks out what i want and empties the Elements with stuff in that I do not want. ( I then further strip everything I do want down to a simple number with the same units and so need no unit qualifier – keeps the data nice and simple! So here 100 mg becomes O.1 ) )


At the end of the day, time may not be really a big issue. I just thought before i start doing it big time i would check out the best way to do it. And also i wanted to get clear in me head the different “ not having stuff in etc.. “ things. Clearly i had some dopey ideas about Empty.
But i think i have almost got that one now.

I just had the gut feeling that using Variant Elements ( which the “one liner capture forces me to use ( declare in my array) anyway due to the returned field of Variant Elements ( for more than one cell ) ) and “emptying” was a good idea. Otherwise a __“”__ or a __0__ slipping in when i re paste in often chucks a type mismatch error “Spanner in the Works” at some further point. Pasting Empty Variant Elements of an Array into a sheet where i do not want anything done ( and the format not being effected ) seems fairly well behaved. Pasting in a __0 __or __“” __or__ “wot not here nothing WTF” __ as i mentioned can put a "Spanner in the works"..

Alan

---o00o---`(_)`---o00o---

 

[RoryA]

Apologies - I misread what you wrote.

I would expect A to be faster than B.

 

[DocAElstein]

Hi

......
I would expect A to be faster than B.

Thanks, sounds like the simple thing to do then
Alan