Global variable losing value for no apparent reason

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  • sgmaxmp11
    #16
    Re: Global variable losing value for no apparent reason



    "Bob Quintal" <rquintal@sPAmp atico.caà¢Õ¹໠繢éͤÇÒÁ
    news:Xns9AE961F DB3E8CBQuintal@ 66.175.223.2...


      Comment

      • lyle fairfield
        #17
        Re: Global variable losing value for no apparent reason

        Are you saying that Resume Next results in pointers to Global
        Variables being released, ie a Global String Variable length is now
        zero?

        I've never experienced that.

        Here is some code that indicates it is not so.

        Global SomeGlobal$
        ' or Public SomeGlobal

        Public Sub SomeTest()

        SomeGlobal = "SomeString "
        Debug.Print "Before Error SomeGlobal = " & SomeGlobal

        On Error Resume Next
        Err = 0
        Debug.Print 3 / 0
        If Err.Number 0 Then Debug.Print _
        Err.Description & vbNewLine & "There was an error!"
        On Error GoTo 0

        Debug.Print "After Error SomeGlobal = " & SomeGlobal

        End Sub

        'Before Error SomeGlobal = SomeString
        'Division by zero
        'There was an error!
        'After Error SomeGlobal = SomeString

        I seldom use seldom Global Variables, preferring Modularly Scoped
        Variables which are referenced by Public Functions, Registry Settings
        and CurrentProject Properties. The Public Functions can meet the
        "value lost" case by beginning with
        If len(SomeGlobal) = 0 Then InitializeSomGl obal
        where InitializeSomeG lobal is a procedure that does exactly that.

        On Jul 28, 9:44 am, Bob Quintal <rquin...@sPAmp atico.cawrote:
        Good morning Teddy,
        >
        essentially, the why of it happening is that somewhere in the code
        there is an error that is incorrectly handled, perhaps just glossed
        over with a resume next, that causes Access to clear all the global
        variables. perhaps the issue is with a query that cannot be deleted,
        or something of that nature.
        >
        The second time the routine is run, the error doesn't occur, so your
        variable is present.
        >
        Q
        >
        teddysn...@hotm ail.com wrote in
        news:80d1339e-791a-44e6-8653-746bd409fca0
        @k13g2000hse.go oglegroups.co
        m:
        >
        >
        >
        >
        >
        Weird.
        >
        I have taken over responsibility for a legacy application, Access
        2k3, split FE/BE.
        >
        The client has reported a problem and I'm investigating.  I didn't
        write the application.
        >
        The AutoExec macro calls a function "InitApplicatio n" which, in
        turn, calls a function to set the value of a global string
        variable "MyStrVar" (yes, I know, globals....)
        >
        The main form has a "Quit" button, which examines the value of
        this global variable and performs an operation depending on the
        value. However, a breakpoint at this point in the code shows that
        the variable is empty (hence the problem).
        >
        After a good deal of trial and error, I have found out what is
        happening, but not why!  The following step-by-step guide shows
        what I've found (I've added either MsgBox or breakpoints to allow
        me to figure out what's going on).
        >
        1.  Autoexec for the first time - "MyStrVar" is emptly
        2.  Call function to load variable - "MyStrVar" correctly loaded
        3.  Call function to quit application -  "MyStrVar" empty -
        PROBLEM 4.  Application quits.
        >
        Repeat the above but with slight variation
        >
        1.  Autoexec for the first time - "MyStrVar" is emptly
        2.  Call function to load variable - "MyStrVar" correctly loaded
        3.  Call function to quit application -  "MyStrVar" empty -
        PROBLEM 4.  Press RESET button in code window and close form by
        flipping to design mode - "MyStrVar" still empty
        5.  Run Autoexec for the second time - "MyStrVar" is empty
        6.  Call function to load variable - "MyStrVar" correctly loaded
        7.  Call function to quit application -  "MyStrVar" now correctly
        loaded - WHY?
        >
        At no point in the program is there an assignment to "MyStrVar"
        except in the function to load the value.  The operations that I'm
        performing manually are simply to run the AutoExec macro, and
        pressing the "Quit" button on the form. So my questions are:
        >
        a) Why is it "losing" the value between setting it and calling the
        function to quit?
        >
        b) Why does this behaviour change if I press RESET and run it
        again?
        >
        In case it might help here is the relevant code:
        >
        ' Function to load the variable
        Public Sub GetAllQueries()
        >
            Dim rcd As DAO.Recordset
        >
            Set rcd = CurrentDb.OpenR ecordset("SELEC T
            tblDatabaseQuer ies.QryID
        FROM tblDatabaseQuer ies;")
            If rcd.RecordCount 0 Then
                With rcd
                    .MoveFirst
                    Do
                        MyStrVar = MyStrVar & "*" & !QryID & "*"
                        .MoveNext
                        Loop While Not (rcd.EOF)
                End With
            End If
        >
        End Sub
        >
        'Function to quit
        Private Sub CloseDatabase_C lick()
        Dim Ref As Reference
        Dim bar As CommandBar
        Dim Qry As QueryDef
        >
        For Each Ref In References
            If Ref.Name = "Word" Then References.Remo ve Ref
            Next Ref
        For Each bar In Application.Com mandBars
            bar.Enabled = True
            Next bar
        Call subfrmManageDat abaseQueries_En ter
        >
        For Each Qry In CurrentDb.Query Defs
            If InStr(MyStrVar , "*" & Qry.Name & "*") 0 Then
                CurrentDb.Query Defs.Delete (Qry.Name)
            End If
        Next Qry
        DoCmd.DeleteObj ect acTable, "tblEditedQueri es"
        DoCmd.Quit
        End Sub
        >
        --
        Bob Quintal
        >
        PA is y I've altered my email address.
        ** Posted fromhttp://www.teranews.co m**

          Comment

          • Bob Quintal
            #18
            Re: Global variable losing value for no apparent reason

            lyle fairfield <lyle.fairfield @gmail.comwrote in
            news:a47f0afd-7f81-47a0-aa2d-4f5594c0f5ea@
            34g2000hsh.goog legroups.com
            :
            Are you saying that Resume Next results in pointers to Global
            Variables being released, ie a Global String Variable length is
            now zero?

            There exists and has to my recollection always existed a bug where
            global variables are reset on some or all unhandled errors. I do
            remember having a similar problem with an error that was handled by
            a resume next, many years ago, (Access '97, maybe even Access 2).
            Perhaps that was fixed.

            How I wrote code years ago is different than how I code today.
            That comes from experience gained on using the tools and features of
            the language. I seldom use globals any more and pay more attention
            to error handlers.

            >
            I've never experienced that.
            >
            Here is some code that indicates it is not so.
            >
            Global SomeGlobal$
            ' or Public SomeGlobal
            >
            Public Sub SomeTest()
            >
            SomeGlobal = "SomeString "
            Debug.Print "Before Error SomeGlobal = " & SomeGlobal
            >
            On Error Resume Next
            Err = 0
            Debug.Print 3 / 0
            If Err.Number 0 Then Debug.Print _
            Err.Description & vbNewLine & "There was an error!"
            On Error GoTo 0
            >
            Debug.Print "After Error SomeGlobal = " & SomeGlobal
            >
            End Sub
            >
            'Before Error SomeGlobal = SomeString
            'Division by zero
            'There was an error!
            'After Error SomeGlobal = SomeString
            >
            I seldom use seldom Global Variables, preferring Modularly Scoped
            Variables which are referenced by Public Functions, Registry
            Settings and CurrentProject Properties. The Public Functions can
            meet the "value lost" case by beginning with
            If len(SomeGlobal) = 0 Then InitializeSomGl obal
            where InitializeSomeG lobal is a procedure that does exactly that.
            >
            On Jul 28, 9:44 am, Bob Quintal <rquin...@sPAmp atico.cawrote:
            >Good morning Teddy,
            >>
            >essentially, the why of it happening is that somewhere in the
            >code there is an error that is incorrectly handled, perhaps just
            >glossed over with a resume next, that causes Access to clear all
            >the global variables. perhaps the issue is with a query that
            >cannot be deleted, or something of that nature.
            >>
            >The second time the routine is run, the error doesn't occur, so
            >your variable is present.
            >>
            >Q
            >>
            >teddysn...@hot mail.com wrote in
            >news:80d1339 e-791a-44e6-8653-746bd409fca0
            >@k13g2000hse.g ooglegroups.co
            >m:
            >>
            >>
            >>
            >>
            >>
            Weird.
            >>
            I have taken over responsibility for a legacy application,
            Access 2k3, split FE/BE.
            >>
            The client has reported a problem and I'm investigating.  I
            didn't write the application.
            >>
            The AutoExec macro calls a function "InitApplicatio n" which, in
            turn, calls a function to set the value of a global string
            variable "MyStrVar" (yes, I know, globals....)
            >>
            The main form has a "Quit" button, which examines the value of
            this global variable and performs an operation depending on the
            value. However, a breakpoint at this point in the code shows
            that the variable is empty (hence the problem).
            >>
            After a good deal of trial and error, I have found out what is
            happening, but not why!  The following step-by-step guide shows
            what I've found (I've added either MsgBox or breakpoints to
            allow me to figure out what's going on).
            >>
            1.  Autoexec for the first time - "MyStrVar" is emptly
            2.  Call function to load variable - "MyStrVar" correctly
            loaded 3.  Call function to quit application -  "MyStrVar"
            empty - PROBLEM 4.  Application quits.
            >>
            Repeat the above but with slight variation
            >>
            1.  Autoexec for the first time - "MyStrVar" is emptly
            2.  Call function to load variable - "MyStrVar" correctly
            loaded 3.  Call function to quit application -  "MyStrVar"
            empty - PROBLEM 4.  Press RESET button in code window and close
            form by flipping to design mode - "MyStrVar" still empty
            5.  Run Autoexec for the second time - "MyStrVar" is empty
            6.  Call function to load variable - "MyStrVar" correctly
            loaded 7.  Call function to quit application -  "MyStrVar" now
            correctly loaded - WHY?
            >>
            At no point in the program is there an assignment to "MyStrVar"
            except in the function to load the value.  The operations that
            I'm performing manually are simply to run the AutoExec macro,
            and pressing the "Quit" button on the form. So my questions
            are:
            >>
            a) Why is it "losing" the value between setting it and calling
            the function to quit?
            >>
            b) Why does this behaviour change if I press RESET and run it
            again?
            >>
            In case it might help here is the relevant code:
            >>
            ' Function to load the variable
            Public Sub GetAllQueries()
            >>
                Dim rcd As DAO.Recordset
            >>
                Set rcd = CurrentDb.OpenR ecordset("SELEC T
                tblDatabaseQuer ies.QryID
            FROM tblDatabaseQuer ies;")
                If rcd.RecordCount 0 Then
                    With rcd
                        .MoveFirst
                        Do
                            MyStrVar = MyStrVar & "*" & !QryID &
            "*"
                            .MoveNext
                            Loop While Not (rcd.EOF)
                    End With
                End If
            >>
            End Sub
            >>
            'Function to quit
            Private Sub CloseDatabase_C lick()
            Dim Ref As Reference
            Dim bar As CommandBar
            Dim Qry As QueryDef
            >>
            For Each Ref In References
                If Ref.Name = "Word" Then References.Remo ve Ref
                Next Ref
            For Each bar In Application.Com mandBars
                bar.Enabled = True
                Next bar
            Call subfrmManageDat abaseQueries_En ter
            >>
            For Each Qry In CurrentDb.Query Defs
                If InStr(MyStrVar , "*" & Qry.Name & "*") 0 Then
                    CurrentDb.Query Defs.Delete (Qry.Name)
                End If
            Next Qry
            DoCmd.DeleteObj ect acTable, "tblEditedQueri es"
            DoCmd.Quit
            End Sub
            >>
            >--
            >Bob Quintal
            >>
            >PA is y I've altered my email address.
            >** Posted fromhttp://www.teranews.co m**
            >


            --
            Bob Quintal

            PA is y I've altered my email address.
            ** Posted from http://www.teranews.com **

              Comment

              • The Frog
                #19
                Re: Global variable losing value for no apparent reason

                I just create a class module, and instantiate it when the application
                starts. It has all the code necessary to handle the proper set up of
                global vars and I find it keeps things neat and clean. Never had a
                problem with it resetting to 'nothing'. If I want to know a value, I
                just check the associated property :-)

                Cheers

                The Frog

                  Comment

                  • Tony Toews [MVP]
                    #20
                    Re: Global variable losing value for no apparent reason

                    teddysnips@hotm ail.com wrote:
                    >I now know what the problem is, and it was a sort of error, but a
                    >silent one. The application automates Word but for various reasons,
                    >the reference to Word cannot be static and is set dynamically at start
                    >up and removed during the closing routine:
                    Good trouble shooting.

                    However I would suggest an alternative approach to the Word reference issue.

                    Late binding means you can safely remove the reference and only have an error when
                    the app executes lines of code in question. Rather than erroring out while starting
                    up the app and not allowing the users in the app at all. Or when hitting a mid, left
                    or trim function call.

                    This also is very useful when you don't know version of the external application
                    will reside on the target system. Or if your organization is in the middle of moving
                    from one version to another.

                    For more information including additional text and some detailed links see the "Late
                    Binding in Microsoft Access" page at http://www.granite.ab.ca/access/latebinding.htm

                    As far as ADO vs DAO goes they both work just fine in Access and I see absolutely no
                    reason to convert from one to another.

                    And please ignore anything Aaron Kempf states. He is rather monomaniacial.

                    Tony
                    --
                    Tony Toews, Microsoft Access MVP
                    Please respond only in the newsgroups so that others can
                    read the entire thread of messages.
                    Microsoft Access Links, Hints, Tips & Accounting Systems at
                    Tony's Main Microsoft Access Page
                    http://www.granite.ab.ca/accsmstr.htm
                    Tony's Microsoft Access Hint's, Tips and FAQ

                    Tony's Microsoft Access Blog - http://msmvps.com/blogs/access/

                      Comment

                      • rkc
                        #21
                        Re: Global variable losing value for no apparent reason

                        On Jul 31, 7:49 am, Bob Quintal <rquin...@sPAmp atico.cawrote:
                        lyle fairfield <lyle.fairfi... @gmail.comwrote in
                        news:a47f0afd-7f81-47a0-aa2d-4f5594c0f5ea@
                        34g2000hsh.goog legroups.com
                        :
                        >
                        Are you saying that Resume Next results in pointers to Global
                        Variables being released, ie a Global String Variable length is
                        now zero?
                        >
                        There exists and has to my recollection always existed a bug where
                        global variables are reset on some or all unhandled errors. I do
                        remember having a similar problem with an error that was handled by
                        a resume next, many years ago, (Access '97, maybe even Access 2).
                        Perhaps that was fixed.
                        >
                        How I wrote code years ago is different than how I code today.
                        That comes from experience gained on using the tools and features of
                        the language. I seldom use globals any more and pay more attention
                        to error handlers.
                        On Error Resume Next handles errors as long as the code it is in is in
                        scope
                        and On Error Goto 0 has not been called.

                        To extend Lyle's example with a call to another method:

                        '------
                        On Error Resume Next
                        Err = 0
                        Call CauseError
                        If Err.Number 0 Then Debug.Print _
                        Err.Description & vbNewLine & "There was an error!"
                        On Error GoTo 0

                        Debug.Print "After Error SomeGlobal = " & SomeGlobal
                        '------

                        Sub CauseError()
                        Debug.Print 3 / 0
                        End Sub

                        The error in CauseError is handled by the calling code.

                        I would be a very scary thing indeed if On Error Resume Next did not
                        handle an error and global variables were reset because of it.




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