ByRef or ByVal

[Hei]

Hi,

i know the difference of ByRef and ByVal, in case if use byref or byval
don't affect the result which one should prefer? (less memory use, better
performance ....issue)

thx

[Klaus H. Probst]

Re: ByRef or ByVal

They are not the same thing. What do you mean "which one should prefer"? Use
the one that you need to use.

For example:

http://groups.google.com/groups?selm=%23MbK7UfRBHA.2084%40tkmsftngp03&oe=UTF-8&output=gplain

(watch for wrapping)


--
_______________ _____
Klaus H. Probst, MVP

http://www.vbbox.com/

"Hei" <chun_hei@msn.c om> wrote in message
news:eVR$JyYrDH A.2416@TK2MSFTN GP10.phx.gbl...[color=blue]
> Hi,
>
> i know the difference of ByRef and ByVal, in case if use byref or byval
> don't affect the result which one should prefer? (less memory use, better
> performance ....issue)
>
> thx
>
>[/color]

[Armin Zingler]

Re: ByRef or ByVal

"Hei" <chun_hei@msn.c om> schrieb[color=blue]
>
> i know the difference of ByRef and ByVal, in case if use byref or
> byval don't affect the result which one should prefer? (less memory
> use, better performance ....issue)[/color]

My personal basic rule: If the procedure shouldn't change the passed value,
declare it ByVal, otherwise ByRef.

The "passed value" is the reference to an object if it is a reference type.
The "passed value" is the object itself if it is a value type.


--
Armin

http://www.plig.net/nnq/nquote.html

http://www.netmeister.org/news/learn2quote.html

[Herfried K. Wagner [MVP]]

Re: ByRef or ByVal

* "Hei" <chun_hei@msn.c om> scripsit:[color=blue]
> i know the difference of ByRef and ByVal, in case if use byref or byval
> don't affect the result which one should prefer? (less memory use, better
> performance ....issue)[/color]

There _is_ a difference between 'ByVal' and 'ByRef'. In VB.NET, 'ByVal'
is used by default because it often makes more sense. 'ByRef' is only
relevant for reference types, if the _reference_ itself should be
changed by the procedure.

--
Herfried K. Wagner [MVP]
<http://www.mvps.org/dotnet>

[Armin Zingler]

Re: ByRef or ByVal

"Herfried K. Wagner [MVP]" <hirf-spam-me-here@gmx.at> schrieb[color=blue]
> * "Hei" <chun_hei@msn.c om> scripsit:[color=green]
> > i know the difference of ByRef and ByVal, in case if use byref or
> > byval don't affect the result which one should prefer? (less memory
> > use, better performance ....issue)[/color]
>
> There _is_ a difference between 'ByVal' and 'ByRef'. In VB.NET,
> 'ByVal' is used by default because it often makes more sense.
> 'ByRef' is only relevant for reference types, if the _reference_
> itself should be changed by the procedure.[/color]


Why do you think that ByRef is only relevant for reference types??


--
Armin

[Herfried K. Wagner [MVP]]

Re: ByRef or ByVal

* "Armin Zingler" <az.nospam@free net.de> scripsit:[color=blue][color=green][color=darkred]
>>> i know the difference of ByRef and ByVal, in case if use byref or
>>> byval don't affect the result which one should prefer? (less memory
>>> use, better performance ....issue)[/color]
>>
>> There _is_ a difference between 'ByVal' and 'ByRef'. In VB.NET,
>> 'ByVal' is used by default because it often makes more sense.
>> 'ByRef' is only relevant for reference types, if the _reference_
>> itself should be changed by the procedure.[/color]
>
> Why do you think that ByRef is only relevant for reference types??[/color]

Maybe my bad skills in the English language caused the misinterpretati on
on your side. If wanted to point out when 'ByRef' makes sense when used
with reference types.

--
Herfried K. Wagner [MVP]
<http://www.mvps.org/dotnet>

[Armin Zingler]

Re: ByRef or ByVal

"Herfried K. Wagner [MVP]" <hirf-spam-me-here@gmx.at> schrieb[color=blue]
> * "Armin Zingler" <az.nospam@free net.de> scripsit:[color=green][color=darkred]
> >>> i know the difference of ByRef and ByVal, in case if use byref
> >>> or byval don't affect the result which one should prefer? (less
> >>> memory use, better performance ....issue)
> >>
> >> There _is_ a difference between 'ByVal' and 'ByRef'. In
> >> VB.NET, 'ByVal' is used by default because it often makes more
> >> sense. 'ByRef' is only relevant for reference types, if the
> >> _reference_ itself should be changed by the procedure.[/color]
> >
> > Why do you think that ByRef is only relevant for reference
> > types??[/color]
>
> Maybe my bad skills in the English language[/color]

haha.. ;)
[color=blue]
> caused the
> misinterpretati on on your side. If wanted to point out when 'ByRef'
> makes sense when used with reference types.[/color]

I still don't understand - but, no need for an explanation. We know what
byval/byref do. ;-)


--
Armin

http://www.plig.net/nnq/nquote.html

http://www.netmeister.org/news/learn2quote.html

[Jay B. Harlow [MVP - Outlook]]

Re: ByRef or ByVal

Hei,[color=blue]
> i know the difference of ByRef and ByVal, in case if use byref or byval
> don't affect the result which one should prefer? (less memory use, better
> performance ....issue)[/color]
Are you sure you know the difference? ;-)

ByVal & ByRef Parameters are independent of Reference & Value Types. All
parameters by default are passed ByVal, you should only pass a parameter
ByRef when you have to, which is when you need to modify the callers
variable.

Less memory use & better performance should not be a factor in choosing
ByVal & ByRef. The only time to consider ByRef for less memory & performance
is when passing large structures (structures as in defined with the
Structure keyword), however structures should never be large!

Structure Usage Guidelines.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/cpconvaluetypeusageguidelines.asp

A Reference Type is an object that exists on the heap. If I have a variable
that is a reference type and assign the variable to another variable. Both
variables will be pointing to the same object on the heap.

Dim x As Person
x = New Person()
Dim y As Person
y = x

Both x & y are the exact same Person object on the heap.

A Value Type does not live on the Heap. If I have a value type variable and
I assign it to another variable, a copy of the value is made.

Dim x As Integer
x = 100
Dim y As Integer
y = x

Although both x & y have the value 100, they are physically different values
as a copy was made.

Now when you pass a variable to a ByVal parameter a copy of the variable is
made. So for a Reference Type a copy of the reference is made, which means
there is still only one object on the heap & two references to that object.
For a Value Type a copy of the value is made.

When you pass a variable to a ByRef parameter a reference to that variable
is made. So for a Reference Type you have a reference to a reference to the
object, for a Value Type you have a reference to the value.

Remember ByVal & ByRef are how parameters are passed. Reference & Value
Types are how quantities are stored.

Hope this helps
Jay


"Hei" <chun_hei@msn.c om> wrote in message
news:eVR$JyYrDH A.2416@TK2MSFTN GP10.phx.gbl...[color=blue]
> Hi,
>
> i know the difference of ByRef and ByVal, in case if use byref or byval
> don't affect the result which one should prefer? (less memory use, better
> performance ....issue)
>
> thx
>
>[/color]