Returning an array by reference from a function

How do you write a function which returns a reference to an array. I
can only get a function to return a copy of the array itself. I've had
a look at some other threads in this group an the return value of a
function acts like 'by Val' returning the value only (except for
objects) can you make it return a reference instead?

cheers,
Krackers

re: Returning an array by reference from a function

> How do you write a function which returns a reference to an array. I[color=blue]
> can only get a function to return a copy of the array itself. I've had
> a look at some other threads in this group an the return value of a
> function acts like 'by Val' returning the value only (except for
> objects) can you make it return a reference instead?[/color]

Do you mean you want your function to create an array out of thin air
and then give you access to it from outside of the function? You can't
do that; things declared inside of a function or sub are local to that
procedure. Besides, if you could do that, what would that mean the next
time the function was called? Anyway, you could declare an array in the
(General)(Declarations) section of a form (making it have form-wide
scope) or as Public in a BAS module (making it have project wide scope)
and then stuff values into it from within your function (and maybe ReDim
it if necessary). Other routines could then pick up the values by simply
referencing the "global" array variable directly.

Rick - MVP

re: Returning an array by reference from a function

On 16 Jun 2004 08:07:13 -0700, Krackers <krackersk@hotmail.com> wrote:
[color=blue]
> How do you write a function which returns a reference to an array. I
> can only get a function to return a copy of the array itself. I've had
> a look at some other threads in this group an the return value of a
> function acts like 'by Val' returning the value only (except for
> objects) can you make it return a reference instead?
>
> cheers,
> Krackers[/color]


There is no way to return an array ByRef in Visual Basic. You can
(almost) always design code so this isn't needed. Dimension an array with
the proper Scope. Instead of returning an array ByRef, the function
manipulates an array with a higher Scope (ei outside the function) which
is then accessible outside the function.

The only situation where you might want to fiddle with array pointers is
when the array is very large, in a Class, and you need to access it from
outside the Class. This is because you can not declare a Public array in
a Class. In this situation, you can copy the pointer of the array in the
Class to a dummy array variable outside the Class. See example:

http://www.planetsourcecode.com/vb/s...52009&lngWId=1

If the array is not in a Class, or is not very large, then efficient code
can be designed such that array pointers aren't necessary.


-korejwa

re: Returning an array by reference from a function

Rick,

The array would be held in a class, it's scope is module level. the
function is a function of the class and I want it to return a
reference to the module level array.

the code looks something like this:

'<class arrayHolder - Start>

private mArray()

public function rtnArray() as variant()
'code to do some formating to the array
rtnArray = mArray
end function

'<class arrayHolder - end>

I then want any changes outside the class 'arrayHolder' to affect the
array in arrayHolder (mArray). To make the 'mArray' public scope means
I wouldn't be able to run code before it was accessed because any
class would be able to access it directly. If returning a variable
from a function is by value only then I'll have to make the array
public or use a collection instead of an array (collections always
pass by reference since they are an object) but this would mean a fair
amount of code rewriting. If there is a way of making the return
variable of the function by reference it would save me a lot of time.

cheers,
Krackers


"Rick Rothstein" <rickNOSPAMnews@NOSPAMcomcast.net> wrote in message news:<ZumdnahtPZeu-k3dRVn-vA@comcast.com>...[color=blue][color=green]
> > How do you write a function which returns a reference to an array. I
> > can only get a function to return a copy of the array itself. I've had
> > a look at some other threads in this group an the return value of a
> > function acts like 'by Val' returning the value only (except for
> > objects) can you make it return a reference instead?[/color]
>
> Do you mean you want your function to create an array out of thin air
> and then give you access to it from outside of the function? You can't
> do that; things declared inside of a function or sub are local to that
> procedure. Besides, if you could do that, what would that mean the next
> time the function was called? Anyway, you could declare an array in the
> (General)(Declarations) section of a form (making it have form-wide
> scope) or as Public in a BAS module (making it have project wide scope)
> and then stuff values into it from within your function (and maybe ReDim
> it if necessary). Other routines could then pick up the values by simply
> referencing the "global" array variable directly.
>
> Rick - MVP[/color]

re: Returning an array by reference from a function

Rick,

The array would be held in a class, it's scope is module level. the
function is a function of the class and I want it to return a
reference to the module level array.

the code looks something like this:

'<class arrayHolder - Start>

private mArray()

public function rtnArray() as variant()
'code to do some formating to the array
rtnArray = mArray
end function

'<class arrayHolder - end>

I then want any changes outside the class 'arrayHolder' to affect the
array in arrayHolder (mArray). To make the 'mArray' public scope means
I wouldn't be able to run code before it was accessed because any
class would be able to access it directly. If returning a variable
from a function is by value only then I'll have to make the array
public or use a collection instead of an array (collections always
pass by reference since they are an object) but this would mean a fair
amount of code rewriting. If there is a way of making the return
variable of the function by reference it would save me a lot of time.

cheers,
Krackers


"Rick Rothstein" <rickNOSPAMnews@NOSPAMcomcast.net> wrote in message news:<ZumdnahtPZeu-k3dRVn-vA@comcast.com>...[color=blue][color=green]
> > How do you write a function which returns a reference to an array. I
> > can only get a function to return a copy of the array itself. I've had
> > a look at some other threads in this group an the return value of a
> > function acts like 'by Val' returning the value only (except for
> > objects) can you make it return a reference instead?[/color]
>
> Do you mean you want your function to create an array out of thin air
> and then give you access to it from outside of the function? You can't
> do that; things declared inside of a function or sub are local to that
> procedure. Besides, if you could do that, what would that mean the next
> time the function was called? Anyway, you could declare an array in the
> (General)(Declarations) section of a form (making it have form-wide
> scope) or as Public in a BAS module (making it have project wide scope)
> and then stuff values into it from within your function (and maybe ReDim
> it if necessary). Other routines could then pick up the values by simply
> referencing the "global" array variable directly.
>
> Rick - MVP[/color]

re: Returning an array by reference from a function

"Krackers" <krackersk@hotmail.com> wrote in message
news:c01e89de.0406161821.5f627773@posting.google.c om...[color=blue]
> Rick,
>
> The array would be held in a class, it's scope is module level. the
> function is a function of the class and I want it to return a
> reference to the module level array.
>
> the code looks something like this:
>
> '<class arrayHolder - Start>
>
> private mArray()
>
> public function rtnArray() as variant()
> 'code to do some formating to the array
> rtnArray = mArray
> end function
>
> '<class arrayHolder - end>
>
> I then want any changes outside the class 'arrayHolder' to affect the
> array in arrayHolder (mArray).[/color]

You might be able to get the result you need by using an indexed
property:

Public Property Get ArrayItem(ByVal Index) As Variant
ArrayItem = mArray(Index)
End Property

Public Property Let ArrayItem(ByVal Index, ByVal RHS As Variant)
mArray(Index) = RHS
End Property

Code outside of the class can then manipulate data using:
With oArrayCls
x = .ArrayItem(4)
.ArrayItem(5) = 7
End With

and so on.

re: Returning an array by reference from a function

I'm certainly no expert when it comes to VB programming, but returning a reference to an array is common in almost all programming languages. You should not have to compromise quality by using gloabl variables for arrays.

Here is a program I wrote which I believe returns a reference to an array.

Im not sure how VB works, but im assuming it makes use of both a heap and a stack like Java. If this is the case the array would exsist in the heap, and a reference to it in the stack, there is no reason we cant point to the heap object through many references.