Very general Question: Writeback a Parameter

[Frankiz]

Hi everybody,

a long time I'm fed up with writing:

intThisIncreasingVariable = intThisIncreasingVariable + 1

And so I decided to write the same Sub known from Turbo Pascal: "Inc"

The hole stuff should look like this. I think you then will know what I mean:

Private Sub Form_load()
  Dim TestVar as integer
  TestVar = 1
  inc(TestVar)
  MsgBox "Should be 2 but is only: " & TextVar
End Sub

Public Sub inc(ByRef x, Optional step = 1)
  x = x + step
End Sub

But in Basic it seems to be impossible to write back to the Variable in the calling statement. Is this right?

Regards,
Frank

[KENNNY]

yeah, u cant write back to the var passed directly, i think (correct if wrong)
just put it in a function and call it like:

VarUWantIncreasing = Inc(VarUWantIncreasing)

Function:

[CODE]Public Function Inc(X as long, Optional Step = 1)

x = x + step
Inc = X

Enc Function[\CODE]

in fact i'djust carry on writing x = x + 1



------------------
cintel rules
www.cintelsoftware.co.uk

[JorgeLedo]

Just a small corection:

Public Function Inc(X as long, Optional Step = 1) as integer


So, as far as I know, you have to declare the type of the variable you want to return, even if it is a variant.

If oyu want to return deiferent type return it as a variant and then convert it to what you want (long, double, date, etc).


------------------
Jorge Ledo
[email protected]
Portugal

[Crazy D]

Change
inc(TestVar)
to
Call inc(TestVar)
and it works.

[Frankiz]

Wow!
Not bad Crazy....

Thanks

Can you explain it to me? Why does it run this way?

[Frankiz]

All right!
I got it:
Here this is also very got or even better :-)

inc myVar

or

inc myVar, 5

I remember:
If you use brackets the parameter is passed by value and if not then it is passed by reference.

All right. Thanks a lot!!

Regards,

------------------
-------------
>> Frank <<


[This message has been edited by Frankiz (edited 01-04-2000).]

[This message has been edited by Frankiz (edited 01-04-2000).]

[KENNNY]

can u give me a definition of by value and by reference?
cos i see all these ByRef and ByVal 's and its confusing

------------------
cintel rules
www.cintelsoftware.co.uk

[Frankiz]

Here is the definition from the MSDN (msdn.microsoft.com) or from CD:

by reference
------------
A way of passing the address of an argument to a procedure instead of passing the value. This allows the procedure to access the actual variable. As a result, the variable's actual value can be changed by the procedure to which it is passed. Unless otherwise specified, arguments are passed by reference.


by value
--------
A way of passing the value of an argument to a procedure instead of passing the address. This allows the procedure to access a copy of the variable. As a result, the variable's actual value can't be changed by the procedure to which it is passed.


I hope this could help. I don't know what I should add.
In our example it is necessary that the Inc-Sub works with the value stored on the adress and not with a copy of the parameter.

Regards,
Frank

[KENNNY]

cheers m8 i get it now.. its a bit like pointers in C++


------------------
cintel rules
www.cintelsoftware.co.uk

Exactly! In fact when passing by value you are creating another instance of the variable in memory and are thus consuming more resources. If you pass by reference then you are passing a pointer (address) to the function, and therefore you are addressing the location of the only variable in memory, and changing it globally, without recreating it in the local scope of the called function.

[KENNNY]

quite - so most of the time byref is better than byval.
but why do most API calls use ByVal?

------------------
cintel rules
www.cintelsoftware.co.uk