Visual Basic

Marking a 'byref' param as output only

10-Jul-08 12:59

Have to make your own - see RoundButton Windows Control[^].

supercat910-Jul-08 10:16

supercat9

10-Jul-08 10:16

If I have a method which writes to a byref parameter without reading it first, is there any way I can indicate that the compiler shouldn't warn about uninitialized variables being passed to it? I'd expect it's probably something simple, but I searched and couldn't find it.

Thomas Stockwell10-Jul-08 10:38

Thomas Stockwell

10-Jul-08 10:38

Depending on which VB you are using:

VS2008: Go to project properties, under the compile tab you should see a list of warning configurations. Change them to how you see fit.

Regards,
Thomas Stockwell

Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.

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supercat910-Jul-08 10:48

supercat9

10-Jul-08 10:48

I'm using vb2005. I don't want to disable the warning globally. I merely want to indicate that in certain particular instances a certain parameter should be considered 'output only'.

Thomas Stockwell10-Jul-08 11:18

Thomas Stockwell

10-Jul-08 11:18

I am not sure if the changes made in the project properties will become global defaults or not. You can always try.

jzonthemtn10-Jul-08 11:20

10-Jul-08 11:20

Try using Out instead of ByRef.

From this page[^]:

Output parameters are very similar to reference parameters. The only differences are: 

The variable specified on the invocation doesn't need to have been assigned a value 
before it is passed to the function member. If the function member completes normally,
the variable is considered to be assigned afterwards (so you can then "read" it).

Dave Doknjas10-Jul-08 13:29

Dave Doknjas

10-Jul-08 13:29

VB doesn't have an 'out' keyword like C#, but you can use an attribute:
e.g.,
Public Sub Test(<System.Runtime.InteropServices.Out()> ByRef i As Integer)

David Anton
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jzonthemtn11-Jul-08 2:51

Crystal Report: How to obtain minimum for a subtotal value ?

11-Jul-08 2:51

Oh! Thanks, I wasn't aware of that.

David Mujica10-Jul-08 8:01

David Mujica

10-Jul-08 8:01

I currently have a report which contains both detail values and subtotal values. What I am trying to do is find the minimum values for the subtotal value. It works fine if I want to find the minimum of a detail value, but when I try to do it for the subtotal value, the Formula editor returns a "This field cannot be summarized." error message.

The formula is: Minimum ({@subMaxFlavorPct})

How to add items to the beginning of an array

darthjimmy13810-Jul-08 7:25

darthjimmy138

10-Jul-08 7:25

I want to add a string to the beginning of my array and still keep the existing strings in the array.

I'm thinking it has something to do with moving the existing items down.

Can anyone help me with this?

jzonthemtn10-Jul-08 11:17

10-Jul-08 11:17

You could move all the items in the array down one by one, but performance-wise that's probably not the best way. You could reverse[^] the array, add the new item, and then reverse the array again, which, depending upon arrays are implemented in .Net, may or may not provide any better performance.

If top performance is a priority, use a linked list[^] or Data Structures : Part 1 - Singly Linked Lists[^][^].

Luc Pattyn10-Jul-08 14:01

Luc Pattyn

10-Jul-08 14:01

Hi,

an array can't do that without a performance hit, since all its data has to be moved.
That is exactly why they invented all those other fancy data structures, such as linked lists.

Now linked lists may be too expensive for your needs (depends on how often you want to prefix something
to a loaded array). If only seldom, I would suggest a linked list of arrays, i.e. each node in the
linked list contains an array. So you would start off with a single node containing the original array,
then prefix one node with the one new data item in a single-element array.

Of course, whatever you choose, if it is not an array, then you may not get some of the nice features
an array offers, such as fast indexing, automatic sorting, reversing, etc.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Voting for dummies? No thanks. Dead | X|

Guffa10-Jul-08 15:52

Guffa

10-Jul-08 15:52

You can't add anything to an array, as it can't be resized. You would have to create a new array and copy all the data from the current array.

For a collection with a dynamic size, you should use something like a List(Of String) instead. Although you can insert an item at the beginning of a list, you should consider adding it at the end of the list intead, as that doesn't mean that every item in the list has to be moved. Which end of a list is which, only depends on how you look on it. You can just as easily loop from the last item to the first, in which case the last added items comes first.

Perhaps even a Queue(Of String) would be better for what you are doing.

Despite everything, the person most likely to be fooling you next is yourself.

Chinners11-Jul-08 0:53

Chinners

11-Jul-08 0:53

Just a quick note - an array can be resized Blush | :O

)

dim Arr(10) as string
redim Arr(100) (works, clearing array first)
redim preserve arr(100) works, preserving data...

However, I agree a list would be a better choice. You can always dump it back to an array using the .ToArray function of the variable:

dim L as list(of string)
<blah code="" filly="" stringy="" list="">
dim Arr() as string=l.ToArray.

Mind you, I guess this would take quite a hefty performance hit if doing it too often.

Mark Churchill11-Jul-08 1:04

Mark Churchill

11-Jul-08 1:04

I'm pretty sure you'll find that redim creates a new array and (optionally) copies the old data in. Logically an array can't be increased if it's packed amongst other stuff in memory without moving it anyway.

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Director
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Guffa11-Jul-08 3:33

Guffa

11-Jul-08 3:33

Jasey9 wrote:
Just a quick note - an array can be resized [Red faced] )

dim Arr(10) as string
redim Arr(100) (works, clearing array first)
redim preserve arr(100) works, preserving data...

No, it can't be resized. The ReDim Preserve command creates a new array and copies the data from the original array to it.

Despite everything, the person most likely to be fooling you next is yourself.

Chinners11-Jul-08 4:29

Chinners

11-Jul-08 4:29

Yep. That is how VB resizes an array. I never said it was efficient. I was responding to the statement saying you can’t resize an array. The original statement inferred it was a manual job to copy data from one array to another.

However, from a runtime point of view, the array has been resized. It is not be the most efficient thing to do (well, it may be more efficient on small arrays, but then I am possibly overcomplicating things Smile | :)

), But the end result of a redim will be to have changed the upper bound of the array. I would never use this sort of "feature" in a loop with lots of elements in the array, but for an occasional hit, especially if the rest of the app written is geared towards arrays, then I would say it is appropriate.

I did, however suggest that a list would be more efficient... It was just the word "CANT" I didnt like to see Smile | :)

Dave Kreskowiak11-Jul-08 8:09

Dave Kreskowiak

11-Jul-08 8:09

Jasey9 wrote:
I was responding to the statement saying you can’t resize an array

You can't. Array's dimensions are immutable. Creating a new array and copying the data is NOT resizing an existing array. It's mearly creating a new one using a very expensive process. This is not an ability unique to VB since it can be done in just about any language. The only advantage VB has over some other languages is that it's built into the VB runtime and it supply syntactic sugar to relieve you the stress of coding this little function yourself.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007, 2008

Chinners11-Jul-08 8:33

Chinners

11-Jul-08 8:33

"The only advantage VB has over some other languages is that it's built into the VB runtime"

Not sure how to quote, but the above says what I mean.

You know, I know, advanced programmers know that behind the scenes, a lot is going on (although, if the compiler has any sense it will be reduced to a "REP MOVSD" command in the end, which is very quick in small data situations).

"It's mearly creating a new one using a very expensive process"

The point I am trying to make is that in VB, there are commands that appear to resize an array. How this is done, to an average user, doesn't matter. I mean, if we were all looking for the "least expensive" ways of doing stuff, we would do most stuff in raw assembler. Sure, it will take more time to develop, but code costs running times would be reduced.

I am not meaning to start any arguments here, all I am saying is that the dimentions of an array can be changed. There are many more, optimal ways of achiving the same thing... but increasing an array using "redim" is cheaper, in terms of man hours, than developing a proper linked list. VB does hide all the inefficiences of the procedure, but to the end user, the array has been resized