dcsimg
Results 1 to 23 of 23

Thread: Help me understand why 'Finally' supercedes 'Exit Sub'

  1. #1

    Thread Starter
    PowerPoster BruceG's Avatar
    Join Date
    May 2000
    Location
    New Jersey (USA)
    Posts
    2,627

    Help me understand why 'Finally' supercedes 'Exit Sub'

    This may be obvious to those of you who have been doing .NET for a good while, but in the example below, why is it that when I say "Exit Sub" the "Finally" code still executes? (I'm thinking the "Whatever" message should never execute, but of course it does.) It seems counter-intuitive to me ...

    Code:
        Private Sub Whatever() 
    
            Try
                MsgBox("Hello")
                Exit Sub
            Catch ex As Exception
    
            Finally
                MsgBox("Whatever")
            End Try
    
        End Sub
    "It's cold gin time again ..."

    Check out my website here.

  2. #2
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    103,743

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Because the whole point of a Finally block is to ensure that its contents are executed NO MATTER WHAT. The whole idea is that once you enter a Try block the associated Finally block is guaranteed to be executed, so you can place essential cleanup code there and know for sure that it will be executed.
    Last edited by jmcilhinney; Oct 28th, 2007 at 11:55 PM.

  3. #3

    Thread Starter
    PowerPoster BruceG's Avatar
    Join Date
    May 2000
    Location
    New Jersey (USA)
    Posts
    2,627

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    OK, understood. That's something I'll have to watch out for (no early exits within a Try block that has a Finally part).
    "It's cold gin time again ..."

    Check out my website here.

  4. #4
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    103,743

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Sometimes that's exactly what you want though. If it's not then you are misusing your Finally blocks because they should only ever contain code that you absolutely want executed. That said, you should avoid using Exit Sub anyway.

  5. #5
    type Woss is new Grumpy; wossname's Avatar
    Join Date
    Aug 2002
    Location
    #!/bin/bash
    Posts
    5,683

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Finally blocks are an excuse to let your code quality drop to unaceptable levels.

  6. #6
    Frenzied Member Motoxpro's Avatar
    Join Date
    Sep 2001
    Location
    Spiro, OK
    Posts
    1,211

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by wossname
    Finally blocks are an excuse to let your code quality drop to unaceptable levels.
    That said, you should avoid using Exit Sub anyway.
    Can you guys explain why you say that?

  7. #7
    Frenzied Member
    Join Date
    May 2006
    Location
    Toronto, ON
    Posts
    1,093

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by wossname
    Finally blocks are an excuse to let your code quality drop to unaceptable levels.
    This is a nonsensical statement.

    Finally blocks are great for cleaning up resources - closing streams and connections, etc. If you're putting processing in there, then you're doing something wrong, but ignoring finally blocks means that you're letting your code quality drop to unacceptable levels.

  8. #8
    Addicted Member
    Join Date
    May 2006
    Location
    Manchester, England
    Posts
    255

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote:
    That said, you should avoid using Exit Sub anyway.

    Can you guys explain why you say that?
    Yeah - I'd like some guidance on that, too.
    At home - VB.NET 2005/2008 Express, Visual Web Developer 2005 Express
    At work - VS 2008 Standard (VB)
    .NET 2.0/3.5


    Visual Studio Express Learning Centre | How do I videos | MSDN VB Express Forum | MSDN VB Developer Centre

  9. #9
    Hyperactive Member
    Join Date
    May 2005
    Posts
    334

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    One thing I don't understand is the difference between using a Finally block & simply putting more code after the End Try. (Other than the idea that an Exit Sub inside the Try block should bypass that additional code.)

    Hopefully that additional code would be in a second Try/Catch block-is there a penalty for using multiple Try/Catch blocks in the same Sub? Otherwise it seems to me that all you need do is ensure that both the Try & all the Catch blocks 'fall thru' to the following code for it to function as a Finally block.

  10. #10
    PowerPoster techgnome's Avatar
    Join Date
    May 2002
    Posts
    32,642

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by Tom Sawyer
    This is a nonsensical statement.

    Finally blocks are great for cleaning up resources - closing streams and connections, etc. If you're putting processing in there, then you're doing something wrong, but ignoring finally blocks means that you're letting your code quality drop to unacceptable levels.
    You're right, it is a nonsensical statement... even more so when you yourself then use that statement without further explanation.

    Quote Originally Posted by penguin5000
    Quote Originally Posted by jmcilhinney
    That said, you should avoid using Exit Sub anyway.
    Yeah - I'd like some guidance on that, too.
    It's premature functional ejection.... idealy, if something goes wrong, in a sound structure, you should be able to 1) recover and continue, 2) handle it and skip anything that may go wrong after that point. That said: Sometimes in real life the rules need to be broken.

    Quote Originally Posted by calvin-c
    One thing I don't understand is the difference between using a Finally block & simply putting more code after the End Try. (Other than the idea that an Exit Sub inside the Try block should bypass that additional code.)

    Hopefully that additional code would be in a second Try/Catch block-is there a penalty for using multiple Try/Catch blocks in the same Sub? Otherwise it seems to me that all you need do is ensure that both the Try & all the Catch blocks 'fall thru' to the following code for it to function as a Finally block.
    I had trouble with this too....The point is that the code in the Finally will run NO MATTER WHAT. Even if the try fails... Finally runs. If the Try succeeds, Finally will run. It's guaranteed. What ISN'T guaranteed to run is the code that follows... especially if there is an exception. Let's say I have some database stuff in my try. If the connection fails, it drops down into my Catch, there I can log the error, then throw an error to the caller. Then in the Finally I can clean up the connection, close everything down and dispose of all my objects safely. IF I don't have the finally, as soon as I throw the exception, the sub would terminate, leaving my objects open (until the GC comes along, but there's no guarantee WHEN it will.)

    -tg
    * I don't respond to private (PM) requests for help. It's not conducive to the general learning of others.*
    * I also don't respond to friend requests. Save a few bits and don't bother. I'll just end up rejecting anyways.*
    * How to get EFFECTIVE help: The Hitchhiker's Guide to Getting Help at VBF - Removing eels from your hovercraft *
    * How to Use Parameters * Create Disconnected ADO Recordset Clones * Set your VB6 ActiveX Compatibility * Get rid of those pesky VB Line Numbers * I swear I saved my data, where'd it run off to??? *

  11. #11
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    103,743

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Excellent post tg. Says it all really.

  12. #12
    Addicted Member
    Join Date
    May 2006
    Location
    Manchester, England
    Posts
    255

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Originally Posted by penguin5000
    Quote:
    Originally Posted by jmcilhinney
    That said, you should avoid using Exit Sub anyway.

    Yeah - I'd like some guidance on that, too.

    It's premature functional ejection.... idealy, if something goes wrong, in a sound structure, you should be able to 1) recover and continue, 2) handle it and skip anything that may go wrong after that point. That said: Sometimes in real life the rules need to be broken.
    OK - I understand that for when you're using Try ... Catch ... Finally - I'd always use a finally to tidy up the problem. My 'problem' is the statement - "avoid using Exit Sub".

    I obviously WANT to program properly, and tend to use Exit commands when I simply don't need to continue with that sub/function anymore. Is that a correct way of using an Exit command - or SHOULD they be avoided in general?
    At home - VB.NET 2005/2008 Express, Visual Web Developer 2005 Express
    At work - VS 2008 Standard (VB)
    .NET 2.0/3.5


    Visual Studio Express Learning Centre | How do I videos | MSDN VB Express Forum | MSDN VB Developer Centre

  13. #13
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Location
    Sydney, Australia
    Posts
    103,743

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by penguin5000
    Is that a correct way of using an Exit command - or SHOULD they be avoided in general?
    They do serve a purpose but they should be avoided in general. It is considered by many to be proper style to have only one point of exit from a method. In that case all code paths should lead to that point. Having multiple Exit statements makes for code that is harder to read and harder to maintain. There are some situations where it can simplify code, in which case it's a good idea to use it, but in most cases well-structured code won't need an Exit statement.

  14. #14
    MS SQL Powerposter szlamany's Avatar
    Join Date
    Mar 2004
    Location
    CT
    Posts
    17,864

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Although using an EXIT SUB is, as already said, sometimes easier and used for that reason...

    We prefer to set BOOLEAN variables as a sub runs that indicate what should happen as it continues. Then you wrap logic further down the path in those IF/blocks.

    This structure makes for easier to read code. And more important, at least for us, easier to maintain and enhance.

    Code:
            Dim booFoundAPC As Boolean = False
            Try
                drc.Connection = Dcn
                drc.CommandType = Data.CommandType.Text
                drc.CommandText = "Select ConfData From APC Where ConfItem='Created'"
                strAPC = drc.ExecuteScalar.ToString
                booFoundAPC = True
                If strAPC Is Nothing Then booFoundAPC = False
            Catch ex As Exception
                booFoundAPC = False
            End Try
            If booFoundAPC Then
                drc.CommandText = "Select ConfData From APC Where ConfItem='LOCK'"
                strLock = drc.ExecuteScalar.ToString
    .
    .
    .
    booFoundAPC determines if we are going to continue to process through this sub for example. All the places it would be set to FALSE would be places that EXIT SUB could be used if you wanted to code in that fashion.

    And in any place in the code that follow we could continue the concept of setting booFoundAPC to false so that subsequent If/blocks in the sub did or did not run. Or set other more descriptive booleans to true/false...
    Last edited by szlamany; Oct 30th, 2007 at 06:21 AM.

    *** Read the sticky in the DB forum about how to get your question answered quickly!! ***

    Please remember to rate posts! Rate any post you find helpful - even in old threads! Use the link to the left - "Rate this Post".

    Some Informative Links:
    [ SQL Rules to Live By ] [ Reserved SQL keywords ] [ When to use INDEX HINTS! ] [ Passing Multi-item Parameters to STORED PROCEDURES ]
    [ Solution to non-domain Windows Authentication ] [ Crazy things we do to shrink log files ] [ SQL 2005 Features ] [ Loading Pictures from DB ]

    MS MVP 2006, 2007, 2008

  15. #15
    type Woss is new Grumpy; wossname's Avatar
    Join Date
    Aug 2002
    Location
    #!/bin/bash
    Posts
    5,683

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Since when do we have justify our blanket generalisations?

    Quote Originally Posted by Tom Sawyer
    This is a nonsensical statement.

    Finally blocks are great for cleaning up resources
    I only mean that if you rely on something as arbitrary as a finally block you'll eventually end up disguising serious flaws in the way you do things.

    Make your algorithm correct rather than dumping responsibility on the compiler.
    I don't live here any more.

  16. #16
    PowerPoster techgnome's Avatar
    Join Date
    May 2002
    Posts
    32,642

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    But wouldn't the Finally BE a part of that algorithm? It's not up to the compiler if it's going to add the finally block or not.... it's up to the developer... and it's not arbitrary. It has a clearly defined role... and it's optional too. You don't HAVE to use it... just that some times it MAY be desirable to do so.

    If one is tossing it in just to use it and for no reason at all... THEN it becomes arbitrary.


    -tg
    * I don't respond to private (PM) requests for help. It's not conducive to the general learning of others.*
    * I also don't respond to friend requests. Save a few bits and don't bother. I'll just end up rejecting anyways.*
    * How to get EFFECTIVE help: The Hitchhiker's Guide to Getting Help at VBF - Removing eels from your hovercraft *
    * How to Use Parameters * Create Disconnected ADO Recordset Clones * Set your VB6 ActiveX Compatibility * Get rid of those pesky VB Line Numbers * I swear I saved my data, where'd it run off to??? *

  17. #17
    Moderator.NET kleinma's Avatar
    Join Date
    Nov 2001
    Location
    NJ - USA (Near NYC)
    Posts
    23,383

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by wossname
    Since when do we have justify our blanket generalisations?



    I only mean that if you rely on something as arbitrary as a finally block you'll eventually end up disguising serious flaws in the way you do things.

    Make your algorithm correct rather than dumping responsibility on the compiler.
    woss, I don't know why you hate the finally block so badly... did it steal your lunch money or something?

    Here is what I would consider a valid use of the finally block in a routine (even if its overkill to have the set to nothing statements on the objects)

    Code:
            Dim CN As SqlConnection = Nothing
            Dim CMD As SqlCommand = Nothing
            Dim DR As SqlDataReader = Nothing
            Try
                CN = New SqlConnection("OPEN SESAME")
                CMD = New SqlCommand("GIVE ME RECORDS", CN)
                CN.Open()
                DR = CMD.ExecuteReader(CommandBehavior.CloseConnection)
                If DR.HasRows Then
                    While DR.Read
                        'DO SOME OF RECORDS PROCESSING HERE
                    End While
                End If
            Catch ex As Exception
                'ALERT USER OF ERROR PROCESSING DATA
            Finally
                If DR IsNot Nothing Then
                    DR.Close()
                    DR = Nothing
                End If
                If CMD IsNot Nothing Then
                    CMD.Dispose()
                    CMD = Nothing
                End If
                If CN IsNot Nothing Then
                    CN.Dispose()
                    CN = Nothing
                End If
            End Try
    this should clean up objects in the case of any type of error here in this routine. I see nothing wrong with doing things this way, so if you feel there is an issue here please let me know.


    Also as a side note, I have become a fan of using return instead of exit sub. I also don't think its bad practice to exit a subroutine if needed. It all depends on the reason why.

    For example, what if I had a routine that displays information about the currently selected item in a listview.

    Wouldn't you want the first line of that routine to be

    Code:
    If ListView1.SelectedItems.Count = 0 Then Return
    or
    Code:
            If ListView1.SelectedItems.Count = 0 Then
                MessageBox.Show("Please select a listview item first")
                Return
            End If
    Using VS.NET 2013/.NET 2.0 through 4.5 * Please mark you thread resolved using the Thread Tools above
    PLEASE INDICATE WHAT VERSION OF VB YOU USE!!!!!!!!!!!
    * If you found a post useful then please Rate it! * DO NOT PM ME WITH LINKS TO YOUR THREADS FOR ANSWERS PLEASE!

    Code Bank:Manipulate HTML Page content in the Web Browser Control from VB - Drag Drop from Windows into Win Form - Launch new default browser instance to open URL - Display Internet Image in Picturebox - Download Files From Web With Progress Bar - IP Textbox User Control - Installing .NET Framework with INNO Setup
    ZerosAndTheOne.com
    -=Matt=-

  18. #18
    type Woss is new Grumpy; wossname's Avatar
    Join Date
    Aug 2002
    Location
    #!/bin/bash
    Posts
    5,683

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by kleinma
    woss, I don't know why you hate the finally block so badly... did it steal your lunch money or something?
    Yes, yes it did. I don't want to talk about it.

    To be honest I can't think of a useful reason to have Finally unless you are going to throw an exception inside a catch{} block that the finally is attached to.
    I don't live here any more.

  19. #19
    Moderator.NET kleinma's Avatar
    Join Date
    Nov 2001
    Location
    NJ - USA (Near NYC)
    Posts
    23,383

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    what about if in the try you open a DB connection, then try to fire off your command, but an exception occurs?

    You are saying you should clean up the DB connection in the catch instead of the finally?
    Using VS.NET 2013/.NET 2.0 through 4.5 * Please mark you thread resolved using the Thread Tools above
    PLEASE INDICATE WHAT VERSION OF VB YOU USE!!!!!!!!!!!
    * If you found a post useful then please Rate it! * DO NOT PM ME WITH LINKS TO YOUR THREADS FOR ANSWERS PLEASE!

    Code Bank:Manipulate HTML Page content in the Web Browser Control from VB - Drag Drop from Windows into Win Form - Launch new default browser instance to open URL - Display Internet Image in Picturebox - Download Files From Web With Progress Bar - IP Textbox User Control - Installing .NET Framework with INNO Setup
    ZerosAndTheOne.com
    -=Matt=-

  20. #20
    type Woss is new Grumpy; wossname's Avatar
    Join Date
    Aug 2002
    Location
    #!/bin/bash
    Posts
    5,683

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    I'm saying you do what is most sensible for any given situation.

    Databases are a good example actually. It would be weird to open a DB connection and send a query in the same function unless the entire and comprehensive goal of that function was to open the DB, do a single simple query, then close the DB and return the result. That situation is easily handled in the catch, or in a set of a few specific catches.

    However a more common use would be to use a function to open the DB and nothing else. Then do the queries as required elsewhere then use another function to drop the connection. None of these things gain any benefit whatsoever from a finally block.

    If you like finally blocks then use them if they are convenient at the time, but don't design your software around them. Please don't ask me anything else because I'm losing the will to live.
    I don't live here any more.

  21. #21
    Super Moderator Shaggy Hiker's Avatar
    Join Date
    Aug 2002
    Location
    Idaho
    Posts
    34,462

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    If you lose your will, and you lose your will to live, that will just make it difficult for your heirs.

    Finally seems to me to be a form of limitted abstraction. In Kleinma's example, he closes datareaders in the Finally block. I do that a fair amount, and do it for this reason: I love datareaders and keep them around as long as I can.

    Ok, that wasn't the real reason. Actually, it would be reasonable to close the datareader in the Try block, but if an exception is thrown prior to closing the datareader, you would also have to check the state of the datareader and close it in the Catch block, which would mean that you would be duplicating the code between the two blocks. Therefore, the Finally block would be a safer route simply because the common code would be moved into a common execution location.
    My usual boring signature: Nothing

  22. #22
    Moderator.NET kleinma's Avatar
    Join Date
    Nov 2001
    Location
    NJ - USA (Near NYC)
    Posts
    23,383

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    Quote Originally Posted by Shaggy Hiker
    but if an exception is thrown prior to closing the datareader, you would also have to check the state of the datareader and close it in the Catch block, which would mean that you would be duplicating the code between the two blocks. Therefore, the Finally block would be a safer route simply because the common code would be moved into a common execution location.
    exactly why I did it. Code consolidation...
    Using VS.NET 2013/.NET 2.0 through 4.5 * Please mark you thread resolved using the Thread Tools above
    PLEASE INDICATE WHAT VERSION OF VB YOU USE!!!!!!!!!!!
    * If you found a post useful then please Rate it! * DO NOT PM ME WITH LINKS TO YOUR THREADS FOR ANSWERS PLEASE!

    Code Bank:Manipulate HTML Page content in the Web Browser Control from VB - Drag Drop from Windows into Win Form - Launch new default browser instance to open URL - Display Internet Image in Picturebox - Download Files From Web With Progress Bar - IP Textbox User Control - Installing .NET Framework with INNO Setup
    ZerosAndTheOne.com
    -=Matt=-

  23. #23
    Junior Member pRoFiT's Avatar
    Join Date
    Mar 2007
    Posts
    25

    Re: Help me understand why 'Finally' supercedes 'Exit Sub'

    okay i was looking for exit codes for vb.........i can see that finally is better then putting the close code in the catch. and after catch.
    lets psuedo this out.

    try
    open file
    read file <-- error reading
    catch
    msg ("error")
    finally
    close file

    If you dont have finally then you would have to put a close file after catch and in the catch in case of an error. finally makes it simpler by always closing the file no matter what.

    thats my 2 cents. (a month later, but...oh well)

    edit: i guess thats the same thing shaggy said its been along day.
    mov ax,13h
    int 10h

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  



Featured


Click Here to Expand Forum to Full Width